Antimicrobial Resistance Profiles and Clonal Relatedness of Canine and Feline Escherichia coli Pathogens Expressing Multidrug Resistance in the United States

Background Antimicrobial resistance is increasing among Escherichia coli isolates associated with spontaneous infection in dogs and cats. Objectives To describe E. coli resistance phenotypes and clonal relatedness and their regional prevalence. Animals Isolates of E. coli (n = 376) collected from dogs and cats in the United States between May and September 2005. Methods Isolates submitted from the South, West, Northeast, and Midwest regions of the United States were prospectively studied. Phenotype was based on E-test susceptibility to 7 antimicrobials. Isolates were classified as no (NDR), single (SDR), or multidrug resistance (MDR). Clonal relatedness was determined by pulsed-field gel electrophoresis (PFGE). Results One hundred and ninety-three (51%) isolates expressed resistance to at least 1 drug, yielding 42 phenotypes. SDR isolates (n = 84; 44%, 8 phenotypes), expressed resistance most commonly to amoxicillin (30%, n = 25) and least commonly to cefpodoxime (1%, n = 1). MDR isolates (n = 109; 56%, 31 phenotypes) were resistant to amoxicillin (96%, n = 105), amoxicillin-clavulanate (85%, n = 93), and enrofloxacin (64%, n = 70); 18% (n = 20) were resistant to all drugs tested. The frequency of MDR did not differ regionally (P = .066). MDR minimum inhibitory concentrations (MICs) were 6-fold higher than SDR MICs (P < .0001). Dendrograms of 91 isolates representing 25 phenotypes revealed 62 different PFGE profiles. Conclusions and Clinical Importance E. coli strains spontaneously infecting dogs and cats are genetically and phenotypically diverse. Given the current prevalence of MDR among clinical isolates of E. coli in United States, implementation of a robust surveillance program is warranted.