Antimicrobial Susceptibility Patterns of Anaerobic Bacteria at an Irish University Hospital over the past Decade

Abstract

Background Various studies have demonstrated poor outcomes in infections caused by anaerobic bacteria due to inappropriate therapy, directly due to emergence of resistant strains. To date there is a paucity of available data on antimicrobial resistance trends of anaerobic bacteria among the Irish population, and our study aims to determine such patterns among isolates processed at our institution over the previous decade. Methodology Selected anaerobic bacteria isolated from clinical specimens processed at our laboratory from January 2010 to January 2020 inclusive were collected and studied. Bacteria were identified using MALDI-TOF, with VITEK and E-tests for antimicrobial susceptibility testing. Data was processed through WHONET. Results A total of 2098 clinically significant anaerobic bacterial isolates 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). Bacteroides spp and Prevotella spp were unsurprisingly highly penicillin-resistant at 98.8% (n=680) and 77% (n=114) respectively. Resistance rates against metronidazole were expectedly high amongst Propionibacterium spp (100%, n=341), Actinomyces spp (98.8%, n=79), Lactobacillus spp (59.7%, n=95) and Bifidobacterium spp (53.8%, n=7); whilst remaining anaerobes were largely susceptibility. All isolates were particularly susceptible to co-amoxiclav, piperacillin-tazobactam and meropenem. Clindamycin exhibited a more variable susceptibility pattern, from 6.7% resistance in Staphylococcus saccharolyticus to 81.1% resistance in Prevotella spp. Conclusion Metronidazole and beta-lactams remain highly efficacious against the majority of anaerobic isolates reviewed, and remain the backbone of empiric therapy in suspected infections. However, it remains important for periodic surveillance of resistance trends.