Detection of Methicillin and Inducible Clindamycin Resistance in Staphylococcus aureus and coagulase-negative staphylococci Isolates from Surgical Site Infections: A Phenotypic Approach

Abstract

Background: The genus Staphylococci are among the most common pathogens implicated in surgical site infection (SSIs). While S. aureus is a well-recognized virulent organism, coagulase-negative staphylococci (CoNS) are often dismissed as contaminants; however, their role as opportunistic pathogens, particularly in hospitalized and immunocompromised patients, is increasingly acknowledged. This study aimed to compare the prevalence, antimicrobial resistance patterns, and virulence characteristics of S. aureus and CoNS isolated from SSIs.

Methods: A cross-sectional study was conducted comprising of 178 clinical isolates obtained from surgical site infections. Standard microbiological and biochemical methods were employed for identification, while antibiotic susceptibility testing was conducted using the modified Kirby-Bauer disc diffusion method in accordance with CLSI guidelines. Methicillin resistance was determined using cefoxitin discs, and inducible clindamycin resistance was detected using the D-test.

Results: Out of 178 staphylococcal isolates, 125 (70.2%) were S. aureus and 53 (29.8%) were CoNS. Methicillin resistance was detected in 30.4% of S. aureus and 34.0% of CoNS isolates. Inducible clindamycin resistance (D-test positivity) was observed in 9.1% of CoNS isolates, while none 0.0% of S. aures tested positive to D-test.

Conclusion: The study highlights a considerable burden of methicillin resistance among both S. aureus and CoNS isolates from SSIs, with CoNS showing slightly higher resistance rates. While inducible clindamycin resistance was present in CoNS, it was absent among MRSA isolates. These findings underscore the importance of routine antimicrobial susceptibility testing, including D-test screening, to guide appropriate therapeutic interventions and infection control strategies in surgical settings.

Keywords: Staphylococcus aureus, CoNS, surgical site infections, MRSA, methicillin resistance, D-test, clindamycin resistance.