Escherichia coli-induced granulomatous colitis in a cat

CASE SUMMARY: A 10-year-old castrated male domestic shorthair cat presented with a 6 month history of diarrhoea that responded poorly to medical treatment. Ultrasonography revealed moderate thickening of the colonic wall (4.8 mm) and right colic and jejunal lymphadenomegalies. Endoscopic examination revealed partial circumferential narrowing of the transverse colon and friable colonic mucosa with multiple haemorrhagic regions. Histopathological and immunohistochemical examinations revealed a large number of Escherichia coli phagocytosed by periodic acid–Schiff-positive macrophages. Bacterial culture also yielded enrofloxacin-sensitive E coli. The cat was initially treated with prednisolone, which resulted in little improvement. Following histopathological examination and bacterial culture, treatment with enrofloxacin was commenced. Antibacterial therapy resulted in remission of the diarrhoea and an increase in body weight within 14 days. RELEVANCE AND NOVEL INFORMATION: Granulomatous colitis (GC) or histiocytic ulcerative colitis has been rarely described in cats. There has only been one previously published case study involving a cat, and the aetiology remains largely unknown. The current article describes the regression of E coli-related GC following antibacterial treatment in a cat. Clinical signs, histopathological appearance and response to enrofloxacin were similar to those in canine GC. The current findings suggest that E coli also plays an important role in the development of feline GC.