Antimicrobial resistance impacts clinical outcome of granulomatous colitis in boxer dogs.
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.


OBJECTIVE
To determine antimicrobial susceptibility profiles of E. coli strains from GC and healthy dogs, and the association of antimicrobial resistance with clinical outcome.


METHODS
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
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.
Craven
M
M
College of Veterinary Medicine, VMC 2001, Cornell University, Ithaca, NY 14853-9655, USA.
Dogan
B
B
Schukken
A
A
Volkman
M
M
Chandler
A
A
McDonough
P L
PL
Simpson
K W
KW
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000627:therapeutic use*; D003092:Colitis / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary*; D004283:Dog Diseases / Q000382:microbiology*; D004285:Dogs; D024901:Drug Resistance, Multiple, Bacterial; D004926:Escherichia coli / Q000187:drug effects; D004927:Escherichia coli Infections / Q000382:microbiology / Q000662:veterinary*; D005260:Female; D008297:Male
D000900:Anti-Bacterial Agents