Abstract

Background: Anaerobic bacteria are clinically relevant pathogens with highly variable susceptibility patterns, increasing resistance, and making susceptibility tests complex to perform. Aim: To determine the in vitro antimicrobial susceptibility profile of anaerobic bacteria. Method: The susceptibility of anaerobic bacteria isolated from clinical samples processed by a university laboratory between 2019 and 2021 was investigated. Results: The susceptibility of Bacteroides spp. was 81% to clindamycin, 62% to moxifloxacin, 93% to metronidazole, and 100% to ampicillin/sulbactam and imipenem. The susceptibility of Prevotella spp. was 82% to clindamycin, 94% to moxifloxacin, 89% to metronidazole, and 100% to ampicillin/sulbactam and imipenem. Cutibacterium acnes had 42% susceptibility to clindamycin, 92% to moxifloxacin and ampicillin/sulbactam, and 100% to imipenem. Gram-positive cocci showed 75% susceptibility to clindamycin and moxifloxacin, while remaining 100% susceptible to metronidazole, ampicillin/sulbactam, and imipenem. Six percent of the isolates were multidrug resistant. Discussion: There is a high rate of resistance to clindamycin and moxifloxacin, but susceptibility to β-lactams and metronidazole remains good. Conclusion: In our setting, the empirical therapy most likely to be successful against anaerobes is β-lactams combined with a β-lactamase inhibitor, followed by metronidazole. Quinolones or clindamycin should be avoided unless susceptibility has been confirmed. © 2025 Sociedad Chilena de Infectologia. All rights reserved.