Contribution of the efflux pump AcrAB-TolC to the tolerance of chlorhexidine and other biocides in Klebsiella spp.

Abstract

Introduction. We are becoming increasingly reliant on the effectiveness of biocides to combat the spread of Gram-negative multi-drug-resistant (MDR) pathogens, including Klebsiella pneumoniae . It has been shown that chlorhexidine exposure can lead to mutations in the efflux pump repressor regulators SmvR and RamR, but the contribution of each individual efflux pump to biocide tolerance is unknown. Hypothesis. Multiple efflux pumps, including SmvA and AcrAB-TolC, are involved in increased tolerance to biocides. However, strains with upregulated AcrAB-TolC caused by biocide exposure are more problematic due to their increased MDR phenotype. Aim. To investigate the role of AcrAB-TolC in the tolerance to several biocides, including chlorhexidine, and the potential threat of cross-resistance to antibiotics through increased expression of this efflux pump. Methodology. Antimicrobial susceptibility testing was performed on K. pneumoniae isolates with ramR mutations selected for after exposure to chlorhexidine, as well as transposon mutants in components and regulators of AcrAB-TolC. RTPCR was used to detect the expression levels of this pump after biocide exposure. Strains from the globally important ST258 clade were compared for genetic differences in acrAB-TolC and its regulators and for phenotypic differences in antimicrobial susceptibility. Results. Cross-resistance to antimicrobials was observed following mutations in ramR. Exposure to chlorhexidine led to increased expression of acrA and its activator ramA, and transposon mutants in AcrAB-TolC have increased susceptibility to several biocides, including chlorhexidine. Variations in ramR within the ST258 clade led to an increase in tolerance to certain biocides, although this was strain dependent. One strain, MKP103, that had increased levels of biocide tolerance showed a unique mutation in ramR that was reflected in enhanced expression of acrA and ramA. MKP103 transposon variants were able to further enhance their tolerance to specific biocides with mutations affecting SmvA. Conclusions. Biocide tolerance in K. pneumoniae is dependent upon several components, with increased efflux through AcrAB-TolC being an important one.

Molecular patterns of clinically important fluoroquinolone resistance in multidrug-resistant Klebsiella pneumoniae isolates during nosocomial outbreaks in Shanghai, PR China

“…Mutations that result in altered OM permeability have also been shown to generate a fluoroquinolone resistance phenotype in K. pneumoniae [3,46,47]. AcrAB and OqxAB, two resistance-nodulation-division family pumps, made differential contributions to MDR and virulence [43,48,49]. In the absence of AcrAB, gyrase mutations fail to produce clinically relevant levels of resistance [50].…”

“…pneumoniae [3, 46, 47]. AcrAB and OqxAB, two resistance–nodulation–division family pumps, made differential contributions to MDR and virulence [43, 48, 49]. In the absence of AcrAB, gyrase mutations fail to produce clinically relevant levels of resistance [50].…”

Nanobiotics against antimicrobial resistance: harnessing the power of nanoscale materials and technologies

“…Increased efflux of chlorhexidine and other biocides through the efflux pump AcrAB-TolC has been identified as an important mechanism of AMR in Klebsiella spp. [14]. Tetracycline efflux pumps encoded by tetA, tetB, and tetK genes acquired through HGT provide resistance to tetracycline in both Gram-negative and Gram-positive bacteria [15].…”

Efflux-mediated tolerance to cationic biocides, a cause for concern?

“…For K. pneumoniae increased efflux is also observed following prolonged exposure to BAC [69] and, when a strain with a non-functional RND efflux pump, AcrAB-TolC, was compared to a genetically similar strain it showed reduced BAC and other cationic biocide tolerance [25]. When overexpressed the chromosomally located RND efflux pump OqxAB in K.…”

“…Whilst SmvA is potentially a major cationic biocide efflux transporter, there are other efflux pumps involved in cationic biocide tolerance in the Enterobacteriaceae . Mutations in regulators of acrAB-TolC are also observed following exposure to chlorhexidine [25, 50, 84]. For Klebsiella , Citrobacter and Enterobacter spp.…”