Treating infections caused by pathogenic Escherichia coli found outside the intestine (ExPEC), including urinary tract infections, is growing increasingly more challenging given the rise of antimicrobial resistance (AMR). AMR is predominant in certain E. coli strains, such as ST131, which have spread AMR globally. Now, using a gnotobiotic mouse model, researchers have shown that an MDR E. coli ST131 is capable of out-competing and displacing non-MDR E. coli from the gut in vivo.

This research is published in PLoS Biology in the paper, “Multi-drug resistant E. coli encoding high genetic diversity in carbohydrate metabolism genes displace commensal E. coli from the intestinal tract.”

“Antibiotic resistance has been hailed as one of the biggest health problems of our time by the World Health Organization, noted Alan McNally, PhD, professor at the Institute of Microbiology and Infection at the University of Birmingham, U.K. “There are further problems looming unless we get a better understanding of what is happening so that further drug resistance can be halted in its tracks.”

“Scientists have long questioned what makes certain types of E. coli successful multi-drug resistant pathogens,” McNally continues. “It seems that extra-intestinal pathogenic E. coli, which cause urinary tract and bloodstream infections, are particularly successful when it comes to developing resistance and are therefore especially tricky to treat. Our study provides evidence that certain types of E. coli are more prone to develop antibiotic resistance than others.”

The researchers first showed that both multi-drug resistant and non-resistant gut-dwelling E. coli were found to easily colonize a mammalian gut. In addition, using mice colonized with non-MDR E. coli strains, a challenge with MDR E. coli (either by oral gavage or co-housing with colonized mice) resulted in displacement and dominant intestinal colonization by MDR E. coli ST131.

The researchers went on to determine, using a functional pangenomic analysis of 19,571 E. coli genomes, that “carriage of AMR genes is associated with increased diversity in carbohydrate metabolism genes.”

Although some strains of E. coli are harmless, others can cause illness, including diarrhea, urinary tract infections, and often-fatal bloodstream infections. More severe infections are usually treated with antibiotics but the rise in multidrug resistance strains of E. coli is concerning. Previous work shows that multi-drug resistance alone is not sufficient to drive strains to complete dominance.

This study suggests that “independent of antibiotic selective pressures, MDR Ecoli display a competitive advantage to colonize the mammalian gut and points to a vital role of metabolism in the evolution and success of MDR lineages of Ecoli via carriage and spread.”

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