Frequency of macrolide resistance gene msrA in clinically isolated erythromycin resistant Staphylococcus aureus strains from a tertiary care setting in Sindh, Pakistan

Background: The gene msrA is an efflux pump that encodes proteins causing macrolide resistance in different organisms. Macrolide resistance in Staphylococcus aureus is an emerging clinical challenge. The msrA efflux pump gene plays a significant role in mediating this resistance, making its local prevalence clinically relevant. Objectives: To determine the frequency of the msrA gene among clinically isolated erythromycin-resistant Staphylococcus aureus strains. Methods: This was a cross-sectional study carried out at the Department of Microbiology, Dow Diagnostic Research and Reference Laboratory, Karachi, Pakistan from 1st January 2018 to 31st January 2019. The frequency of msrA gene was determined in clinically isolated erythromycin resistant Staphylococcus aureus (S. aureus) strains. The study was reviewed and approved by the Institutional Review Board (IRB) of Dow University of Health Sciences. A total of 40 (n=40) erythromycin resistant S. aureus strains were isolated from the clinical samples and were obtained according to standard procedures. Antibiotic sensitivity was done as per Clinical and Laboratory Standards Institute (CLSI) guidelines. Resistant isolates were stored in Brain Heart Infusion Broth (BHI) and Polymerase Chain Reaction (PCR) were performed to detect the presence of msrA genes. Results: The frequency of msrA was 70% in clinically isolated erythromycin-resistant S. aureus strains. Conclusion: Based on the results, it was concluded that msrA is a significant contributor to the macrolide resistance in locally isolated clinical strains. A major clinical implication of this finding could be the use of efflux pump inhibitors with the macrolides may increase the sensitivity of the bacteria to the drugs, with favorable clinical outcomes.