Introduction: Over the last decade, a shift in the spontaneous bacterial peritonitis (SBP) microbial pattern toward an increasing incidence of gram-positive and multidrug-resistant (MDR) bacteria has been reported. Systematic surveillance of the local microbiological scenario and antibiotic resistance is crucial to SBP treatment success. The main objective of this study was to evaluate the microbiological profile and bacterial resistance of SBP pathogens in a Portuguese cohort to allow selection of the most appropriate empirical antibiotics., Methods: This is a single-center retrospective study including 63 adult cirrhotic patients with culture-positive SBP. Patients were identified using a hospital general diagnostic database and searching for all SBP events (neutrophil count in ascitic fluid ≥250/mm 3 ) from January 1, 2012, to December 31, 2017. Patients were excluded if they had culture-negative SBP, secondary peritonitis, peritoneal dialysis, a liver transplant, or immunodeficiency. The site of SBP acquisition was classified as nosocomial if it was diagnosed 48 h or longer after hospitalization or as nonnosocomial if it was diagnosed within the first 48 h. MDR bacteria were those with an acquired resistance to at least 1 agent in 3 or more antimicrobial categories. All statistical analyses were carried out using IBM SPSS Statistics software version 22 (IBM, New York, USA)., Results: The study cohort comprised 53 (84.1%) men. The mean age of the patients was 60.6 ± 11.2 years. Alcohol was the most common etiology (88.9%) and most patients had advanced liver cirrhosis (87.1%, Child C). Gram-negative bacteria were slightly more frequent than gram-positive bacteria (56.9 vs. 43.1%). Escherichia coli was the most common pathogen (33.8%). Nineteen (31.7%) bacteria were classified as MDR. Resistance to third-generation cephalosporins, quinolones, piperacillin-tazobactam, and carbapenems was found in 31.7, 35, 26.7, and 18.3% of the cases, respectively. The rates of gram-positive bacteria were similar between nosocomial and nonnosocomial episodes (45 vs. 42.2%; p = 0.835). MDR bacteria were more common in the nosocomial group (50 vs. 23.8%; p = 0.046). Resistance to third-generation cephalosporins (50 vs. 23.8%; p = 0.046), piperacillin-tazobactam (44.4 vs. 19.1%; p = 0.041), and carbapenems (33.3 vs. 11.9%; p = 0.049) occurred more frequently in nosocomial episodes. Resistance to first-line antibiotic occurred in 29.3% of the patients, being more common in the nosocomial group (44.4 vs. 22.5%; p = 0.089)., Conclusion: Although gram-negative bacteria remain the most common causative microorganisms, our results emphasize the shift in SBP microbiological etiology, as almost half of the isolated microorganisms were gram positive. The emergence of bacteria resistant to traditionally recommended empirical antibiotics underlines the importance of basing this choice on local flora and antibiotic susceptibility data, allowing a more rational and successful use of antibiotics., Competing Interests: The authors have no conflict of interests to declare., (Copyright © 2021 by Sociedade Portuguesa de Gastrenterologia Published by S. Karger AG, Basel.)