Abstract
Antibiotic resistance is an emerging public health issue. Plasmids are one of the popular carriers to disseminate resistance genes among pathogens. However, the response of plasmid-carrying bacteria to antibiotic treatment and how these bacteria evolve to increase their resistance remain elusive. In this study, we conjugated plasmid pNDM-HK to E. coli J53 recipient cells and selected survivors using different concentrations of the broad spectrum antibiotic meropenem. After selection, transconjugants conferred varying minimum inhibitory concentrations with respect to carbapenems. We sequenced and compared the transcriptomes of transconjugants that exhibited distinct carbapenem susceptibilities, and found that the loss of outer membrane proteins led to antibiotic resistance. Moreover, we identified a novel mutation, G63S, in transcription factor OmpR which moderates the expression of outer membrane proteins. The loss of porins was due to incapability of phosphorylation, which is essential for porin transcription and carbapenem resistance. We also characterized other genes that are regulated by ompR in this mutant, which contributed to bacterial antibiotic resistance. Overall, our studies suggest antibiotic pressure after conjugation might be an alternative pathway to promote antimicrobial resistance.
Highlights
Development of antibiotic resistance among Enterobacteriaceae has become a worldwide health issue[1]
In order to interpret the effect of antibiotic on selection process, the plasmid was firstly conjugated from the clinical isolate (E.coli, HK-01) to E.coli J53 and selected with four different concentrations of meropenem
Previous studies focused on the concentration and duration of antibiotic treatment that induce bacterial resistance[37,38] as well as the influence of antibiotic exposures to horizontal gene transfer, in particular their effects on bacterial conjugation[15,39]
Summary
Development of antibiotic resistance among Enterobacteriaceae has become a worldwide health issue[1]. Clinical isolates with carbapenem resistance are often associated with porin loss[11,12]. In order to understand the effect of antibiotics on bacteria carrying pNDM-HK, we conjugated pNDM-HK to E. coli J53 from a clinical isolate and selected using different concentrations of meropenem. Transconjugants selected by higher dosage of meropenem exhibited stronger carbapenem resistance. Transcriptomic analysis of these isogenic transconjugants indicated the development of stronger resistance was attributed to a novel point mutation G63S on the porin transcription factor, ompR, leading to the loss of porin. Our findings highlighted the importance of antibiotic selective pressure to bacterial physiology and their manipulations on gene expression for further developing stronger antibiotic resistance strains
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