What is the most common organism in adult spontaneous bacterial peritonitis (SBP)?

Most Common Organism in Adult Spontaneous Bacterial Peritonitis

Escherichia coli (E. coli) is the most common organism causing spontaneous bacterial peritonitis (SBP) in adults with cirrhosis. 1

Microbiology of SBP

• SBP is typically monomicrobial and most commonly caused by gram-negative aerobic bacteria, with E. coli being the predominant pathogen (occurring in approximately 32-67% of culture-positive cases) 1, 2
• Other common causative organisms include:
  • Klebsiella species 1
  • Streptococcus species 1
  • Enterococcus species (found in approximately 15.7% of cases) 1

Changing Epidemiology of SBP

• Recent studies have shown a shift in the microbial spectrum of SBP with increasing prevalence of gram-positive organisms, particularly in healthcare settings 3, 4

• In nosocomial (hospital-acquired) SBP, there is a higher prevalence of:

  • Enterococcus species 1
  • Staphylococcus species 1, 4
  • Enterobacter species 1

• The epidemiology differs between community-acquired and nosocomial infections:

  • Community-acquired SBP: Gram-negative bacteria predominate (especially E. coli) 1
  • Nosocomial SBP: Gram-positive infections are more common 1

Antibiotic Resistance Patterns

• There is increasing resistance to quinolones among gram-negative bacteria in SBP, with approximately 30% of isolated gram-negative bacteria being resistant to quinolones 1
• In patients on norfloxacin prophylaxis, SBP is more likely to be caused by quinolone-resistant gram-negative bacteria or gram-positive cocci 1
• The rate of cephalosporin-resistant gram-negative bacteria remains relatively low in patients with SBP 1

Clinical Implications

• Third-generation cephalosporins remain the first-line empirical treatment for community-acquired SBP due to their effectiveness against E. coli and other common pathogens 1
• For patients who develop SBP while on quinolone prophylaxis, cefotaxime or amoxicillin/clavulanic acid are recommended 1
• In healthcare settings or for nosocomial SBP, broader coverage may be needed due to the higher prevalence of resistant organisms 1, 3

Common Pitfalls to Avoid

• Failing to perform diagnostic paracentesis in all cirrhotic patients with ascites admitted to the hospital, as SBP may be asymptomatic in up to one-third of cases 1
• Not considering the possibility of secondary bacterial peritonitis (due to intestinal perforation) when multiple organisms are isolated from ascitic fluid 1
• Using quinolones empirically in patients already on quinolone prophylaxis or in areas with high quinolone resistance 1
• Delaying antibiotic treatment while waiting for culture results, as prompt empiric therapy is essential for improving outcomes 1, 5