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Background: Extraintestinal infections caused by multidrug-resistant (MDR) Escherichia coli and Enterobacter are becoming more common in veterinary medicine.Objective Methods: Retrospective case series assembled from hospital records data, including clinical history before 1st MDR isolation and treatment outcome. Identity and antimicrobial susceptibility profiles were confirmed by standard microbiological techniques for 57 isolates.Results: Most dogs had an underlying disease condition (97%), received prior antimicrobial treatment (87%), were hospitalized for !3 days (82%), and had a surgical intervention (57%). The urinary tract was the most common infection site (62%), and urinary catheterization, bladder stasis, or both were common among dogs (24%). Some dogs were treated with high doses of co-amoxyclavulanate (n 5 14) and subsequently recovered even though the isolates showed in vitro resistance to this antimicrobial. Other dogs were successfully treated with chloramphenicol (n 5 11) and imipenem (n 5 2).Conclusion and Clinical Importance: Predisposing disease condition, any prior antimicrobial use rather than a specific class of antimicrobial, duration of hospitalization, and type of surgical procedure might be risk factors for acquiring MDR extraintestinal infections. Whereas culture and sensitivity results can indicate use of last-resort antimicrobials such as imipenem for MDR infections, some affected dogs can recover after administration of high doses of co-amoxyclavulanate.

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The genetic determinants involved in reduced susceptibility to third-generation cephalosporins and aztreonam were identified in ten canine Enterobacter isolates associated with opportunistic infections in three veterinary hospitals in Brisbane, Australia. All isolates were evaluated by a combination of phenotypic (broth microdilution and disc susceptibility, modified disc diffusion and IEF) and genotypic (PFGE, plasmid analysis, Southern blot hybridization, bacterial conjugation, PCR and sequencing) methods to investigate genetic relatedness and to identify plasmid-mediated resistance genes, in particular b-lactamase genes responsible for extended-spectrum cephalosporin resistance. The ten canine isolates were genotypically diverse based on PFGE and belonged to either Enterobacter cloacae or Enterobacter hormaechei on the basis of 16S rRNA gene sequence analysis. Plasmid profiles were also diverse. Nine isolates contained a transmissible bla SHV-12 -carrying plasmid (~140 kb) that also conferred resistance to chloramphenicol, gentamicin, spectinomycin, tetracycline, trimethoprim and sulfonamides. In all plasmid-mediated extended-spectrum b-lactamase (ESBL)-producing isolates including transconjugants, bla SHV-12 was shown to reside in a~6.5 kb plasmid fragment. The remaining isolate that was not an ESBL producer possessed an AmpC b-lactamase gene (bla CMY-2 ) on ã 93 kb transmissible plasmid. This plasmid did not contain any other antimicrobial resistance genes. Additional plasmid-mediated b-lactamases identified in some isolates included bla TEM and bla . This is the first report of canine Enterobacter isolates containing transmissible plasmid-mediated bla SHV-12 and bla CMY-2 resistance genes. Therefore, Enterobacter isolated from opportunistic infections in dogs may be an important reservoir of plasmid-mediated resistance genes, which could potentially be spread to other members of the Enterobacteriaceae.