Molecular study of Chlorhexidine resistance in Methicillin Resistant Staphylococcus aureus

Abstract

Methicillin Resistant Staphylococcus aureus (MRSA) is a main cause of severe human infections. The aim of this study was to detect chlorhexidine resistance of MRSA by phenotypic and genotypic methods. Fifty MRSA strains were isolated from different hospitals of Mansoura University over a period of one year from December 2021 till November 2022. The antimicrobial susceptibility test was conducted by the disk diffusion method, except for vancomycin which was detected by minimum inhibitory concentration (MIC) determination using microdilution broth method. The MIC towards chlorhexidine (CHG) was determined by microdilution broth method. Qac genes (qacA/B1, qacA/B2, smr, and norA) were detected by Polymerase Chain Reaction (PCR). Transmission electron microscope was used for determination of cell-wall thickness of chlorhexidine susceptible and resistant strains. The results exhibited that the greatest resistance of the isolates was towards Penicillin (100%) and Ceftazidime (100%) and the greatest susceptibility was towards Vancomycin (72%). Decreased susceptibility to CHG at MIC ≥4 mg/L was in 24 isolates (48%). The highest detected genes were smr (100%), norA (50%), and qacA/B2 (45.8%), with a low prevalence of qacA/B1 (4.16%). It was found that the MRSA strain with high resistance to chlorhexidine had more thickened cell wall than that of the susceptible strain.