Upregulation of AcrEF in Quinolone Resistance Development inEscherichia coliWhen AcrAB-TolC Function Is Impaired

Abstract

We studied mechanisms of drug resistance development in Escherichia coli strains lacking efflux pump components. E. coli K12 deletion mutants were subjected to increasing concentrations of ciprofloxacin (CIP) to determine the frequency of target gene mutations. We generated a series of mutants that were selected based on their minimum inhibitory concentrations (MICs) to CIP, as well as their corresponding point mutations in target genes. The mutants displayed a number of target modifications and, in particular, gyrA mutations altering codons Ser83Leu, Asp87Gly, and Asp87His as well as a change in parC at 78 (substitution of Gly for Asp). All these mutations were related to drug resistance. When exposed to CIP, mutants lacking efflux pump genes acrA and acrB demonstrated a low level of resistance that was because of point mutations in the target genes. High-level resistance was achieved with a 100- to 500-fold increase in expression of efflux pump genes acrE and acrF that compensated for the loss of AcrA and AcrB, and thus resulted in an obvious increase of CIP MIC. We demonstrate that an intact AcrAB-TolC efflux pump is crucial to the development of bacterial resistance. Its activity is complemented by expression of the alternative AcrEF efflux pump.

Identification of binding residues between periplasmic adapter protein (PAP) and RND efflux pumps explains PAP-pump promiscuity and roles in antimicrobial resistance

“…In addition these data further support the idea that the PAPs could be an effective target against which to develop efflux inhibitors because inactivation of them increased susceptibility to a range of antimicrobials; reduced the frequency at which mutants with other resistance mechanisms could be selected, and reduced virulence. However, we also found that AcrE over-expression could easily be selected for and phenotypically compensate for the loss of AcrA in Salmonella and selection for increased expression of homologous efflux systems has also been described in E. coli [16,57]. This suggests that inhibition of only a single efflux pump component, for example AcrA, may not be an effective strategy because homologous components can provide PAP function to the major pump AcrB.…”

Overexpression of OqxAB and MacAB efflux pumps contributes to eravacycline resistance and heteroresistance in clinical isolates of Klebsiella pneumoniae

“…The overexpression of the RND-type efflux pump AcrEF was shown to be associated with fluoroquinolone resistance in Salmonella enterica serovar Typhimurium 24 . A recent study by Zhang et al 25 observed that AcrEF upregulation contributes to quinolone resistance development in E . coli .…”

Evaluation of Eravacycline: A Novel Fluorocycline

“…For example, high levels of macA expression in some ERV‐resistant and heteroresistant K. pneumoniae isolates in this study suggest that the MacAB‐TolC pump, which is known to extrude macrolide antibiotics, may also play an important role in ERV nonsusceptibility . Overexpression of the RND‐type efflux pump, AcrEF, which has been associated with fluoroquinolone resistance in Salmonella enterica serovar Typhimurium and E. coli was also observed in two ERV‐resistant K. pneumonia isolates . Among a collection of A. baumannii isolates (68% meropenem‐resistant) with ERV MICs ranging from 0.06 to 4 mg/L, a significant correlation between ERV MIC and the expression of adeB was observed .…”