Inducible Clindamycin Resistance among Methicillin-Resistant <i>Staphylococcus aureus</i> Isolates in a Tertiary Care Hospital: A Phenotypic Detection

Background: Staphylococcus aureus is one of the most commonly isolated pathogens from various clinical specimens, and it is implicated in both community-acquired and healthcare-associated infections. It is an important member of the notorious ESKAPE group of pathogens. They are named so because they are infamous for their abilities to escape antimicrobial action by adopting various resistance mechanisms. Being the 2nd most commonly isolated bacterial species among them, S. aureus has its fair share of resistance mechanisms. Methicillin resistance is increasingly being reported worldwide, and S. aureus resistant to more than 2 classes of antibiotics is also rising alarmingly. Objective: To understand the susceptibility and resistance profile of S. aureus isolates with special focus on MRSA isolates and to identify inducible clindamycin resistance among them using CLSI-approved phenotypic detection methods. Methods: This was a descriptive cross-sectional study conducted in the Department of Microbiology, Coimbatore Medical College and Hospital, Coimbatore, Tamil Nadu, India, between December 2024 and February 2025. The study included 170 S. aureus isolates. Results: At the end of this study, the majority of S. aureus isolations were from pus samples at 55% followed by blood samples at 30%. Antimicrobial susceptibility testing of 170 isolates showed MRSA in 35.9% isolates. Resistance rates of 89% to ampicillin, 70% to gentamicin, 61% to ciprofloxacin and 53% to erythromycin were recorded, while the susceptibility rates were 100% to linezolid, 91% to doxycycline, 75% to cotrimoxazole, 62% to clindamycin. Inducible clindamycin resistance-ICR was detected by the D-test among 16% of isolates. 100% susceptibility towards vancomycin was established by performing a vancomycin screen agar. Conclusion: The results highlighted that MDR S. aureus were more common among MRSA isolates, and the need to look out for both constitutive and inducible clindamycin resistance, as clindamycin is favoured by many clinicians to counteract the toxins of S. aureus.