Clonal group distribution of fluoroquinolone-resistant Escherichia coli among humans and companion animals in Australia

Objectives: To determine the phylogenetic group distribution and prevalence of three major globally disseminated clonal groups [clonal group A (CGA) and O15:K52:H1, associated with phylogenetic group D, and sequence type ST131, associated with phylogenetic group B2] among fluoroquinolone-resistant extra-intestinal Escherichia coli isolates from humans and companion animals in Australia. Methods: Clinical extra-intestinal fluoroquinolone-resistant E. coli isolates were obtained from humans (n = 582) and companion animals (n  = 125), on Australia's east coast (October 2007–October 2009). Isolates were tested for susceptibility to seven antimicrobial agents, and for phylogenetic group, O type and clonal-group-specific single nucleotide polymorphisms by PCR. Results: The fluoroquinolone-resistant isolates were typically resistant to multiple agents (median of four). Analysis revealed that clonal group ST131 accounted for a large subset of the human isolates (202/585, 35%), but for a much smaller proportion of the companion animal isolates (9/125, 7.2%; P ≤ 0.001). In contrast, CGA and O15:K52:H1 were uncommon among both human (7.2%) and companion animal (0.8%) isolates. Conclusions: In Australia, a large proportion (42%) of recent fluoroquinolone-resistant extra-intestinal E. coli isolates from humans are represented by three major globally disseminated clonal groups, predominantly ST131, which by contrast is comparatively rare among fluoroquinolone-resistant E. coli from companion animals. In conjunction with Australia's ban on fluoroquinolone use in livestock, these results argue against a major domestic food animal or companion animal source for fluoroquinolone-resistant extra-intestinal E. coli among humans in Australia. However, both humans and companion animals are involved in the intercontinental emergence and dissemination of ST131.

Joanne L. Platell, Rowland N. Cobbold, James R. Johnson and Darren J. Trott