Escherichia coli from Human Wounds: Analysis of Resistance to β-Lactams and Expression of RND Efflux Pumps

Purpose: Resistance of pathogenic strains of Escherichia coli to beta-lactams, particularly to ampicillin, is on the rise and it is attributed to intrinsic and acquired mechanisms. One important factor contributing to resistance, together with primarily resistance mechanisms, is a mutation and/or an over-expression of the intrinsic efflux pumps in the resistance-nodulation-division (RND) superfamily. Among these efflux pumps, AcrA, AcrB, TolC, and AcrD play an important role in antimicrobial co-resistance, including resistance to beta-lactams.Materials and Methods: Twelve E. coli isolates obtained from patients' wounds and the control strain of E. coli ATCC 25922 were analyzed. The phenotypic resistance of these isolates to selected beta-lactams was assessed by determination of the minimal inhibitory concentration. Additionally, the prevalence of beta-lactamase genes (blaTEM, blaCTX-M, blaSHV, and blaAmpC) was screened by PCR. Realtime qPCR was used to determine the expression of the selected efflux pumps acrA, acrB, tolC, and acrD and the repressor acrR after the exposure of E. coli to ampicillin.Results: Phenotypic resistance to beta-lactams was detected in seven isolates, mainly to ampicillin and piperacillin. This was corroborated by the presence of at least one acquired bla gene in each of these isolates. Although E. coli strains varied in the expression of RND-family efflux pumps after the ampicillin exposure, their gene expression indicated that these pumps did not play a major role in the phenotypic resistance to ampicillin.Conclusion: Each E. coli isolate displayed unique characteristics, differing in minimum inhibitory concentration (MIC) values, prevalence of acquired blaTEM and blaCTX-M genes, and expression of the RND-family pumps. This together demonstrates that these clinical isolates employed distinct intrinsic or acquired resistance pathways for their defense against ampicillin. The prevalence and spread of ampicillin resistant E. coli has to be monitored and the search for ampicillin alternatives is needed.

Automated summary

Resistance to beta-lactams, particularly ampicillin, in pathogenic Escherichia coli is increasing due to intrinsic and acquired mechanisms, including mutations and over-expression of efflux pumps in the RND superfamily. This study analyzed isolates from patients' wounds and a control strain, finding that most isolates showed phenotypic resistance to ampicillin and piperacillin, with acquired bla genes present. However, the RND-family efflux pumps did not play a major role in the phenotypic resistance to ampicillin after exposure.