Stomach – virtually sterile; some GPCs, some yeast
Proximal small bowel – 105 bacteria, mostly GPCs
Distal small bowel – 107 bacteria, GPCs, GPRs, GNRs
Colon – 1011 bacteria, almost all anaerobes, some GNRs, GPCs
Anaerobes (anaerobic bacteria)
• Most common organisms in the GI tract
• More common than aerobic bacteria in the colon (1,000:1)
• Bacteroides fragilis – most common anaerobe in the colon
Escherichia coli – most common aerobic bacteria in the colon
FEVER
| Atelectasis |
| Urinary tract infection |
| Wound infection |
GRAM-NEGATIVE SEPSIS
E. coli most common
Endotoxin (lipopolysaccharide lipid A) is released
Endotoxin triggers the release of TNF-α (from macrophages), activates complement, and activates coagulation cascade
Early gram-negative sepsis – ↓ insulin, ↑ glucose (impaired utilization)
Late gram-negative sepsis – ↑ insulin, ↑ glucose secondary to insulin resistance
Hyperglycemia – often occurs just before the patient becomes clinically septic
Optimal glucose level in a septic patient – 100–120 mg/dL
CLOSTRIDIUM DIFFICILE COLITIS
Dx: C. difficile toxin
Tx: oral – vancomycin or Flagyl; IV – Flagyl; lactobacillus can also help
Stop other antibiotics or change them
ABSCESSES
90% of abdominal abscesses have anaerobes
80% of abdominal abscesses have both anaerobic and aerobic bacteria
Abscesses are treated by drainage
Usually occur 7–10 days after operation
Antibiotics for an abscess are needed in patients with diabetes, cellulitis, clinical signs of sepsis, fever, elevated WBC, or who have bioprosthetic hardware (eg mechanical valves, hip replacements)
WOUND INFECTION (SURGICAL SITE INFECTION)
Clean (hernia): 2%
Clean contaminated (elective colon resection with prepped bowel): 3%–5%
Contaminated (gunshot wound to colon with repair): 5%–10%
Gross contamination (abscess): 30%
Prophylactic antibiotics are given to prevent surgical site infections (stop within 24 hours of end operation time, except cardiac, which is stopped within 48 hours of end operation time)
Staphylococcus aureus – coagulase-positive
• Most common organism overall in surgical wound infections
Staphylococcus epidermidis – coagulase-negative
Exoslime released by staph species is an exopolysaccharide matrix
E. coli – most common GNR in surgical wound infections
B. fragilis – most common anaerobe in surgical wound infections
• Recovery from tissue indicates necrosis or abscess (only grows in low redox state)
• Also implies translocation from the gut
≥ 105 bacteria needed for wound infection; less bacteria is needed if foreign body present
Risk factors for wound infection: long operations, hematoma or seroma formation, advanced age, chronic disease (eg COPD, renal failure, liver failure, diabetes mellitus), malnutrition, immunosuppressive drugs
Surgical infections within 48 hours of procedure
• Injury to bowel with leak
• Invasive soft tissue infection – Clostridium perfringens and beta-hemolytic strep can present within hours postoperatively (produce exotoxins)
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