Antimicrobial susceptibility patterns of anaerobic bacteria at an Irish University Hospital over a ten-year period (2010–2020)

Abstract

ObjectivesIn recent years various clinical studies have demonstrated poor outcomes in infections caused by anaerobic bacteria due to inappropriate therapy, directly due to emergence of resistant strains. This is a concern given that many anaerobic infections are treated empirically with metronidazole or a beta-lactam/beta-lactamase inhibitor combinations (e.g., co-amoxiclav, piperacillin-tazobactam). To date there is a paucity of available data on antimicrobial resistance trends of anaerobic bacteria in Ireland, and our study aims to determine such patterns among isolates processed at our institution over the last ten years. MethodsSignificant anaerobic bacteria isolated from clinical specimens processed at our laboratory from January 2010 to January 2020 inclusive were reviewed. Bacteria were identified using MALDI-TOF, with E-tests used for antimicrobial susceptibility testing. Data was processed through WHONET. ResultsA total of 2098 clinically significant anaerobic bacterial isolates from blood cultures (31%), theatre/intraoperative specimens (30%), aspirates and drain fluid (22%) and wound swabs (17%) were reviewed during the study period; with the majority of isolates being Bacteroides spp (32.79%, n = 688) and Clostridium spp (18.68%, n = 392). With isolates demonstrating well-recognised or inherent resistances excluded, overall resistance to tested antimicrobials was 6.40% to penicillin, 1.71% to metronidazole, 1.43% to co-amoxiclav, 13.63% to clindamycin, 0.43% to piperacillin-tazobactam and 0% to meropenem. ConclusionMetronidazole and beta-lactam/beta-lactamase inhibitor combinations remain highly efficacious against the majority of anaerobic isolates reviewed, and can safely be used as empiric therapy in suspected anaerobic infections. However, periodic surveillance of resistance trends remains important.