Escherichia coli belonging to ST131 rarely transfers bla ctx-m-15 to fecal Escherichia coli.

Abstract

BackgroundExtended spectrum beta-lactamase (ESBL)-producing Escherichia coli (E. coli) causing urinary tract infections often belong to sequence type 131 (ST131), serotype O25, carrying blaCTX-M-15.AimThe main aim of this study was to examine the conjugational frequencies of E. coli with plasmids carrying blaCTX-M-15 to E. coli isolates from the fecal flora of healthy humans to determine whether ST131 is more likely to uptake or donate ESBL resistance compared to other E. coli clones.Methods Donors and recipients were all clinical isolates and did not harbor plasmids with identical incompatibility groups (Inc-groups) based on in silico analyses of Inc-groups and restriction/modification systems (R/M-systems). The in vitro conjugation experiments were performed as filter conjugation with verification of transconjugants by random amplified polymorphic DNA (RAPD) PCR and blaCTX-M-15 PCR.ResultsThe frequencies of conjugation with blaCTX-M-15-carrying plasmids were found to be very rare with detectable conjugation frequencies in the range of 4x10−9–7x10−7 transconjugants/recipient. Recipients of O25/ST131 type yielded significantly lower conjugation frequencies compared to recipients of other O-types (P=0.004). The applied ST131/O25 donors did not yield detectable levels of transconjugants regardless of the applied recipient. Presence of sub-MIC levels of ampicillin increased plasmid transfer frequencies x100 fold (P=0.07).ConclusionThe results indicate that blaCTX-M-15 is rarely transferred by conjugation to E. coli isolates of the intestinal flora, even when the gene is plasmid-borne.