RAPID DIAGNOSIS OF ENTEROHEMORRHAGIC ESCHERICHIA-COLI O157H7 DIRECTLYFROM FECAL SPECIMENS USING IMMUNOFLUORESCENCE STAIN

Serotype O157:H7 is most frequently encountered among verotoxin-produc ing Escherichia coli. Most laboratories use MacConkey-sorbitol agar as a screening medium. Presumptive identification of sorbitol-negative c olonies is then accomplished by latex agglutination or biochemical tes ts with serologic confirmation, which requires 18-36 hours for complet ion. This study attempted to detect E coli O157:H7 directly from stool specimens by direct immunofluorescence (DIF) antibody staining to pro vide quicker turnaround (< 2 hours). A total of 336 abnormal fecal sam ples (bloody, watery, semi-liquid, or mucoid) were examined by this me thod. Results were compared with those of culture. Direct immunofluore scence antibody staining of the direct fecal smear detected all isolat es of E coli O157 that were recovered by culture, including nonmotile strains, strains possessing the H7 flagellar antigen, and one strain w ith a flagellar antigen other than H7. Optimum results were achieved w hen specimens were pretreated with 5% bleach and centrifugation. No fa lse-negative results were obtained with bleach-pretreated stool sample s.