Three-decade epidemiological analysis of Escherichia coli O15:K52:H1

Abstract

The successful Escherichia coli O15:K52:H1 clonal group provides a case study for the emergence of multiresistant clonal groups of Enterobacteriaceae generally. Accordingly, we tested the hypotheses that, over time, the O15:K52:H1 clonal group has become increasingly (i) virulent and (ii) resistant to antibiotics. One hundred archived international E. coli O15:K52:[H1] clinical isolates from 100 unique patients (1975 to 2006) were characterized for diverse phenotypic and molecular traits. All 100 isolates derived from phylogenetic group D and, presumptively, sequence type ST393. They uniformly carried the F16 papA allele and papG allele II (P fimbria structural subunit and adhesin variants), iha (adhesin-siderophore), fimH (type 1 fimbriae), fyuA (yersiniabactin receptor), iutA (aerobactin receptor), and kpsM II (group 2 capsule); 85% to 89% of them contained a complete copy of the pap operon and ompT (outer membrane protease). Slight additional virulence profile variation was evident, particularly within a minor diarrhea-associated subset (biotype C). However, in contrast to the clonal group's fairly stable virulence profiles over the past 30+ years, during the same interval the clonal group members' antimicrobial resistance profiles increased by a mean of 2.8 units per decade (P < 0.001). Moreover, the numbers of virulence genes and resistance markers were positively associated (P = 0.046), providing evidence against antimicrobial resistance and virulence being mutually exclusive in these strains. Thus, the O15:K52:H1 clonal group has become increasingly resistant to antimicrobials while maintaining (or expanding) its virulence potential, a particularly concerning trend if other emerging multiresistant enterobacterial clonal groups follow a similar pattern.

FIG. 1.

Virulence gene tree for 100 isolates of Escherichia coli O15:K52:[H1]. The following genes are included: astA (enteroaggregative heat-stable enterotoxin), cvaC (microcin V), estA_p and estA_h (characteristic of ETEC; heat-stable toxin), fyuA (yersiniabactin receptor), hlyF (hemolysin F), hra (heat-resistant agglutinin), iha (adhesin-siderophore), iroN (siderophore receptor), ireA (siderophore receptor), iss (increased serum survival), iutA (aerobactin receptor), kpsM II (group 2 capsule), ompT (outer membrane protease T), pap (P fimbria operon; presumed to be complete [based on detection of papAH, papC, papEG, and papG allele II], unless listed as “partial”), tsh (temperature-sensitive hemagglutinin), and traT (serum resistance-associated protein).