Granulomatous colitis in two French bulldogs unresponsive to fl uoroquinolone antimicrobials: a case report

Two cases of granulomatous colitis in two French bulldogs were found to be unresponsive to fluoroquinolones. The granulomatous colitis diagnosis was made on the basis of PAS-positive histiocytes in the lamina propria of the colonic mucosa in biopsy samples taken at colonoscopy. Remission of granulomatous colitis has been reported using fluoroquinolones leading to the idea that invasive Escherichia coli strains in the colonic mucosa are involved. Oral enrofloxacin (Baytril 150 mg, Bayer, Spain) at 10 mg/kg per day for eight weeks was prescribed to both dogs in this study. A first course of therapy resolved the problem in dog No. 1, which, however, was followed by relapse three months later without enrofloxacin response. No clinical remission was seen in dog No. 2 and 4.4 mg/kg marbofloxacin (Marbocyl P 20 mg, Vetoquinol, Spain) per day for 10 weeks was administered but without any response. From both dogs, biopsy samples from the colonic mucosa were taken during colonoscopy. Samples were homogenised for microbial culture in different agar media to identify invasive microbes. Escherichia coli were largely isolated and antibiotic sensitivity testing (MIC of E. coli to selected antimicrobials, CLSI 2013) was carried out. In both cases, E. coli was resistant to fluoroquinolones. In dog No. 1 E. coli was susceptible to amoxicillin-clavulanate, cefazolin, amikacin and gentamicin whereas in dog No. 2 it was susceptible to doxycycline and amoxicillin-clavulanate. Clinical remission was achieved in dog No. 1 with amoxicillin-clavulanate (Synulox 250 mg, Pfizer, Spain) therapy for eight weeks. No response was found in dog No. 2 with any of the antimicrobials alone or combined with metronidazole.