Detection of the mecA Gene and Its Association With Antimicrobial Resistance Among Coagulase-Negative Staphylococci...

Introduction Coagulase-Negative Staphylococci (CoNS) have become major pathogens causing a variety of infections. Antimicrobial resistance, brought about by the acquisition of the mecA 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 mecA 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 mecA gene. Results Out of 100 CoNS isolates, Staphylococcus haemolyticus 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 mecA gene detection by rt-PCR, 82 (82%) isolates were positive for the mecA gene, and the rest were negative. Among the 82 (82%) mecA gene-positive isolates, seven (8.5%) were found to be cefoxitin sensitive, and among the 18 (18%) that were negative for the mecA gene, cefoxitin resistance was detected in five (27.7%) isolates by disk diffusion method. Both cefoxitin disk diffusion and mecA gene detection by rt-PCR were employed to detect methicillin resistance among the CoNS isolates. Conclusion The mecA gene was detected in 82 (82%) isolates. However, some mecA-positive CoNS were found to be susceptible to cefoxitin by the disk diffusion method, while some mecA-negative CoNS isolates were resistant. This suggests that no single diagnostic approach is capable of identifying methicillin resistance alone. Therefore, mecA gene detection must be implemented along with cefoxitin disk diffusion to make accurate and early therapeutic decisions.