Antimicrobial Resistance Impacts Clinical Outcome of Granulomatous Colitis in Boxer Dogs

• Published in: Journal of veterinary internal medicine 2010-07, Vol.24 (4), p.819-824
• Main Authors: Craven, M, Dogan, B, Schukken, A, Volkman, M, Chandler, A, McDonough, P.L, Simpson, K.W
• Format: Article
• Language: English
• Subjects: AIEC; ampicillin; Animals; Anti-Bacterial Agents - pharmacology; Anti-Bacterial Agents - therapeutic use; antibiotic resistance; Boxer (dog breed); chloramphenicol; ciprofloxacin; colitis; Colitis - drug therapy; Colitis - microbiology; Colitis - veterinary; Crohn's; Dog Diseases - microbiology; Dogs; Drug Resistance, Multiple, Bacterial; drug therapy; Enrofloxacin; Escherichia coli; Escherichia coli - drug effects; Escherichia coli Infections - microbiology; Escherichia coli Infections - veterinary; Female; genotype; Histiocytic; IBD; Male; medicine; minimum inhibitory concentration; mucosa; prospective studies; remission; rifampicin; tetracycline
• ISSN: 0891-6640; 1939-1676
• DOI: 10.1111/j.1939-1676.2010.0527.x

Background: Escherichia coli have recently been identified within the colonic mucosa of Boxer dogs with granulomatous colitis (GC). Eradication of invasive E. coli is associated with clinical and histological remission. Objectives: To determine antimicrobial susceptibility profiles of E. coli strains from GC and healthy dogs, and the association of antimicrobial resistance with clinical outcome. Animals: Fourteen Boxer dogs with GC and 17 healthy pet dogs. Methods: Prospective study: E. coli was cultured from GC biopsies and rectal mucosal swabs of healthy dogs. Individual strains were selected by phylogroup and overall genotype, determined by triplex- and random amplified polymorphic DNA-polymerase chain reaction respectively. Antimicrobial susceptibility was determined by broth microdilution minimal inhibitory concentration. Results: Culture yielded 23 E. coli strains from GC (1–3/dog, median 2) and 34 strains from healthy (1–3/dog, median 2). E. coli phylogroups were similar (P= .18) in GC (5A, 7B1, 5B2, 6D) and healthy (2A, 10B1, 15B2, 7D). Resistance to ampicillin, amoxicillin-clavulanate, cefoxitin, tetracycline, trimethoprim-sulfa (TMS), ciprofloxacin, and chloramphenicol was greater (P < .05) in GC (21–64%) than healthy (0–24%). Enrofloxacin resistant E. coli were isolated from 6/14 GC versus 0/17 healthy (P= .004). Of the enrofloxacin resistant cases, 4/6 were also resistant to macrophage-penetrating antimicrobials such as chloramphenicol, rifampicin, and TMS. Enrofloxacin treatment before definitive diagnosis was associated with antimicrobial resistance (P < .01) and poor clinical outcome (P < .01). Conclusions and Clinical Importance: Antimicrobial resistance is common among GC-associated E. coli and impacts clinical response. Antimicrobial therapy should be guided by mucosal culture and antimicrobial susceptibility testing rather than empirical wisdom.