Phylogenetic grouping, antibiotic resistance profile, fluoroquinolone susceptibility and ST131 status of canine extra intestinal Escherichia Coli isolated from submissions to a veterinary diagnostic laboratory 2005-08

Fluoroquinolones (FQs) are a recommended treatment for Escherichia coli infections in companion animals, particularly in cases of resistance to other drug classes. In a retrospective study, 162 canine clinical E. coli isolates, obtained from veterinary diagnostic submissions (January 2005 - June 2008), were analyzed for phylogenetic group and antibiogram phenotype, using nine antimicrobials and enrofloxacin, ciprofloxacin, moxifloxacin and pradofloxacin minimum inhibitory concentrations (MICs), either in the absence or presence of an efflux pump inhibitor. The isolate susceptibility distribution was bimodal; a high proportion (141/162;87%) showed a sensitivity equivalent to wildtype E. coli (enrofloxacin MIC 0.004 - 0.06 μg/mL), while a minority (4/162;2%) showed reduced susceptibility (enrofloxacin MICs of 0.125 - 0.5 μg/mL), and the remainder (17/162;10%) yielding enrofloxacin MICs in the highlevel resistance range of ≥16 μg/mL. All FQ-resistant isolates were also multidrug-resistant. The majority of FQsensitive isolates belonged to phylogenetic group B2 (101/162;62%), and the majority of resistant isolates to group D (8/17;47%). A single resistant B2 isolate and three FQ-sensitive isolates were identified as ST131. Efflux pump activity contributed significantly to MICs for all FQs, except for ciprofloxacin, which may be attributable to its higher polarity compared to the other FQs. These findings confirm a low prevalence of FQ resistance in Australian canine E. coli isolates. Detection of a high moxifloxacin: low ciprofloxacin MIC efflux-associated phenotype (102/162;63%) amongst canine strains may indicate previous exposure to moxifloxacin selective pressure, providing more evidence of exchange of E. coli strains between humans and dogs. The presence of sensitive ST131 strains in the isolate collection does suggest, however, that resistant ST131 strains could potentially emerge under both human and veterinary antimicrobial selection pressure, a risk that could be mitigated by using the most active fluoroquinolone (i.e. pradofloxacin in dogs) against wild-type E. coli at mutant prevention concentrations.Joanne L, Platell, Darren J. Trott, Heinz-Georg Wetzstein, Micheal Leitner and Rowland N. Cobbol