Predominant Gram-Positive Etiology May Be Associated with a Lower Mortality Rate but with Higher Antibiotic Resistance in Spontaneous Bacterial Peritonitis: A 7-Year Study in a Tertiary Center in Romania

(1) Background: Spontaneous bacterial peritonitis (SBP) is associated with a 20% mortality and is mainly caused by Gram-negative bacteria (GNB); Gram-positive bacteria (GPB) were predominant in some areas; and increased antibiotic resistance was recorded. (2) Methods: A retrospective study was performed between 2018 and 2024. The type of isolated strains, antibiotic susceptibility, and mortality (in-hospital; 30-day; 90-day; and 1-year) were estimated; multivariate analyses evaluated predictive factors for in-hospital mortality risk. (3) Results: 45 culture-positive SBP, 28 culture-negative SBP, 6 bacterascites, and 670 control ascites were diagnosed; GPB represented 60%; two Candida peritonitis and 11 polymicrobial peritonitis (21.6%) were noted (without surgery; peritoneal dialysis; or tegumentary lesion). High resistance rates to cephalosporins and quinolones, and high carbapenem resistance for nosocomial GNB were recorded. A low resistance rate to Tigecycline was noted in all infection types; GPB was susceptible to Linezolid and Vancomycin; and GNB was susceptible to Aztreonam and Colistin. In-hospital mortality was 26.7% (40% for GNB-SBP; 20% for GPB-SBP), similar to culture-negative SBP (21.3%), and higher than in the control group (9%); long-term mortality remained higher. (4) Conclusions: microbial changes to GPB etiology and increasing resistance were noted, but with a lower mortality compared to GNB; higher mortality rates up to 1 year for culture-positive and culture-negative SBP were recorded.