Prevalence of Anaerobic Bacteria in Surgical Site Infections in a Tertiary Care Hospital

Background Surgical site infections (SSIs) are important postoperative complications associated with prolonged hospitalization, increased antimicrobial exposure and higher healthcare costs. Anaerobic bacteria are recognized contributors to SSIs but are often underdetected in routine laboratory practice due to challenges in specimen collection, transport and culture. This study aimed to determine the prevalence of anaerobic bacteria in clinically suspected SSIs and to describe the distribution of anaerobic isolates in monomicrobial and polymicrobial infections. Methods A prospective cross-sectional study was conducted in the Department of Microbiology at a tertiary care teaching hospital in Kanchipuram, India, from November 2024 to September 2025. A total of 72 postoperative patients with clinical suspicion of SSI were included. Appropriate wound specimens were processed for aerobic and anaerobic culture using standard microbiological methods. Anaerobic isolates were identified to the genus level by phenotypic disc-based and biochemical methods. Data were analyzed using IBM SPSS Statistics for Windows Version 29.0 and summarized using descriptive statistics. Results Anaerobic organisms were recovered from 22/72 specimens (30.5%). Among anaerobic culture-positive cases, polymicrobial infection was more common than monomicrobial infection, occurring in 16/22 (72.7%) and 6/22 (27.3%) cases, respectively. Bacteroides spp. were the most frequent isolates, accounting for 11/22 (50.0%), followed by Prevotella spp. in 5/22 (22.7%) cases. Anaerobic culture-positive cases were most common in patients aged 41-60 years (9/22, 40.9%), in men (14/22, 63.6%), and in gastrointestinal surgery cases (10/22, 45.5%). Conclusions Anaerobic bacteria constituted a substantial component of SSI microbiology, particularly in gastrointestinal and polymicrobial postoperative wound infections. These findings support the routine consideration of anaerobic culture in clinically suspected deep or contaminated SSIs to improve etiological diagnosis and guide antimicrobial management.