Investigation of transfer mechanism of conjugative plasmids harboring carbapenemase genes in uropathogenic escherichia coli

Abstract

The increase in UTI caused by E. coli is linked to an increase in plasmid-mediated MDR and has become a public health crisis worldwide. The increased incidence of infection caused by carbapenem-resistant pathogens has raised concerns recently. Hence, understanding the mechanisms underlying the rapid dissemination of carbapenem resistance is of great importance. In this project, a collection of ESBL-producing UPEC strains was characterized and selected as the recipients of the conjugative mating with carbapenem-resistant E. coli strains in an attempt to study the conjugative transfer dynamics of carbapenem-resistant plasmids. The genomic characterization of the UPEC strains isolated from a single centre revealed that globally high-risk ST131 isolates were the most prevalent among the UPEC collection. This finding underlined the wide spread of the MDR ST131 clones in UTI and in other infections caused by pathogenic E. coli. blaCTX-M β-lactamase was the most prevalent plasmid-borne ESBL during the study period, and all isolates harbored blaEC β-lactamases on their chromosome. The narrow host range IncF-type plasmids containing diverse IncF subtypes were most common and widely spread in the UPEC isolates. Multiple genes encoding various resistance traits were commonly found on these IncF plasmids. Indeed, in high-risk clones, a strong correlation existed between the presence of plasmid with ESBLs and MDR. The presence of plasmids with MDR was, in fact, clearly associated with high-risk clones. Diverse virulence factors associated with the pathogenesis of UTIs were found. The virulence scores of the domestic and international ST131 UPEC isolates were found to be similar. The blaIMP-4-carrying IncN and blaNDM-carrying plasmids were found to be conjugatively transferrable to various UPEC recipients without any fitness cost. The rapid spread of carbapenem resistance was not lineage-specific. The conjugative transfer frequencies of the blaIMP-4-carrying IncN and blaNDM-carrying plasmids were similar when acquired by a common recipient E. coli K12 strain. The increased transfer frequency of a blaIMP-4–carrying IncN plasmid with double copies of resistance and conjugation regions was driven by a phage-like plasmid. Thus, a novel positive interaction between the two plasmids resulted in enhanced transferability of the blaIMP-4-carrying IncN plasmid. Besides the known factors affecting the conjugative transfer frequencies of plasmids, this finding provided additional knowledge to the complex process of conjugation.