Screening for mecA and mecC Gene Carriage among Clinical Isolates of Methicillin Resistant Staphylococcus aureus at a Tertiary Care Hospital: A Cross-sectional Study

Abstract

Introduction: Staphylococcus aureus (S. aureus) has emerged as one of the most important human pathogen, and has been a leading cause of hospital and community acquired infections. Methicillin-Resistant Staphylococcus aureus (MRSA) carrying the mecA gene is resistant to the majority of β-lactam antibiotics. In 2007, a new S. aureus strain harboring mecA gene homologue, mecC, was found in England which posed diagnostic problems. Accurate and rapid detection of MRSA is required for effective treatment. Aim: To screen for mecA and mecC genes among methicillin resistant isolates of S. aureus using conventional Polymerase Chain Reaction (PCR) and to associate their presence to Kirby-Bauer disc diffusion and automated Vitek 2 methods. Materials and Methods: This cross-sectional observational study was conducted in the Department of Microbiology, Victoria hospital, Bangalore Medical College and Research Institute, Bengaluru, Karnataka, India, from July to October 2019. A total of 60 duplicate S. aureus samples were obtained from various clinical samples during the study period. Isolates were subjected to antibiotic susceptibility by cefoxitin disc diffusion and automated Vitek-2. Isolates were screened for mecA and mecC gene carriage using conventional PCR. Descriptive statistics was used for the comparison of data and appropriate statistical charts were used to present the data. Results: Among 60 S. aureus isolates, 41 (68.33%) of them were considered MRSA by conventional Disc Diffusion Method (DDM) and 48 (80%) of them were considered MRSA by automated Vitek-2. By conventional PCR only 34 (56.67%) isolates carried the mecA gene and none of the clinical isolates possessed the mecC gene. Conclusion: An overall MRSA prevalence of 56.67% was observed by PCR in present study. The mecC gene was not detected in any of the S. aureus isolates. Present study indicates the presence of mecA and mecC negative phenotypically identified MRSA isolates. Rather than absolute dependence on the mecA gene as the defining standard in determining MRSA, alternative mechanisms of resistance-presence of mecC, mecB genes, hyperproduction of b-lactamase; can potentially be a knowledge trove for researchers to delve into.

Keywords

• antibiotic resistance
• cefoxitin disc diffusion
• polymerase chain reaction
• vitek-2