Transcriptional Response of vanB Operon in Staphylococcus aureus Against Vancomycin and Teicoplanin Stress

Staphylococcus aureus is a global pathogen and is responsible for causing severe life-threatening infections. The current study was designed to investigate transcriptional expression of different core, regulatory, and accessory genes within van B operon under differential exposure of vancomycin and teicoplanin. Four isolates selected for the study, were confirmed to harbour van B gene in which three isolates showed MIC breakpoint above 16 µg/ml and one isolate above 8 µg/ml against vancomycin while teicoplanin showed higher MIC breakpoint as compared to vancomycin. Antibiotic susceptibility results showed that these isolates were susceptible towards imipenem and linezolid. Transcriptional expressional analysis of the core gene of van B operon showed that expression of van B is increased under vancomycin stress but is inversely proportional to increase in the concentration of the vancomycin while under teicoplanin stress the expression of van B showed no significant pattern. Similar expressional pattern was found for van H gene for both the glycopeptides. In case of van X, expression was significantly increased at 1 µg/ml exposure of vancomycin, however, no pattern could be observed in case of teicoplanin stress. In case of regulatory gene, van R, significant increase in expression was observed under vancomycin and teicoplanin stress of 1 µg/ml, however van S, showed significant increase in the expression under 1 µg/ml of vancomycin. The accessory gene, van Y showed marginal increase in expression under both the antibiotic, while in case of van W, the expressional pattern was found to be inversely proportional to the increasing antibiotic concentration.