Concomitant with the recent emergence of CTX-M-type extended-spectrum beta-lactamases
(ESBLs), Escherichia coli has become the enterobacterial species most affected by
ESBLs. Multiple locales are encountering CTX-M-positive E. coli, including specifically
CTX-M-15. To gain insights into the mechanism underlying this phenomenon, we assessed
clonality and diversity of virulence profiles within an international collection of
CTX-M-15-positive E. coli.
Forty-one ESBL-positive E. coli isolates from eight countries and three continents
(Europe, Asia and North America) were selected for study based on suspected clonality.
Phylogenetic group, ERIC2 PCR profile, O H serotype, AmpC variant and antibiotic susceptibility
were determined. Multilocus sequence typing (MLST) and PFGE provided additional discrimination.
Virulence potential was inferred by detection of 46 virulence factor (VF) genes.
Thirty-six (88%) of the 41 E. coli isolates exhibited the same set of core characteristics:
phylogenetic group B2, ERIC2 PCR profile 1, serotype O25:H4, AmpC EC6, ciprofloxacin
resistance and MLST profile ST131. By PFGE, the 36 isolates constituted one large
cluster at the 68% similarity level; this comprised 17 PFGE groups (defined at 85%
similarity), some of which included strains from different countries. The 36 isolates
exhibited highly (91% to 100%) similar VF profiles.
We describe a broadly disseminated, CTX-M-15-positive and virulent E. coli clonal
group with highly homogeneous virulence genotypes and subgroups exhibiting highly
similar PFGE profiles, suggesting recent emergence. Understanding how this clone has
emerged and successfully disseminated within the hospital and community, including
across national boundaries, should be a public health priority.