Inhibitor-Resistant TEM- and OXA-1-Producing Escherichia coli Isolates Resistant to Amoxicillin-Clavulanate Are More Clonal and Possess Lower Virulence Gene Content than Susceptible Clinical Isolates

Abstract

ABSTRACTIn a previous prospective multicenter study in Spain, we found that OXA-1 and inhibitor-resistant TEM (IRT) β-lactamases constitute the most common plasmid-borne mechanisms of genuine amoxicillin-clavulanate (AMC) resistance inEscherichia coli. In the present study, we investigated the population structure and virulence traits of clinical AMC-resistantE. colistrains expressing OXA-1 or IRT and compared these traits to those in a control group of clinical AMC-susceptibleE. coliisolates. All OXA-1-producing (n= 67) and IRT-producing (n= 45) isolates were matched by geographical and temporal origin to the AMC-susceptible control set (n= 56). We performed multilocus sequence typing and phylogenetic group characterization for each isolate and then studied the isolates for the presence of 49 virulence factors (VFs) by PCR and sequencing. The most prevalent clone detected was distinct for each group: group C isolates of sequence type (ST) 88 (C/ST88) were the most common in OXA-1 producers, B2/ST131 isolates were the most common in IRT producers, and B2/ST73 isolates were the most common in AMC-susceptible isolates. The median numbers of isolates per ST were 3.72 in OXA-1 producers, 2.04 in IRT producers, and 1.69 in AMC-susceptible isolates; the proportions of STs represented by one unique isolate in each group were 19.4%, 31.1%, and 48.2%, respectively. The sum of all VFs detected, calculated as a virulence score, was significantly higher in AMC-susceptible isolates than OXA-1 and IRT producers (means, 12.5 versus 8.3 and 8.2, respectively). Our findings suggest that IRT- and OXA-1-producingE. coliisolates resistant to AMC have a different and less diverse population structure than AMC-susceptible clinicalE. coliisolates. The AMC-susceptible population also contains more VFs than AMC-resistant isolates.