Microbiology in Pathology

BACTERIA

What are the various bacterial morphologies?

Cocci (circular), bacilli (rods), spiral (spirochetes), branching/filamentous

What other feature along with morphology is used to distinguish bacteria?

Gram stain (positive or negative)

What substance in the cell wall is unique to gram-negative bacteria?

Lipopolysaccharide (endotoxin)

What effects does lipopolysaccharide (LPS) have on the infected host?

It causes macrophage activation, complement activation, and Hageman factor activation which, via cytokine release and pathway activation, can cause fever, hypotension, edema, and possibly diffuse intravascular coagulation (DIC).

What substance in the cell wall is unique to gram-positive bacteria?

Teichoic acid

What structure of bacteria facilitates adherence to surfaces (eg, IV lines)?

Glycocalyx

What is the phase of bacterial growth that represents a “no-growth” phase due to depletion of available nutrients?

Stationary phase

What are the encapsulated bacteria?

Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae, and Klebsiella pneumoniae

What are the obligate intracellular bacteria?

Rickettsia and Chlamydia—these organisms cannot synthesize their own ATP

What are the facultative intracellular anaerobes?

Neisseria, Salmonella, Brucella, Listeria, Legionella, Yersinia, Francisella, and Mycobacterium

What are the obligate anaerobic bacteria?

Clostridium, Bacteroides, and Actinomyces

What are the spore-forming bacteria?

Clostridium tetani, Clostridium perfringens, and Bacillus anthracis

What are the most common spirochetes?

Borrelia, Leptospira, and Treponema

What gram-positive cocci is catalase and coagulase positive?

Staphylococcus aureus (occurs in clusters)

What gram-positive cocci occur in chains?

Streptococcus (catalase negative)

What are the major groupings of Streptococcus species?

Alpha-hemolytic, beta-hemolytic, and nonhemolytic

How are beta-hemolytic Streptococcus species further subdivided?

Into groups A, B, C, D, and G according to Lancefield antigens (specific carbohydrates expressed in the bacterial cell wall)

Infection with which bacteria (usually bacteremia) is associated with concurrent colon cancer?

Streptococcus bovis

What gram-negative rod can cause malignant otitis externa in diabetics, hot tub f olliculitis, and pneumonitis especially in patients with cystic fibrosis?

Pseudomonas aeruginosa

What are the gram-negative cocci (diplococci)?

Neisseria gonorrhoeae and N. meningitidis

Which bacterium has no cell wall and commonly is associated with high IgM titers?

Mycoplasma pneumoniae

What stain should be done to detect and help classify most bacteria?

Gram stain

Which bacteria generally do not Gram stain well?

Treponema, Rickettsia, Mycoplasma, Legionella, Chlamydia, and Mycobacterium

What technique is used to visualize Treponemes?

Darkfield microscopy with florescent antibody staining

What antibody serum test is most specific for syphilis?

Fluorescent Treponemal Antibody–Absorption test (FTA-Abs)

What are the common causes of false positive VDRLs?

Viral infection, drugs, rheumatic fever, SLE, and leprosy

What stain should be done to detect Mycobacterium?

Acid-fast stain helps detect “red snappers”

What stain can help detect Legionella and fungi like Pneumocystis jiroveci (formerly carinii)?

Silver stain

What stain can help detect Campylobacter and Borrelia?

Giemsa stain

What culture media is needed to isolate N. gonorrhoeae

Thayer-Martin media

What culture media is needed to isolate H. influenza

Chocolate agar

What culture media is required to isolate Legionella?

Charcoal yeast with high concentrations of iron and cysteine

What bacteria grow pink colonies on MacConkey agar?

Lactose-fermenting enteric bacteria, including Escherichia coli, Enterobacter, Serratia, and Klebsiella

What test can be used to distinguish among nonlactose fermenting bacteria?

Oxidase test—Shigella, Salmonella, and Proteus are oxidase negative, Pseudomonas is oxidase positive

Which bacteria produce superantigens?

Staphylococcus aureus (TSST-1) and Streptococcus pyogenes (Scarlet fever-erythrogenic toxin)

Which bacteria produce A-B toxins?

Corynebacterium diphtheriae, Vibrio cholerae, E. coli, and Bordetella pertussis

What is the Shiga toxin?

A toxin produced by Shigella and E. coli O157:H7 that cleaves host cell rRNA

What bacterium is associated with skin infection after animal bites?

Pasturella multocida

VIRUSES

In general, what laboratory techniques are used to detect/identify viruses?

PCR, viral culture, antibody tests

What is the genetic ploidy of viruses?

All viruses are haploid (1 copy the complete DNA or RNA genome) except retroviruses which are diploid. This should not be confused with number of strands of DNA or RNA, as some viruses are single stranded while others are double stranded.

Where do DNA viruses undergo replication in host cells?

All DNA viruses undergo replication in the nucleus except for poxviruses where it occurs in the cytoplasm.

Where do RNA viruses undergo replication in host cells?

All RNA viruses undergo replication in the cytoplasm, except influenza virus and retroviruses (both of which replicate in the nucleus).

What is a Tzanck test and what does it detect?

This is a smear of sample taken from an opened vesicle used to detect multinucleated giant cells seen in herpes infections including HSV-1, HSV-2, and VZV (varicella).

What virus causes fever, pharyngitis, lymphadenopathy, atypical T cells, and a positive heterophile antibody test?

Ebstein Barr virus (EBV), causing infectious mononucleosis

What virus classically has inclusions that look like “owl’s eyes”?

Cytomegalovirus (CMV)

What virus is associated with fever, emesis, jaundice, and Councilman bodies (acidophilic inclusions) in the liver?

Yellow fever virus (Flavivirus)

What viral infection produces paresthesias, headache, fever, central nervous system (CNS) excitability, foaming at the mouth, and paralysis?

Rabies virus

What is the name and location of the inclusion body seen in rabies virus infection?

Negri bodies—eosinophilic, cytoplasmic inclusion in neurons, most commonly in pyramidal cells of the hippocampus

What and why must a confirmatory test be done if an HIV ELISA comes back positive?

ELISA is a screening test, therefore highly sensitive but may result in false-positive test results. HIV Western blot is needed to confirm the diagnosis because it is highly specific; therefore, a positive result on Western blot will confirm the ELISA diagnosis and a negative result on Western blot will identify a false-positive ELISA test.

What neoplasms are associated with HIV infection?

Kaposi sarcoma (HHV-8), primary CNS lymphoma, non-Hodgkin lymphoma, and cervical carcinoma (HPV)

What serologic marker/s would be expected to be positive in an individual vaccinated against Hepatitis B virus?

Hepatitis B surface antibody (HBsAb) only

What serologic marker/s would be expected to be positive in an individual who cleared a previous Hepatitis B infection?

HBsAb and Hepatitis B core antibody (HBcAb)

What serologic marker/s would be expected to be positive in an individual who was a chronic carrier of Hepatitis B virus?

Hepatitis B surface antigen (HBsAg) and HBcAb

FUNGI

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