Energy-dependent efflux overexpression and altered outer membrane permeability (influx) can promote multidrug resistance (MDR). The present study clarifies the regulatory pathways that control membrane permeability in the pandemic clone Escherichia coli sequence type 131 (ST131) and evaluates the impact of efflux and influx modulations on biofilm formation, motility, and virulence in the Caenorhabditis elegans model. Mutants of two uropathogenic E. coli (UPEC) strains, MECB5 (ST131; H30-Rx) and CFT073 (ST73), as well as a fecal strain, S250 (ST131; H22), were in vitro selected using continuous subculture in subinhibitory concentrations of ertapenem (ETP), chloramphenicol (CMP), and cefoxitin (FOX). Mutations in genes known to control permeability were shown for the two UPEC strains: MECB5-FOX (deletion of 127 bp in marR; deletion of 1 bp and insertion of an IS1 element in acrR) and CFT073-CMP (a 1-bp deletion causing a premature stop in marR). We also demonstrated that efflux phenotypes in the mutants selected with CMP and FOX were related to the AcrAB-TolC pump, but also to other efflux systems. Alteration of membrane permeability, caused by underexpression of the two major porins, OmpF and OmpC, was shown in MECB5-ETP and mutants selected with FOX. Lastly, our findings suggest that efflux pump-overproducing isolates (CMP mutants) pose a serious threat in terms of virulence (significant reduction in worm median survival) and host colonization. Lack of porins (ETP and FOX mutants) led to a high level of antibiotic resistance in an H30-Rx subclone. Nevertheless, this adaptation created a physiological disadvantage (decreased motility and ability to form biofilm) associated with a low potential for virulence.
Uropathogenic Escherichia coli (UPEC) is the leading causative agent of urinary tract infection (UTI) in both communities and hospitals worldwide (1). The therapeutic management of UTI is particularly problematic because of the increasingly widespread resistance to all classes of antibiotics, including in communityacquired infections (2). With the dissemination of the novel CTX-M family, E. coli has become the species most frequently associated with the production of extended-spectrum -lactamase (ESBL) (3). In 2008, a globally disseminated and multidrugresistant (MDR) clone of E. coli O25b:H4-ST131 was identified in clinical samples from three continents (4). Since this first description, sequence type 131 (ST131) was shown to be a successful clone, causing the majority of MDR E. coli infections while exhibiting multiple virulence factors (5, 6). Moreover, it was described as one of the most prevalent clones among phylogenetic group B2 in the digestive carriage of healthy subjects in France (7). Within the ST131 group, various subclonal lineages have been identified. Indeed, a dominant subclone named H30-Rx has extensively expanded. This subgroup harbors allele 30 of fimH, the type 1 fimbrial adhesin gene, and is associated with both bla CTX-M-15 carriage and fluoroquinolone (FQ) resistance by specific topoi...