Microbiologic Studies

OVERVIEW OF MICROBIOLOGIC STUDIES

Diagnostic Testing and Microbes

Microorganisms that cause infectious disease are defined as pathogens. Organisms that are pathogenic under one set of conditions may, under other conditions, reside within or on the surface of the body without causing disease. When organisms are present but do not cause harm to the host, they are considered commensals. When organisms multiply and cause tissue damage, they are considered pathogens, with the potential for causing or increasing a pathogenic process (Chart 7.1). Some organisms that were formerly considered insignificant contaminants or commensals have taken on roles as causative agents for opportunistic diseases in patients with HIV infection or other immunodeficiency syndromes or diseases associated with a compromised health status. Consequently, virtually any organism recovered in pure culture from a body site must be considered a potential pathogen.

Basic Concepts of Infectious Disease

Infectious processes demonstrate observable physiologic responses to the invasion and multiplication of the offending microorganisms. Once an infectious disease is suspected, appropriate cultures should be done or nonculture techniques should be used, such as serologic testing for antigens and antibodies, monoclonal antibodies, and DNA probes. Proper specimen collection and appropriate blood and skin tests are necessary to detect and diagnose the presence of the microorganism.

Opportunity for infection depends on host resistance, organism volumes, and the ability of the organism to find a portal of entry and to overcome host defenses, invade tissues, and produce toxins. Organisms may become seated in susceptible persons through inhalation, ingestion, direct contact, inoculation, breaks in natural skin or mucous membrane barriers, changes in organism volumes, alterations in normal flora balances, or changes in other host defense mechanisms.

Host Factors

The development of an infectious disease is influenced by the patient’s general health, normal defense mechanisms, previous contact with the offending organism, past clinical history, and type and location of infected tissue. Mechanisms of host resistance are detailed in the following lists:

Primary host defenses
- Anatomic barriers
  - Intact skin surfaces
  - Nose hairs
  - Respiratory tract cilia
  - Coughing and flow of respiratory tract fluids and mucus
  - Swallowing and gastrointestinal (GI) tract peristalsis
- Physiologic barriers
  - High or low pH and oxygen tension (prevents proliferation of organisms)
  - Chemical inhibitors to bacterial growth (e.g., proteases)
  - Bile acids
  - Active lysozymes in saliva and tears
  - Fatty acids on skin surfaces

Secondary host defenses (physiologic barriers)

Responses of complement, lysozymes, opsonins, and secretions

Phagocytosis

CHART 7.1 Some Common Pathogens Detectable in Body Tissues and Fluids by Diagnostic Methods

Nasopharyngeal and Oropharyngeal Specimens	Sputum	Feces
β-Hemolytic streptococci Bordetella pertussis Mycoplasma spp. Moraxella catarrhalis Herpes simplex virus Pseudomonas spp. Candida albicans Corynebacterium diphtheriae Haemophilus influenzae Neisseria meningitidis Streptococcus pneumoniae Staphylococcus aureus Enterobacteriaceae Cryptococcus neoformans Respiratory syncytial virus Influenza viruses Parainfluenza viruses Adenovirus Rhinovirus Coronavirus	Blastomyces dermatitidis Bordetella pertussis Candida albicans Coccidioides immitis Influenza viruses Streptococcus pneumoniae Pseudomonas spp. Haemophilus influenzae β-Hemolytic streptococci Histoplasma capsulatum Klebsiella spp. Mycobacterium spp. Yersinia pestis Francisella tularensis Staphylococcus aureus Mycoplasma spp. Legionella spp. Chlamydophila pneumoniae Pneumocystis spp.	Campylobacter jejuni Clostridium botulinum Entamoeba histolytica Escherichia coli Salmonella spp. Shigella spp. Staphylococcus aureus Vibrio cholerae Vibrio vulnificus Vibrio parahaemolyticus Yersinia enterocolitica Clostridium difficile Rotavirus Hepatitis A, B, and C Giardia lamblia Cryptosporidium spp. Norovirus Aeromonas sp. Plesiomonas sp. Leptospira spp.
Urine
Streptococcus agalactiae Escherichia coli, other Enterobacteriaceae Enterococcus spp. Neisseria gonorrhoeae Mycobacterium tuberculosis	Pseudomonas aeruginosa Staphylococcus aureus Staphylococcus saprophyticus Salmonella and Shigella spp. Trichomonas vaginalis Candida albicans and other yeasts Staphylococcus epidermidis
Skin	Ear
Bacteroides spp. Clostridium spp. Fungi Pseudomonas spp. Staphylococcus aureus Streptococcus pyogenes Varicella zoster virus Sarcoptes scabiei Herpes simplex virus Bacillus anthracis Treponema pallidum	Aspergillus fumigatus Candida albicans and other yeast Enterobacteriaceae β-Hemolytic streptococci Streptococcus pneumoniae Pseudomonas aeruginosa Staphylococcus aureus Moraxella catarrhalis Mycoplasma pneumoniae Peptostreptococcus spp. Bacteroides fragilis Fusobacterium nucleatum Influenza virus Respiratory syncytial virus (RSV)
Cerebrospinal Fluid	Vaginal Discharge	Urethral Discharge
Bacteroides spp. Cryptococcus neoformans Haemophilus influenzae Mycobacterium tuberculosis Neisseria meningitidis Streptococcus pneumoniae Enteroviruses Listeria monocytogenes Streptococcus agalactiae (Group B) Staphylococcus spp. Escherichia coli Herpes simplex virus Mycoplasma spp.	β-Hemolytic streptococci Candida albicans Gardnerella vaginalis Listeria monocytogenes Mycoplasma spp. Human papilloma virus Neisseria gonorrhoeae Treponema pallidum Herpes simplex virus Trichomonas vaginalis	Chlamydia trachomatis Chlamydia trachomatis Coliform bacilli Herpes simplex virus Neisseria gonorrhoeae Treponema pallidum Trichomonas vaginalis Mycoplasma spp. Ureaplasma urealyticum Human papillomavirus Mobiluncus spp. and other anaerobes

Immunoglobulin A (IgA), immunoglobulin G (IgG), and immunoglobulin M (IgM) antibody formation
Cell-mediated immune responses

Factors decreasing host resistance
- Age (very young or very old)
- Presence of chronic disease (e.g., cancer, cardiovascular disease, diabetes)
- Use or history of certain therapeutic modalities, such as radiation, chemotherapy, corticosteroids, antibiotics, or immunosuppressants
- Toxins, including alcohol; drugs (including legal, illegal, prescription, and nonprescription); venom or toxic secretions from a reptile or insect; or other nonhuman bites or punctures
- Others, including excessive physical or emotional stress states, nutritional state, and presence of foreign material at the site

COLLECTION AND TRANSPORT OF SPECIMENS

General Principles

The healthcare provider is responsible for collecting specimens for diagnostic examinations. Because procedures vary, check institutional protocols for specimen retrieval, transport, and preservation, and reporting of test results.

Specimens for bacterial culture should be representative of the disease process. Also, sufficient material must be collected to ensure an accurate examination. As an example, serous drainage from a diabetic foot ulcer with possible osteomyelitis may yield inaccurate results. In this case, a bone biopsy or purulent drainage of infected tissue would be a better specimen. Likewise, if there is a lesion of the skin and subcutaneous tissue, material from the margin of the lesion rather than the central part of the lesion would be more desirable. If a purulent sputum sample cannot be obtained to aid in the diagnosis of pneumonia, blood cultures, pleural fluid examination, and bronchoalveolar lavage (BAL) specimens are also acceptable.

It is imperative that material be collected where the suspected organism is most likely to be found, with as little contamination from normal flora as possible. For this reason, certain precautions must be followed routinely:

Observe standard precautions. Clean the skin starting centrally and going out in larger circles. Repeat several times, using a clean swab or wipe each time. If 70% alcohol is used, it should be applied for 2 minutes. Tincture of iodine requires only 1 minute of cleansing.
Bypass areas of normal flora; culture only for a specific pathogen.
Collect fluids, tissues, skin scrapings, and urine in sterile containers with tight-fitting lids. Polyestertipped swabs in a collection system containing an ampule of Stuart’s transport medium ensure adequacy of the specimen for 72 hours at room temperature.
Label specimen with the patient’s name, date, and test(s) ordered and place the specimen in a biohazard bag.

Collection Procedures

Microbiologic specimens may be collected from many sources, such as blood, tissue, pus or wound exudates or drainage, urine, sputum, feces, genital discharges or secretions, cerebrospinal fluid (CSF), and eye or ear drainage. During specimen collection, these general procedures should be followed:

Label specimens properly with the following information (institutional requirements may vary):
- Patient’s name, age, gender, address, hospital identification number, and healthcare provider’s full name
- Specimen source (e.g., throat, conjunctiva)
- Date and time of collection
- Specific studies ordered
- Clinical diagnosis; suspected microorganisms
- Patient’s history
- Patient’s immune status
- Previous and current infections
- Previous or current antibiotic therapy
- Isolation status (e.g., contact, respiratory, wound)
- Other requested information pertinent to testing
Avoid contaminating the specimen; maintain aseptic or sterile technique as required:
- Special supplies may be required:
  - For anaerobes, sterile syringe aspiration of pus or other body fluid
  - Anaerobic transport containers for tissue specimens
- Sterile specimen containers
- Precautions to take during specimen collection include:
  - Observe standard precautions.
  - Take care to maintain cleanliness outside container surfaces.
  - Use appropriately fitting covers or plugs for specimen tubes and bottles.
  - Replace sterile plugs and caps that have become contaminated.
Ensure the preservation of specimens by delivering them promptly to the laboratory. Many specimens may be refrigerated (not frozen) for a few hours without any adverse effects. Note the following exceptions:
- Urine culture samples must be refrigerated unless a preservative that allows for short-term storage at room temperature is used.
- CSF specimens should be transported to the laboratory as soon as possible. If this is problematic, the culture should be incubated (meningococci do not withstand refrigeration). Both culture bottles must be maintained at room temperature prior to being placed in the analyzer.
- Blood culture bottles must be maintained at room temperature.
Transport specimens quickly to the laboratory to prevent desiccation of the specimen and death of the microorganisms.
- For anaerobic cultures, no more than 10 minutes should elapse between time of collection and culture. Anaerobic specimens should always be placed into an anaerobic transport container.
- Feces suspected of harboring Salmonella or Shigella organisms should be placed in a special transport medium, such as Cary-Blair, if culturing of the specimen will be delayed longer than 30 minutes.
Ensure that specimen quantity is adequate. With few exceptions, the quantity of the specimen should be as large as possible. When only a small quantity is available, swabs should be moistened with sterile saline just before collection, especially for nasopharyngeal cultures.
Handle specimen collection in the following way:
- Submit entire fluid specimen collected. Do not submit fluids on swabs.
- Whenever possible, specimens should be collected before antibiotic regimens are instituted; for example, complete all blood culture sampling before starting antibiotic therapy.

Transport of Specimens by Mail

Several kits containing transport media are available for use when there is a significant delay between collection and culturing. Culture swabs (containing transport medium) are available for bacterial, viral, and anaerobic collection of specimens. Some laboratories provide Cary-Blair and polyvinyl alcohol (PVA) or non-mercury-based fixative transport vials for stool collection for culture and ova and parasite examination, respectively. Depending on the request, some specimens may have to be shipped in a Styrofoam box with refrigerant packs. This is especially true for specimens to be tested for viral examination. It is prudent to consult the reference laboratory to which specimens will be sent for information on proper collection and shipment.

According to the Code of Federal Regulations (49 CFR Part 173), a viable organism or its toxin or a diagnostic specimen (volume <50 mL) must be placed in a secure, closed, watertight container that is then enclosed in a second secure, watertight container. Biohazard labels should be placed on the outside of the container.

Specimens that are to be transported within an institution should be placed in a sealed biohazard bag. Ideally, the requisition should accompany the specimen but not be sealed inside the bag.

DIAGNOSTIC TESTING PROCEDURES

Five different categories of laboratory tests are used for the diagnosis of infections: smears and stains, cultures, tissue biopsy, serologic testing, and skin testing. Cultures and skin testing are described in detail in this chapter; serologic testing is described in Chapter 8. A brief description of each of these procedures follows.

The Smear and Stain

A smear specimen for microscopic study is usually prepared by rolling a small quantity of the specimen material across a glass slide. A drop of saline in which the specimen has been emulsified can also be
used. If the slide is also to be stained, it is generally fixed by rinsing in methanol. For direct examination of unstained material, phase-contrast microscopy can be used.

Smears are most often observed after they have been stained. Stains are salts composed of a positive and a negative ion, one of which is colored. Structures present in the specimen pick up the stain and make the organism visible under the light microscope. One staining procedure, called the negative stain, colors the background but leaves the organisms themselves uncolored. The gross structure of the organisms can then be studied.

Bacterial stains are of two major types: simple and differential. A simple stain consists of a coloring agent such as gentian violet, crystal violet, carbol-fuchsin, methylene blue, or safranine O. A thin smear of sampled organisms is stained and then observed under an oil-immersion lens. A differential stain is one in which two chemically different stains are applied to the same smear. Organisms that are physiologically different pick up different stains.

The Gram stain is the most important of all bacteriologic differential stains. It divides bacteria into two physiologic groups: gram-positive and gram-negative organisms. The staining procedure consists of four major steps: (1) staining the smear with gentian or crystal violet; (2) washing off the violet stain and flooding the smear with an iodine solution; (3) washing off the iodine solution and flooding the smear with 95% alcohol or an acetone-alcohol mixture; and (4) counterstaining the smear with safranine O, a red dye. The Gram stain permits morphologic study of the sampled bacteria and divides all bacteria according to their ability or inability to pick up one or both of the stains. Gram-positive and gram-negative bacteria exhibit different properties, which helps to identify and differentiate them.

Stains other than the Gram stain are used for examining bacteriologic smears. Some, such as the acid-fast stain, can identify organisms of the genus Mycobacterium. Other stains differentiate certain structures, such as capsules, endospores, or flagella.

Cultures

Preparation of a culture involves growing microorganisms or living tissue cells on a special medium that supports the growth of a given material. Cultures may be maintained in test tubes or Petri dishes. The container holds the culture medium, which is either solid, semisolid, or liquid. Each organism has its own special requirements for growth (proper combination of nutritive ingredients, temperature, and presence or absence of oxygen). The culture is prepared in accordance with the needs of the organism. Later, it is usually incubated to enhance growth. Acid-fast bacilli (AFB) cultures, to determine whether an individual has an active Mycobacterium tuberculosis infection, can take up to 6 weeks.

Tissue Biopsy

At times, microorganisms are isolated from small quantities of body tissue that have been surgically removed. Such tissue is removed aseptically and transferred to a sterile container to be rapidly transported to the laboratory for analysis. Generally, the specimens are finely ground in a sterile homogenizer and then stained and cultured.

Serologic Testing

Infections can be diagnosed by detection of an immunologic response specific to an infecting agent in a patient’s serum. Normal humans produce both IgM (first-response antibodies) and IgG (antibodies that may persist long after an infection) to most pathogens. For most pathogens, detection of IgM antibodies or a fourfold increase in the patient’s antibody titer is considered to be diagnostic of current infection. If the infecting agent is rare or previous exposure is unlikely (e.g., rabies virus, botulin), the presence of specific IgG antibody in a single serum specimen can be diagnostic. Methods for detecting the presence of antibodies include immunodiffusion assay, complement fixation, enzyme-linked immunosorbent assay (ELISA), indirect or direct fluorescent antibody, radioimmunoassay, and Western blot immunoassay (see Chapter 8).

Skin Testing

Skin testing determines hypersensitivity to the toxic products formed in the body by pathogens. In general, three types of skin tests are performed: scratch tests, patch tests, and intradermal tests.

BLOOD, URINE, EYE, AND EAR CULTURES

• Blood Cultures

Blood cultures are collected whenever there is reason to suspect bacteremia or septicemia. Although mild transitory bacteremia is a frequent finding in many infections, a persistent, continuous, or recurrent bacteremia indicates a more serious condition that may require immediate treatment. The expeditious detection and identification of pathogens (bacteria, fungi, viruses, and parasites) in the blood may aid in making a clinical and etiologic diagnosis.

Indications for Blood Culture

Bacteremia
Septicemia
Shock
Unexplained postoperative shock
Postoperative shock after genitourinary tract manipulation or surgery
Unexplained fever of several days’ duration
Chills and fever in patients with:
- Infected burns
- Urinary tract infection
- Rapidly progressing tissue infection
- Postoperative wound sepsis
- Indwelling venous or arterial catheter
Debilitated patients receiving:
- Antibiotics
- Corticosteroids
- Immunosuppressives
- Antimetabolites
- Parenteral hyperalimentation
Following body piercing (nose, tongue, nipples, umbilicus) with signs of infection and bacteremia

NOTE

1. During an acute febrile illness, immediately draw two separate blood samples from separate sites. Obtain cultures prior to starting antimicrobial therapy because antimicrobial therapy may interfere with bacterial growth.

2. For fever of unknown origin, two blood cultures can be initially drawn 45 to 60 minutes apart. If necessary, two more sets of samples can be drawn 24 to 48 hours later.

3. In cases of acute endocarditis, draw blood cultures as stated earlier. If results are negative, two more sets of samples may be obtained on subsequent days.

4. Parasites in the blood (Plasmodium, Trypanosoma, and Babesia) are usually detected by direct microscopic observation.

5. For infants and small children, only 1 to 5 mL of blood can safely be drawn for culture. Quantities <1 mL may be insufficient to detect bacterial organisms. In adults, cultures should optimally be 20 to 30 mL of blood.

Reference Values

Normal

Negative for pathogens

Procedure for Blood Culture

During venipuncture, because of the high potential for infecting the patient, aseptic technique must be used. Key points are listed as follows:

Observe standard precautions. The proposed puncture site should be scrubbed with an antiseptic agent such as chlorhexidine. Allow to dry for 1 to 2 minutes.
Cleanse the rubber stoppers of culture bottles with chlorhexidine and allow to air-dry.
Perform venipuncture with a sterile syringe and needle; avoid contamination of the cleansed puncture site.
Withdraw about 10 to 30 mL of blood into a 20-mL syringe or directly into the culture tubes. Because of the danger of accidental needle sticks, the practice of changing needles to transfer the specimen into blood culture bottles has been replaced by direct injection with the original phlebotomy needle.
If two culture bottles are to be inoculated (one anaerobic and one aerobic), first inoculate the aerobic bottle with the optimal, manufacturer-recommended volume and then inoculate the anaerobic bottle with the remaining, being careful not to over-inoculate. Be certain to inoculate each bottle with the optimum blood volume.
Mix both bottles gently.
Label specimens with the patient’s name, date, and tests ordered and immediately transfer them to the laboratory.
Cleanse the site with alcohol after the venipuncture because some patients are sensitive to iodine.

PROCEDURAL ALERT

Handle all blood specimens according to standard precautions.
After disinfection, do not palpate the venipuncture site unless sterile gloves are worn. Palpation is the greatest potential cause of blood culture contamination.
Specimens can be drawn from two or three different sites to exclude a skin-contaminating organism.
Collection of more than three blood cultures in a 24-hr period does not improve the detection of bacteria.
It is recommended to draw blood below an intravenous line (if possible) to prevent dilution of the sample.

Clinical Implications

Negative cultures: If all cultures, subcultures (if performed), and Gram-stained smears are negative, the blood culture may be reported as no growth after 5 to 7 days of incubation.
Positive cultures: Pathogens most commonly found in blood cultures include:
- Bacteroides spp.
- Brucella spp.
- Enterobacteriaceae
- Pseudomonas aeruginosa
- Haemophilus influenzae
- Listeria monocytogenes
- Streptococcus pneumoniae
- Enterococcus spp.
- Staphylococcus aureus, Staphylococcus epidermidis
- Streptococcus spp. including β-hemolytic streptococci
- Candida albicans
- Clostridium perfringens

Interfering Factors

Blood cultures are subject to contamination, especially by skin bacteria. These skin organisms should be identified if possible.

Interventions

Pretest Patient Care

Explain purpose of and procedure for culture. Obtain and document pertinent history of signs and symptoms of infection.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

Review test results; report and record findings. Modify the nursing care plan as needed. Monitor for bacteremia, septicemia, and other febrile illness. Counsel the patient appropriately about treatment (triple antibiotic therapy).
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

• Urine Cultures

Urine cultures are most commonly used to diagnose bacterial urinary tract infection (kidneys, ureter, bladder, and urethra). Urine is an excellent culture and growth medium for most organisms that infect the urinary tract. The combination of pyuria (pus in the urine) and significant bacteriuria strongly suggests the presence of a urinary tract infection.

General Collection Procedures for Urine Culture

Early-morning specimens should be obtained whenever possible because bacterial counts are highest at that time.
A clean-voided urine specimen of at least 3 to 5 mL should be collected into a sterile container. Catheterization and aspiration of a suprapubic or indwelling catheter are alternative methods for procuring urine specimens.
Urine specimens for culture must never be retrieved from a urine collection bag that is part of an indwelling catheter drainage system.
Ideally, urine should be transported to the laboratory and examined as soon as possible. When this is not possible, the urine can be refrigerated for up to 24 hours before being cultured.
Whenever possible, specimens should be obtained before antibiotic or antimicrobial therapy begins.
Professional health personnel should instruct the patient concerning proper specimen collection technique. Failure to isolate a causative organism is frequently the result of faulty cleansing or collection techniques that can come from lack of information about the proper collection procedure.
Provide proper supplies and privacy for cleansing and urine collection. Instruct patients in proper cleansing techniques. The patient who is unable to comply with instructions should be assisted by healthcare personnel.
The urine specimen should be properly labeled. Pertinent information includes:
- Patient’s identification information
- Healthcare provider’s name
- Suspected clinical diagnosis
- Method of collection
- Date and time obtained
- Specific chemotherapeutic agents being administered

CLINICAL ALERT

Urine is an excellent culture medium. At room temperature, it promotes the growth of many organisms. Specimen collection should be as aseptic as possible. Samples should be transported to the laboratory and examined as soon as possible. The specimen must be refrigerated or placed in a preservative if there is a delay in examination.
In the case of suspected urinary tract tuberculosis (TB), three consecutive early-morning specimens should be collected. Special care should be taken when cleaning the external genitalia to reduce the risk for contamination with commensal acid-fast Mycoplasma or Mycobacterium smegmatis.

Reference Values

Normal

Negative

Procedure for Clean-Catch (Midstream) Urine Specimen

For women
- Wash and dry hands thoroughly.
- Remove the cap from the sterile container and place it so that only the outer surface touches whatever it is placed on.
- Cleanse the area around the urinary meatus from front to back with an antiseptic wipe or sponge.
- Spread the labia apart with one hand. Hold the sterile container in the other hand, using care not to contaminate the inside surface.
- Void the first 25 mL into the toilet and then catch the rest of the urine directly into the sterile container without stopping the urine stream until sufficient quantity is collected. Hold the collection cup in such a way that it avoids contact with the legs, vulva, or clothing. Keep fingers away from the rim and inner surface of the container.
- Recap the specimen container, taking care not to contaminate the inside surface of the cap.
- Wash and dry hands thoroughly.
- Observe standard precautions when handling specimens.
For men
- Wash and dry hands thoroughly.
- Remove the cap from the sterile container and place it so that only the outer surface touches whatever it is placed on.
- Retract the foreskin completely to expose the glans.
- Cleanse the area around the meatus with antiseptic wipe or sponge.
- Void the first 25 mL of urine directly into the toilet and then void a sufficient amount of urine into the sterile specimen container. Do not collect the last few drops of urine.
- Recap the specimen container, taking care not to contaminate the inside surface of the cap.
- Wash and dry hands thoroughly.
- Observe standard precautions when handling specimens.
For infants and young children
- Use a suitable plastic collection apparatus to collect urine. Because the collection bag touches skin surfaces and picks up commensal organisms, the specimen must be analyzed as soon as possible.
- Cleanse and dry the urethral area thoroughly before applying the collection bag.
- Cover collection bag with a diaper or undergarment to prevent dislodging.
- Be aware that specimens collected by catheterization may be necessary to detect a urinary tract infection because of the contamination associated with collection bags.

Clinical Implications

A bacterial count of >100,000 colony forming units (CFU)/mL indicates infection. A mixed bacterial count of <10,000 CFU/mL does not necessarily indicate infection but rather indicates possible contamination. However, growth of a single potential pathogen to >10,000 CFU/mL may be clinically significant in a symptomatic patient.
The following organisms, when present in the urine in sufficient quantity, may be considered pathogenic:
- Escherichia coli and other Enterobacteriaceae
- Enterococcus spp.
- Neisseria gonorrhoeae
- M. tuberculosis (requires special culture media)
- P. aeruginosa
- S. aureus
- Staphylococcus saprophyticus
- Streptococci (β-hemolytic, usually group B)
- C. albicans and other yeasts
Urine samples obtained by straight catheterization, suprapubic aspiration, or cystoscopy or during surgery represent bladder urine. Growth of any isolate is considered clinically significant.

Interfering Factors

Patients who are receiving forced fluids may have urine that is sufficiently dilute to reduce the bacterial count to <100,000 CFU/mL.
Bacterial contamination comes from sources such as:
- Perineal hair
- Bacteria beneath the prepuce in male patients
- Bacteria from vaginal secretions, from the vulva, or from the distal urethra in female patients
- Bacteria from the hands, skin, or clothing

Interventions

Pretest Patient Care

Explain purpose of test, procedure for urine collection, and interfering factors.
Ensure that the cleansing procedure is done correctly to remove contaminating organisms from the vulva, urethral meatus, and perineal area so that any bacteria found in the urine can be assumed to have come only from the bladder and urethra.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

Review test results; report and record findings. Modify the nursing care plan as needed. Monitor for urinary tract infection. Counsel the patient appropriately about treatment and possible further testing.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

• Eye and Ear Cultures

Bacterial conjunctivitis, caused by S. pneumoniae, S. aureus, and H. influenzae, is the most common type of infectious conjunctivitis. Inflammation of the cornea usually follows some type of trauma to the ocular surface. Postsurgical and posttraumatic endophthalmitis is often associated with Bacillus spp. and Enterobacteriaceae in addition to the aforementioned organisms.

Acute otitis media occurs in the form of a pustule and is often caused by S. aureus. Swimmer’s ear is related to maceration of the ear from swimming or hot, humid weather; it often is caused by P. aeruginosa. Otitis media often begins as a viral infection, with a bacterial infection occurring soon afterward. In children, the most common pathogens are S. pneumoniae, H. influenzae, and Moraxella catarrhalis.

Reference Values

Normal

Low counts of S. epidermidis, Lactobacillus spp., and Propionibacterium acnes may be found in eye cultures and in the flora of the external ear.

Procedure for Eye Cultures

Observe standard precautions. Purulent material from the lower conjunctival sac or inner canthus of the eye is collected on a sterile swab and placed in transport medium. Each eye should be cultured separately.
Scrapings of the cornea with a heat-sterilized platinum spatula directly onto the medium (blood or chocolate agar, brain-heart infusion medium for fungi, or thioglycolate broth) in cases of keratitis should be obtained by an ophthalmologist. For viral culture, the material is placed into viral transport broth.
Do not refrigerate specimens or transport on ice. Deliver to the laboratory as soon as possible.

RESPIRATORY TRACT CULTURES

Three types of culture may be used to diagnose respiratory tract infections: sputum, throat swabs, and nasopharyngeal swabs. At times, the purposes for which certain tests are ordered overlap.

Reference Values

The following organisms may be present in the nasopharynx of apparently healthy persons:

C. albicans
Corynebacterium spp.
Haemophilus hemolyticus, Haemophilus parainfluenzae
Staphylococci (coagulase negative)
Streptococci (α-hemolytic)
Streptococci (nonhemolytic)
Micrococci
Lactobacillus spp.
Veillonella spp.

• Sputum Cultures

Sputum is not material from the postnasal region and is not spittle or saliva. A sputum specimen comes from deep within the bronchi. Effective coughing usually enables the patient to produce a satisfactory sputum specimen.

Indications for Collection

Sputum cultures are important for diagnosis of the following conditions:

Bacterial pneumonia
Pulmonary tuberculosis (TB)
Chronic bronchitis
Bronchiectasis
Suspected pulmonary mycotic infections
Mycoplasmal pneumonia
Suspected viral pneumonia

Reference Values

Normal

Negative: normal oral flora

Procedure

Instruct patients to provide a deep-cough specimen into a sterile container. Often, an earlymorning specimen is best. Expectorated material of 1 to 3 mL is sufficient for most examinations. Remember that good sputum samples depend on thorough healthcare worker education and patient understanding during the collection process.
Label specimens with the patient’s name, date, and test(s) ordered and note the suspected infection on the accompanying requisition.
Do not refrigerate specimens; deliver to the laboratory as soon as possible.

Interventions

Pretest Patient Care

Assess for and document signs and symptoms of infection (coughing, productive sputum, blood in sputum).
Instruct the patient that this test requires tracheobronchial sputum from deep in the lungs. Instruct the patient to take two or three deep breaths and then to take another deep breath and forcefully cough with exhalation.
Ask respiratory therapy personnel to assist the patient in obtaining an “aerosol-induced” specimen if the cough is not productive. Patients breathe aerosolized droplets of a sodium chloride-glycerin solution until a strong cough reflex is initiated. The specimen often appears watery but is in fact material directly from alveolar spaces. It should be noted on the requisition as being aerosol induced.
Remember that when pleural empyema is present, thoracentesis fluid and blood culture are excellent diagnostic specimens. Bronchial washings, BAL, and bronchial brush cultures are excellent for detecting most major pathogens of the respiratory tract.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

Review test results; report and record findings. Modify the nursing care plan as needed. Monitor for respiratory tract infections. Counsel the patient about treatment.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

• Throat Cultures (Swab or Washings)

Throat cultures are important for diagnosis of the following conditions:
- Streptococcal sore throat
- Diphtheria (obtain both throat and nasopharyngeal cultures)
- Thrush (candidal infection)
- Viral infection
- Tonsillar infection
- Gonococcal pharyngitis
- Bordetella pertussis
Throat cultures can establish the focus of infection in:
- Scarlet fever
- Rheumatic fever
- Acute hemorrhagic glomerulonephritis
Throat cultures can be used to detect the carrier state of persons harboring such organisms as:
- β-Hemolytic streptococcus
- Neisseria meningitidis
- Corynebacterium diphtheriae
- S. aureus

Reference Values

Normal

Negative: normal oral flora

Procedure

For adult patients
- Place the patient’s mouth in good visual light.
- Use a sterile throat culture kit with a polyester-tipped applicator or swab and a sterile container or tube of culture medium.
- Tilt head back. Depress the patient’s tongue with a tongue blade and visualize the throat as well as possible. Rotate the swab firmly and gently over the back of the throat, around both tonsils or fossae, and on areas of inflammation, exudation, or ulceration.
  - Avoid touching the tongue or lips with the swab.
  - Because most patients gag or cough, the collector should wear a facemask for protection.
- Place the swab into the designated receptacle so that it comes in contact with the culture medium. Label specimen with the patient’s name, date, and test(s) ordered and immediately send the specimen to the laboratory.
- Refrigerate the throat culture if examination is delayed.
For pediatric patients
- Seat the patient in the adult’s lap.
- Have the adult encircle the child’s arms and chest to prevent the child from moving.
- Place one hand on the child’s forehead to stabilize the head and to prevent movement.
- Proceed with the technique used for collection of the throat and nose culture as described for adults.
For throat washings
- Have the patient gargle with 5 to 10 mL of sterile saline solution and then expectorate it into a sterile cup.
- Remember that this method provides more specimen than a throat swab and is more definitive for viral isolation.

Interventions

Pretest Patient Care

Explain purpose of and procedure for the text to patient or parents. Assess for and document signs and symptoms of infection (pain, redness, inflammation, and/or presence of exudates).
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

Review test results; report and record findings. Modify the nursing care plan as needed. Monitor for throat infection. Counsel the patient appropriately. Assess for and document any change in signs and symptoms.
For treatment of B. pertussis (whooping cough), macrolide antibiotics (e.g., erythromycin, clarithromycin, and azithromycin) are preferred in individuals older than 1 month. An alternative is trimethoprim-sulfamethoxazole (TMP-SMX) in patients older than 2 months who cannot tolerate macrolides or are infected with a macrolide-resistant strain of B. pertussis. The Tdap vaccine protects against tetanus, diphtheria, and pertussis; the vaccine is usually given in a scheduled series of doses from birth to 6 years of age and one booster dose at age 11 years.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

• Nasopharyngeal Cultures (Swab)

Nasopharyngeal swabs are the optimal specimen for detection of B. pertussis. Nasopharyngeal swabs, aspirates, and washes are better suited for recovery of respiratory syncytial virus, parainfluenza virus, and viruses causing rhinitis.

Indications for Collection

Submitted primarily for viral cultures
B. pertussis
C. diphtheriae

Reference Values

Normal

Negative: normal oral flora

Procedure

Tip the patient’s head back to collect a nasopharyngeal specimen.
Insert a flexible, calcium alginate-tipped swab carefully through the nose into the posterior nasopharynx and rotate the swab.
Pass two swabs simultaneously through one nostril and leave in nasopharynx for 15 to 30 seconds. Repeat procedure on other nostril with same two swabs. Although the calcium alginate-tipped swabs are most commonly used, aspirated nasopharyngeal specimens, obtained through a soft rubber bulb or plastic-tipped catheter, can be used.
Take specimens from both the nasopharyngeal area and the throat for C. diphtheriae confirmation.
In some cases, vacuum-assisted or bulb-collected nasopharyngeal specimens may be necessary.
Handle specimens as follows:
- Transport specimens for viral infection in appropriate transport media and refrigerate if not cultured within a few hours.
- Do not refrigerate samples unless for diphtheria or pertussis (whooping cough).

OTHER CULTURES AND SMEARS

• Wound and Abscess Cultures

Wound infections and abscesses occur as complications of surgery, trauma, or infection that interrupts a skin surface. Material from infected wounds reveals a variety of aerobic and anaerobic microorganisms. Because anaerobic microorganisms are the preponderant microflora in humans and are consistently present in the upper respiratory, GI, and genitourinary tracts, they are also likely to invade other parts of the body to cause severe, and sometimes fatal, infections. Blood cultures should always be drawn from patients with bullous lesions, burn infections, or significant myonecrosis. Infections can also occur when individuals with open wounds are exposed to Vibrio vulnificus, a bacterium present in warm coastal waters. V. vulnificus wound infections are of serious concern in hurricane-affected areas that experience coastal flooding.

Reference Values

Normal

Clinical specimens taken from wounds can harbor any of the following microorganisms. Pathogenicity depends on the quantity of organisms present. Quantitative or semiquantitative reporting of culture results may provide information on the relative importance of the various organisms present in the lesion and also the response of the infection to antibiotic therapy.

Potential pathogens:

Actinomyces spp.
Bacteroides and Fusobacterium spp.
C. perfringens and other species
E. coli
Other gram-negative enteric bacilli
Mycobacterium marinum
Nocardia spp.
Pseudomonas spp.
S. aureus
Corynebacterium jeikeium
Enterococcus spp.
Streptococci (β-hemolytic)
Candida spp.
V. vulnificus

Procedure

Procedure for wound culture
- Observe standard precautions.
- Most wounds need some form of preparation to reduce the risk for introducing extraneous organisms into the collected specimen. In the presence of moderate to heavy pus or drainage, irrigate the wound with sterile saline until all visible debris has been washed away. When culturing chronically present wounds (pressure sores), débride the wound surface of any loose necrotic, sloughed material before culturing. Cultures of the surface alone may be misleading; biopsies of deeper tissue are recommended.
- Disinfect the surface of the wound with 70% alcohol or an iodine solution.
- Apply sterile gauze pads to absorb excess saline and to expose the culture site. Always culture highly vascular areas of granulation tissue. Wearing sterile gloves, separate margins of deep wounds with thumb and forefinger to permit insertion of the swab deep into the wound cavity. Press and rotate the swab several times over the clean wound surfaces to extract tissue fluid containing the potential pathogen. Avoid touching the swab to intact skin at the wound edges. Whenever possible, submit tissue or an aspirate of the pus.
- Immediately place the swab into the appropriate transport container.
Procedure for anaerobic collection of aspirated material
- Decontaminate the culture site with surgical soap and 70% ethyl or isopropyl alcohol.
- Aspirate at least 1 mL of fluid using a sterile 3-mL syringe and a needle of appropriate gauge. Immediately transfer the aspirate to an anaerobic transport medium.
- Aspiration cultures are commonly done for closed wounds, such as soft tissue abscesses, cellulitis, or infected skin flaps. Tissue biopsies are more often performed during surgery, when infected tissue is more easily accessible.
- Never submit a swab when a tissue sample can be obtained.

Properly label the specimen for the microbiology laboratory with the following information:

Patient identification information
Healthcare provider’s name
Date and time the specimen was collected
Anatomic site or specific source of the specimen
Type of specimen (e.g., granulation tissue, abscess fluid, postsurgical wound)
Examination requested
Patient’s diagnosis
Current antibiotic therapy, if any

Clinical Implications

Clinically significant pathogens are likely to be present in the following specimens:

Pus from deep wounds or abscesses, especially if associated with a foul odor
Necrotic tissue or débrided material from suspected gas gangrene (also known as clostridial myonecrosis and myonecrosis) infection
Samples from infections bordering mucous membranes
Postoperative wound drainage
Lower extremity ulcers from diabetic patients
Decubitus ulcers from elderly or bedridden patients

Interventions

Pretest Patient Care

Explain purpose of and procedure for wound culture. Assess for and document signs and symptoms of wound infection (redness, inflammation, presence and type of drainage, and/or fever).
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

Review test results; report and record findings. Modify the nursing care plan as needed. Monitor the site of infection. Counsel the patient appropriately about treatment.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

• Skin Cultures

The most common bacteria implicated in skin infections are Staphylococcus aureus and Streptococcus pyogenes (group A). The common abnormal skin conditions include:

Pyoderma
- Staphylococcal impetigo, characterized by bullous lesions with thin, amber, varnish-like crusts
- Streptococcal impetigo, characterized by thick crusts
Erysipelas
Folliculitis
Furuncles
Carbuncles
Secondary invasion of burns, scabies, and other skin lesions
Dermatophytoses, especially athlete’s foot, scalp and body ringworm, and jock itch

Reference Values

Normal

The following organisms may be present on the skin of a healthy person. When present in low numbers, some of these organisms may be considered normal commensals; at other times, when they multiply to excess, these same organisms may become pathogens.

Clostridium spp.
Enterobacteriaceae
Corynebacterium spp.
Enterococci
Mycobacteria
Staphylococci
Streptococci
Yeasts and fungi

Procedure

To obtain scrapings from vesicular lesions or skin:

Observe standard precautions.
Clean the affected site with sterile saline, wipe gently with alcohol, and allow it to air-dry.
Aspirate a fluid sample from fresh, intact vesicles with a 25-gauge needle attached to a tuberculin syringe, and transfer the specimen to the transport medium by ejecting it from the syringe.
If fluid cannot be aspirated, open the vesicles and use a cotton-, rayon-, or Dacron-tipped applicator to swab the base of the lesion to collect infected cells. Place the swab directly into transport medium (e.g., self-contained foam pad with Stuart’s media).
To make smears for stains, use a scalpel blade to scrape the base of the lesion, taking care not to macerate the cells. Spread scraped material in a thin layer on a slide.
Label specimen with the patient’s name, date, and tests ordered and place the specimen in biohazard bag; do not refrigerate. Immediately transport the specimen to the laboratory for bacterial, fungal, or viral cultures.

• Stool and Anal Cultures and Smears

Stool cultures are commonly done to identify bacteria associated with enteric infection. Of all specimens collected, feces are likely to contain the greatest number and greatest variety of organisms. For a routine stool culture, the stool is examined to detect and to rule out Salmonella, Shigella, Campylobacter, Aeromonas, Plesiomonas, and predominating numbers of Staphylococcus organisms; cultures for yeast, Pseudomonas, Yersinia, Vibrio, and Shiga toxin-producing E. coli have to be specifically requested, depending on laboratory practice. Clostridium difficile causes antibiotic-associated colitis. It is diagnosed by detection of the toxins.

A single negative stool culture should not be considered the end point in testing. At least three stool cultures collected on separate days are recommended if the patient’s clinical picture suggests bacterial involvement despite previous negative cultures. Moreover, once a positive diagnosis has been made, the patient’s personal contacts should also be tested to prevent a potential spread of infection.

Reference Values

Normal

The following organisms may be present in the stool of apparently healthy people:

C. albicans
Enterococcus spp.
E. coli
Proteus spp.
P. aeruginosa
Streptococcus spp.
Staphylococcus spp.

Procedure

Procedure for stool specimen collection
- Observe standard precautions.
- Use a dry container or a clean, dry bedpan to collect feces. Do not contaminate stool specimen with urine, water, soap, or disinfectants.
- Remember that a freshly passed stool is best. Diarrheal stool usually gives acceptable results.
- Select portions containing pus, blood, or mucus; 1 to 2 grams is sufficient.
- Do not retrieve stool from the toilet for specimen use.
- Do not place toilet tissue or diapers with the specimen. Either may contain bismuth, which interferes with laboratory tests.
- Transfer stool specimens from the bedpan to the container with tongue blades.
- Label the sealed specimen container with the patient’s name, date, and tests ordered and immediately send it to the laboratory.
- Place the specimen in a transport medium, such as Cary-Blair medium, if a delay of longer than 2 hours for stool culture is anticipated (from time of collection until receipt in the laboratory). Specimens processed within 2 hours of collection do not require added preservatives.
Procedure for obtaining a rectal swab
- Observe standard precautions.
- Insert the swab gently into the rectum (to a depth of at least 3 cm) and rotate it to retrieve a visible amount of fecal material (Fig. 7.1).
- Place the swab into the receptacle containing transport medium, such as Cary-Blair medium.
- Label specimen with the patient’s name, date, and test(s) ordered. Send it in a biohazard bag to the laboratory as soon as possible.
- Rectal swab may not contain sufficient sample to detect enteric pathogens. Whenever possible, stool should be submitted.
Procedure for performing cellophane tape test for pinworm (Enterobius vermicularis)
- Observe standard precautions. The tape test is indicated in cases of suspected enterobiasis (pinworms).
- Apply a strip of clear cellophane tape (not micropore or adhesive-type tape) to the perineal region. Remove and spread the tape on a slide for microscopic examination.
- Remember that a paraffin-coated swab can be used in place of the cellophane tape test. If used, place the swab within a stoppered test tube.
- Be aware that it may be necessary to make four to six examinations on consecutive days before ruling out the presence of pinworms.
- Test for pinworm eggs in the morning, before the patient has defecated or bathed.

Clinical Implications

C. albicans, S. aureus, and P. aeruginosa, found in large numbers in the stool, are considered pathogenic in the setting of previous antibiotic therapy. Alterations of normal flora by antibiotics often change the environment so that normally harmless organisms become pathogens.
Cryptosporidiosis is a cause of severe, protracted diarrhea in immunosuppressed patients. Cryptosporidium organisms can be detected by ova and parasite examination.

FIGURE 7.1. Method for obtaining the rectal culture.
Helicobacter pylori has been associated with gastritis and peptic ulcer disease. H. pylori is found only on the mucus-secreting epithelial cells of the stomach. Detection of H. pylori in gastric biopsy specimens necessitates collection of the specimens in sterile containers. Smears and cultures should be examined for the presence of this organism. Initial culture incubation requires 7 days. Therefore, results of gastric biopsy specimen cultures may take 8 to 10 days to obtain. A test for H. pylori antigen in the stool provides rapid detection of H. pylori.
C. difficile: Whenever normal flora are reduced by antibiotic therapy or other host factors, the syndrome known as pseudomembranous colitis can occur. This condition is caused by C. difficile. It may be present in small numbers in the normal person, or it may occur in the hospital environment. When normal flora are reduced, C. difficile can multiply and produce its toxins.

The definitive diagnosis of C. difficile-associated diarrhea is based on clinical criteria. Endoscopic visualization of a characteristic pseudomembrane or plaque, together with a history of antibiotic therapy, is diagnostic of C. difficile. Three laboratory tests are also available. These include stool culture for C. difficile (nonspecific; requires at least 48 hours); tissue culture for detection of cytotoxin (requires 48 hours); and rapid tests that are sensitive and specific for C. difficile antigens and toxins.

Interfering Factors

Stool from patients receiving barium, bismuth, mineral oil, or antibiotics is not satisfactory a specimen for identifying protozoa.

Interventions

Pretest Patient Care

Explain purpose of test, procedure for stool collection, and interfering factors. Assess for and document history of diarrhea, including type and length of time. Instruct the patient to defecate into a clean, dry bedpan or large-mouthed container.
Do not allow patient to defecate into the toilet bowl or urinate into the bedpan or collecting container because urine has an adverse effect on protozoa.
Do not place toilet paper into the bedpan or collection container; it may contain bismuth, which can interfere with testing.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

Review test results; report and record findings. Modify the nursing care plan as needed. Monitor for intestinal infection. Counsel the patient appropriately about treatment and possible further testing. Assess for and report any change in signs and symptoms.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

• Cerebrospinal Fluid (CSF) Cultures and Smears

Bacteriologic examination of CSF is an essential step in the diagnosis of any case of suspected meningitis. Acute bacterial meningitis is an infection of the meninges. It is a rapidly progressive, fatal infection if left untreated or if treated inadequately. Death can occur within hours of
symptom onset. Prompt identification of the causative agent is necessary for appropriate antibiotic therapy and aggressive treatment. Meningitis is caused by a variety of gram-positive and gramnegative microorganisms. Bacterial meningitis also can be secondary to infections in other areas of the body.

A smear and culture should be performed on all CSF specimens obtained from persons with suspected meningitis, whether the CSF appears clear (normal) or cloudy.

In bacterial meningitis (except TB meningitis), the CSF shows the following characteristics:

Purulence (usually)
Increased numbers of leukocytes
Preponderance of polymorphonuclear cells
Decreased CSF glucose concentration in relation to serum glucose
Elevated CSF protein concentration

In meningitis caused by the tubercle bacillus, viruses, fungi, or protozoa, the CSF shows the following characteristics:

Nonpurulent (usually)
Decreased mononuclear white cell count; increased lymphocytes
Normal or decreased CSF glucose concentration
Elevated CSF protein concentration

In those persons with suspected meningitis, the CSF is generally submitted for chemical and cytologic examinations as well as culture.

Indications for Collection

Viral meningitis
Pyogenic meningitis
TB meningitis
Chronic meningitis

Reference Values

Normal

Negative: no growth
Bacteria are not normally present in CSF. However, the specimen may be contaminated by normal skin flora during the process of CSF collection.

Procedure

Collect the specimen under sterile conditions. Three or four tubes (1 mL per tube) of CSF should be collected. The third tube is used for cell count and differential; the others can be used for microbiologic and chemical studies.
Seal immediately to prevent leakage or contamination. Label the specimen with the patient’s name, date, and tests ordered and send the specimen to the laboratory without delay.
Properly label the specimen. Alert laboratory staff so that the specimen can be examined immediately.
Notify the healthcare provider as soon as results are obtained so that appropriate treatment can be started in a timely fashion.
If the CSF specimen cannot be delivered to the laboratory immediately, the container should be stored at room temperature.
No more than 4 hours should elapse before laboratory analysis takes place because of the low survival rates of the organisms causing meningitis (especially H. influenzae and N. meningitidis).

Clinical Implications

Pathogens found in CSF include:
- Cryptococcus and other fungi
- H. influenzae
- Naegleria or Acanthamoeba spp.
- Viruses (usually enteroviruses) or herpes simplex virus
- L. monocytogenes
- M. tuberculosis
- N. meningitidis
- Streptococcus pneumoniae
- Staphylococcus aureus
- Staphylococcus epidermidis
- Streptococcus (group B)
- Treponema pallidum
- Toxoplasma gondii
Positive CSF cultures occur in:
- Meningitis
- Trauma
- Abscess of brain or ependyma of spine
- Septic thrombophlebitis of venous sinuses

• Cervical, Urethral, Anal, and Oropharyngeal Cultures and Smears for Gonorrhea and Other Sexually Transmitted Infections (STIs)

These tests are done for patients with genital ulcers, vaginal lymphadenopathy, bacterial vaginosis (pathogens such as Gardnerella, Bacteroides, Prevotella, and Mobiluncus), lesions affecting epithelial surfaces, signs and symptoms of bacterial sexually transmitted infections (STIs), pelvic inflammatory disease, urethritis, or abnormal discharge and itching.

Reference Values

Normal

Negative: normal flora; negative for pathogenic antigens

Procedure

For cervical specimens
- Be aware that the cervix is the best site from which to obtain a culture specimen.
- Observe standard precautions.
- Moisten the vaginal speculum with warm water; do not use a lubricant. Remove cervical mucus, preferably with a cotton ball held in a ring forceps.
- Insert a sterile, cotton-tipped swab into the endocervical canal; move the swab from side to side; allow 30 seconds for absorption of organisms by the swab (Fig. 7.2).
FIGURE 7.2. Method for obtaining the endocervical specimen.

FIGURE 7.3. Method for obtaining the urethral specimen.
For vaginal specimens
- A vaginal fluid sample is collected on a swab by contacting the lower one third of the vaginal wall. The swab is placed for 10 minutes in a test vessel to which a developer solution has been added. The solution will turn blue or green if positive (OSOM BVBLUE Test, Sekisui Diagnostics, Lexington, MA).
- Using an immunographic assay, a vaginal fluid sample is obtained by a swab that is subsequently placed in a test tube to which a sample buffer has been added. The results are read after 10 minutes (OSOM Trichomonas Rapid Test, Sekisui Diagnostics, Lexington, MA).
For urethral specimens (male patients)
- Use a sterile swab to obtain the specimen from the anterior urethra by gently scraping the urethral mucosa (Fig. 7.3).
- Rotate the swab 360° to dislodge some of the epithelial cells for Chlamydia trachomatis. N. gonorrhoeae organisms inhabit the exudate, whereas C. trachomatis organisms are intracellular (within the epithelial cells).
For anal canal specimens
- Insert a sterile, cotton-tipped swab approximately 2.5 cm into the anal canal. (If the swab is inadvertently pushed into feces, use another swab to obtain the specimen.)
- Move the swab from side to side in the anal canal to sample the crypts; allow several seconds for absorption of organisms by the swab.
- Remember that this site is likely to be positive in a patient with STI, when a cervical specimen is negative.
Swabs for culture should be transported to the laboratory in Stuart’s transport medium and should be held at room temperature until processed.
If specimens are not processed within 12 hours, they should be refrigerated. Recovery of a pathologic organism may be more difficult because of delay in processing.

Interventions

Pretest Patient Care

Explain purpose of and procedure for specimen collection. Assess for and document signs and symptoms of infection (drainage, pain, itching).
Place the patient in the dorsal lithotomy position and appropriately drape for genital procedures. Provide as much privacy as possible.
Observe standard precautions.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient appropriately.
Explain need for possible follow-up testing and treatment. The use of pre-exposure vaccines (e.g., hepatitis A and B [frequently sexually transmitted] and human papillomavirus) is the most effective means of preventing STIs.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

• Tissue, Bone, and Body Fluid Cultures

Types of fluid collected for bacterial, viral, or fungal culture include pleural, ascitic, synovial, and pericardial fluid. Tissues may have to be minced or ground to release trapped bacteria before culturing.

Reference Values

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