Expression of acrB and ramA in fluoroquinolone resistant mutants from multi-drug resistant Salmonella enterica serovar Haardt

Abstract

Aims: To identify the effect of elevation of resistance in multi-drug resistant Salmonella enterica serovar Haardt with reduced susceptibility to ciprofloxacin, a parental strain SAL59-FC-KF04 was exposed to fluoroquinolone. Sequence of quinolone resistance determining region (QRDR) was analysed and expression level of efflux pump related genes was compared between the parental strain and the derived mutants. Methods and Results: The molecular expression levels of efflux pump genes (acrB, acrF) and transcriptional regulatory genes (marA, ramA, robA and soxS) were quantified using qRT-PCR. For the confirmation of the impact of efflux pump on drug-resistance, efflux inhibition test and sequence analysis of QRDR were performed. Two mutants were obtained by point mutation on QRDR and the increased level of expression of acrB and ramA. Conclusions: As a result of in vitro exposure to fluoroquinolones for parental strain, elevated fluoroquinolone resistance and overexpression of acrB and ramA have been observed. One of the mutants combined with additional QRDR point mutation showed increase of resistance to fluoroquinolone and several antimicrobials in other classes. Significance and Impact of the Study: This study demonstrates how continuous usage of antimicrobials affects the increase of drug-resistance in Salmonella enterica induced by QRDR mutation and efflux pump related genes.