THE IMMUNOHISTOLOGICAL DIAGNOSIS OF ESCHERICHIA-COLI O157-H7 COLITIS - POSSIBLE ASSOCIATION WITH COLONIC ISCHEMIA

Objective: E. coli O157:H7 may cause hemorrhagic colitis resembling is chemic colitis. Diagnosis is usually made by finding sorbitol-negative colonies on MacConkey agar that react with O157 and H7 antisera. Most ischemic colitis is idiopathic, but some may be caused by E. coli O15 7:H7, inasmuch as this organism can produce fibrin thrombi in colon va sculature. The objectives of this study were to determine whether E. c oli O157:H7 infection can be diagnosed retrospectively from paraffin b locks of colon sections and whether an association exists between E. c oli O157:H7 infection and colonic ischemia. Methods: Paraffin-embedded sections of normal colon (n = 2) and various colitides [ischemic (n = 11), E. coli O157:H7 (n = 2), IBD (n = 8) and pseudomembranous (n = 3 )] were used. Sections were deparaffinized, rehydrated, incubated with 3% peroxide in methanol, rinsed, and incubated with peroxidase-labele d antibody isolated from goats immunized with whole E. coli 0157: H7. Sections were stained with peroxidase chromagen reagent and countersta ined with hematoxylin. Coarse, granular, orange-brown staining was con sidered positive. To determine the localization of the chromagen depos its, three cases that stained positive, including one of the culture-p roved E. coli 0157:H7 colitis and two of colonic ischemia, were proces sed for electron microscopy. Results: Both cases (100%) of E. coli O15 7:H7 colitis and three of 11 (27.3%) cases of ischemic colitis stained positive by light microscopy. In one culture-proved case, electron mi croscopy demonstrated staining of bacillary structures; in two cases o f colonic ischemia, extensive deposits of chromagen material were pres ent that were associated neither with inflammatory cells nor with bact erial forms. Conclusions: Immunoperoxidase staining of archival sectio ns may be used to diagnose E. coli 0157:H7 infection. An etiological r ole for this organism is possible in some cases of colonic ischemia. ( C) 1998 by Am. Cell. of Gastroenterology.