Determination of Antibiotic Susceptibility of Clostridium Species Isolated from Clinical Specimens

Objective: Clostridium species are clinically important anaerobic pathogens associated with severe infections; however, data on their antimicrobial susceptibility patterns in Türkiye remain limited. This study aimed to evaluate the antimicrobial susceptibility profiles of Clostridium species isolated from invasive clinical specimens and compare them with reported global resistance patterns.Methods: A total of 50 Clostridium spp. isolates representing 13 species were recovered between 2019 and 2024. Species identification was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Five species previously classified within the genus Clostridium but currently assigned to different genera were also included. Antimicrobial susceptibility testing was performed using the gradient diffusion method to determine minimum inhibitory concentrations (MICs) of ampicillin, ampicillin–sulbactam, vancomycin, metronidazole, clindamycin, and meropenem. Results were interpreted according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints.Results: The most frequently isolated species were Clostridium perfringens (n=15), C. paraputrificum (n=7), C. tertium (n=5), and C. sporogenes (n=5). All isolates were susceptible to metronidazole. High susceptibility rates were observed for ampicillin–sulbactam (90%) and vancomycin (88%); however, all C. innocuum isolates and most C. sporogenes isolates were resistant to vancomycin. Overall susceptibility to ampicillin was 78%, with resistance rates ≥40% in several species. Clindamycin showed the lowest activity (38% susceptibility), while meropenem resistance was detected in 48% of isolates.Conclusion: Metronidazole and ampicillin–sulbactam remain effective for empirical treatment of Clostridium infections in Türkiye. Vancomycin and ampicillin should be used cautiously, and clindamycin and meropenem should be avoided without susceptibility testing; species-specific resistance patterns should guide treatment decisions.