The cnf1 gene is associated to an expanding Escherichia coli ST131 H30Rx/C2 sublineage and confers a competitive advantage for host colonization

Epidemiological projections point to acquisition of ever-expanding multidrug resistance (MDR) by Escherichia coli , a commensal of the digestive tract acting as a source of urinary tract pathogens. We performed a high-throughput genetic screening of predominantly clinical E. coli isolates from wide geographical origins. This revealed a preferential distribution of the Cytotoxic Necrotizing Factor 1 (CNF1)-toxin encoding gene, cnf1 , in four sequence types encompassing the pandemic E. coli MDR lineage ST131. This lineage is responsible for a majority of extraintestinal infections that escape first-line antibiotic treatment and has known enhanced capacities to colonize the gastrointestinal tract (GIT). Statistical modeling uncovered a dominant global expansion of cnf1- positive strains within multidrug-resistant ST131 subclade H 30Rx/C2. Despite the absence of phylogeographical signals, cnf1 -positive isolates adopted a clonal distribution into clusters on the ST131- H 30Rx/C2 phylogeny, sharing a similar profile of virulence factors and the same cnf1 allele. Functional analysis of the cnf1 -positive clinical strain EC131GY ST131- H 30Rx/C2, established that a cnf1 -deleted EC131GY is outcompeted by the wildtype strain in a mouse model of competitive infection of the bladder while both strains behave similarly during monoinfections. This points for positive selection of cnf1 during UTI rather than urovirulence. Wildtype EC131GY also outcompeted the mutant when concurrently inoculated into the gastrointestinal tract, arguing for selection within the gut. Whatever the site of selection, these findings support that the benefit of cnf1 enhancing host colonization by ST131- H 30Rx/C2 in turn drives a worldwide dissemination of the cnf1 gene together with extended spectrum of antibiotic resistance genes. ### Competing Interest Statement The authors have declared no competing interest.