Associations between multidrug resistance, plasmid content, and virulence potential among extraintestinal pathogenic and commensal Escherichia coli from humans and poultry

Abstract

The emergence of plasmid-mediated multidrug resistance (MDR) among enteric bacteria presents a serious challenge to the treatment of bacterial infections in humans and animals. Recent studies suggest that avian Escherichia coli commonly possess the ability to resist multiple antimicrobial agents, and might serve as reservoirs of MDR for human extraintestinal pathogenic Escherichia coli (ExPEC) and commensal E. coli populations. We determined antimicrobial susceptibility profiles for 2202 human and avian E. coli isolates, then sought for associations among resistance profile, plasmid content, virulence factor profile, and phylogenetic group. Avian-source isolates harbored greater proportions of MDR than their human counterparts, and avian ExPEC had higher proportions of MDR than did avian commensal E. coli. MDR was significantly associated with possession of the IncA/C, IncP1-α, IncF, and IncI1 plasmid types. Overall, inferred virulence potential did not correlate with drug susceptibility phenotype. However, certain virulence genes were positively associated with MDR, including ireA, ibeA, fyuA, cvaC, iss, iutA, iha, and afa. According to the total dataset, isolates segregated significantly according to host species and clinical status, thus suggesting that avian and human ExPEC and commensal E. coli represent four distinct populations with limited overlap. These findings suggest that in extraintestinal E. coli, MDR is most commonly associated with plasmids, and that these plasmids are frequently found among avian-source E. coli from poultry production systems.

FIG. 1.

Proportions (%) of isolate sources (y axis) relative to number of resistance phenotypes possessed (x axis). Each bar depicts the total source distribution of isolates relative to number of phenotypic resistances possessed.

FIG. 2.

Most prevalent antimicrobial resistance profiles among the 2202 Escherichia coli study isolates. The X-axis depicts the number of isolates possessing a given profile, using a stacked-bar presentation. Profiles with more than fifteen isolates were included.

FIG. 3.

Principal coordinates analysis of 2202 human and avian Escherichia coli isolates based on 67 traits, grouped by source of isolation. The analysis included antimicrobial susceptibility, plasmid replicon content, phylogenetic group, and virulence gene content. Data shown are the axis 1-versus-axis 2 plot. The axis 1-versus-axis 3 and axis 2-versus-axis 3 plots yielded similar findings (not shown).