Escherichia coli Infection: Coliform Typhlocolitis

A syndrome resembling C. rodentium and Helicobacter spp. colonic hyperplasia in immunodeficient mice has been associated with an atypical, non-lactose-ferment- ing E. coli.

Epizootiology and Pathogenesis

Large intestinal hyperplastic lesions have been observed primarily in young adult triple-deficient N:NIH(S)III (homozygous for nu, xid, bg) and to a lesser extent double-deficient mice.

Pathology

Mice are depressed, with perianal fecal staining. Gross necropsy findings are limited to mild to moderate seg­mental thickening of colon or cecum (Fig. 1.57) and

FIG. 1.57. Hyperplastic colitis due to Escherichia coli infection in a SCID mouse. Note the segmental thickening of the colon (arrows), unlike the involvement of the descending colon in mice infected with Citrobacter freundii and diffuse involvement in mice infected with Helicobacter spp.

occasional blood-tinged feces. Microscopic findings con­sist of mucosal hyperplasia in one or all segments of colon, with variable inflammation and erosion similar to C. freundii. Coliform bacteria are present in the gut lumen, attached to the surface, and within enterocytes of superficial mucosa of both small and large intestine.

Diagnosis

Segmental hyperplastic lesions in the colon and cecum of immunodeficient mice and isolation of atypical E. coli are required to confirm the diagnosis. The causative agent is non-lactose-fermenting, an unusual feature of E. coli. Differential diagnoses must include hyperplastic typhlocolitis caused by C. rodentium (which ferments lactose and is pathogenic in immunocompetent mice), Helicobacter spp., and enterotropic MHV in immuno­deficient mice. Unlike C. rodentium, which invariably affects descending colon, E. coli lesions are segmental and usually affect other portions of the colon.