Detection of the mecA Gene and Its Association With Antimicrobial Resistance Among Coagulase-Negative Staphylococci Isolated From Clinical Samples in a Tertiary Care Hospital: A Cross-Sectional Study

Introduction Coagulase-Negative Staphylococci (CoNS) have become major pathogens causing a variety of infections. Antimicrobial resistance, brought about by the acquisition of the <i>mec</i>A gene, further exacerbates this burden. This gene encodes the altered membrane-bound protein called penicillin-binding protein (PBP2a), which lowers the binding affinity for β-lactam antibiotics. The widespread distribution of this gene has led to the surge of methicillin-resistant CoNS (MR-CoNS). Therefore, this study aimed to detect the prevalence of the <i>mec</i>A gene and its correlation with antimicrobial resistance. Methods This was a cross-sectional observational study conducted over a period from January 2021 to May 2022 at a tertiary care hospital in Delhi, India. A total of 100 pure isolates of CoNS from various samples were included and identified at the species level using conventional methods and an automated Vitek-2 ID system (bioMérieux, Marcy-l'Étoile, France). Antibiotic susceptibility testing was performed using the Kirby-Bauer disk diffusion method, as per the Clinical and Laboratory Standards Institute (CLSI) 2020 guideline, with the following antibiotics: cefoxitin (30 μg), erythromycin (15 μg), cotrimoxazole (1.25/23.75 μg), tetracycline (30 μg), gentamicin (10 μg), and ciprofloxacin (5 μg). The minimum inhibitory concentration (MIC) for vancomycin was detected using the Epsilometer test (E-test). All of the 100 isolates were also subjected to real-time polymerase chain reaction (rt-PCR) for the detection of the <i>mec</i>A gene. Results Out of 100 CoNS isolates, <i>Staphylococcus haemolyticus</i> was the most commonly isolated, accounting for 44%. Cefoxitin was sensitive for only 20% of the isolates. Sensitivities for ciprofloxacin, cotrimoxazole, gentamicin, tetracycline, and erythromycin were 56%, 55%, 50%, 49%, and 25%, respectively. All isolates were sensitive to vancomycin. Out of 100 CoNS isolates that were subjected to <i>mec</i>A gene detection by rt-PCR, 82 (82%) isolates were positive for the <i>mec</i>A gene, and the rest were negative. Among the 82 (82%) <i>mec</i>A gene-positive isolates, seven (8.5%) were found to be cefoxitin sensitive, and among the 18 (18%) that were negative for the <i>mec</i>A gene, cefoxitin resistance was detected in five (27.7%) isolates by disk diffusion method. Both cefoxitin disk diffusion and <i>mec</i>A gene detection by rt-PCR were employed to detect methicillin resistance among the CoNS isolates. Conclusion The <i>mec</i>A gene was detected in 82 (82%) isolates. However, some <i>mec</i>A-positive CoNS were found to be susceptible to cefoxitin by the disk diffusion method, while some <i>mec</i>A-negative CoNS isolates were resistant. This suggests that no single diagnostic approach is capable of identifying methicillin resistance alone. Therefore, <i>mec</i>A gene detection must be implemented along with cefoxitin disk diffusion to make accurate and early therapeutic decisions.