An integrated centrifugation-washing-lysis method significantly improves microbiological diagnosis of spontaneous bacterial peritonitis.

Culture-negative spontaneous bacterial peritonitis (SBP) remains a major diagnostic challenge in patients with cirrhotic ascites, largely due to prior antibiotic exposure, low bacterial burden, and phagocytosis of bacteria. To address these factors and reduce false-negative results, we developed an integrated centrifugation-washing-lysis method and evaluated its impact on diagnostic turnaround time and antimicrobial stewardship. Ascitic fluid was concentrated and washed, followed by selective leukocyte lysis with 0.5% Triton X-100 (optimized to lyse host cells while preserving bacterial viability during 1-min incubation). The resulting pellet was inoculated onto solid media (chocolate and blood agar). This method was prospectively evaluated against standard bedside inoculation into aerobic and anaerobic blood culture bottles using 160 ascitic fluid samples from patients with clinically suspected SBP. The modified culture method demonstrated a significantly higher positivity rate (30.6% [49/160] vs 13.8% [22/160];