In Vitro Antibiotic Susceptibilities of Anaerobic Bacteria Isolated from Clinical Samples

Introduction: Anaerobic bacteria, which constitute a significant part of human mouth, gastrointestinal tract, genitourinary system and skin microbiota can cause serious infections of exogenous or endogenous origin. Sampling, cultivation and incubation of anaerobic infections require special conditions. Empirical antibiotic therapy is frequently preferred for anaerobic bacterial infections due to long lasting microbiological diagnosis. Periodic monitoring of regional resistance data is essential to guide empirical treatments. In this study, it was aimed to identify anaerobic microorganisms isolated from various clinical samples sent to our laboratory by matrix-assisted laser desorption/ionization time-of-flight, mass spectrometry (MALDI-TOF MS) and to determine the antimicrobial resistance profiles of these microorganisms by gradient-test method. Materials and Methods: The study included 368 clinical specimens sent for anaerobic culture between April 2017 and April 2018. Samples were incubated using anaerobic culture techniques and the isolates obtained were identified by MALDI-TOF mass spectrometry and phenotypic methods. Antimicrobial resistances of the isolates against chloramphenicol, metronidazole, penicillin G, imipenem and cefoxitin were determined by gradient test method. Results: A total of 104 anaerobic bacteria were isolated from 73 (19.8%) samples; the most frequently isolated anaerobic bacteria were Bacteroides (n=16), Actinomyces (n=15), Prevotella (n=12), Cutibacterium (n= 12) and Peptoniphilus (n=8) species. Antibiotic susceptibility testing was performed for 65 isolates. Metronidazole resistance among gram-positive bacilli, gram-positive cocci and gram-negative bacteria was found as 96.2%, 61.1% and 33.3%, respectively. About 15.4% of gram-positive bacilli and 14.3% of gram-negative bacilli were resistant against both cefoxitin and imipenem. Among gram-positive cocci, cefoxitin and imipenem resistance rates were found as 11.1% and 22.2%, respectively. Conclusion: This is the first study to present data on anaerobic bacteria detected in our region. High resistance to metronidazole and imipenem may be associated with increased use of metronidazole in outpatients and carbapenem in hospitalized patients. Determination of regional antibiotic susceptibility plays an important role in developing rational antibiotic use policies as well as guiding empirical treatments.