LABORATORY INVESTIGATION OF A MULTISTATE FOOD-BORNE OUTBREAK OF ESCHERICHIA-COLI O157-H7 BY USING PULSED-FIELD GEL-ELECTROPHORESIS AND PHAGE TYPING

Two hundred thirty-three isolates of Escherichia coli 0157:H7 were ana lyzed by both pulsed-held gel electrophoresis (PFGE) and bacteriophage typing. All 26 isolates from persons whose illness was associated wit h a recent multistate outbreak of E. coli 0157:H7 infections linked to the consumption of undercooked hamburgers and all 27 isolates from in criminated lots of hamburger meat had the same phage type and the same PFGE pattern. Twenty-five of 74 E. coli 0157:H7 isolates from Washing ton State and 10 of 27 isolates from other states obtained during the 6 months before the outbreak had the same phage type as the outbreak s train, but only 1 isolate had the same PFGE pattern. PFGE thus appeare d to be a more sensitive method than bacteriophage typing for distingu ishing outbreak and non-outbreak-related strains. The PFGE patterns of seven preoutbreak sporadic isolates and five sporadic isolates from t he outbreak period differed from that of the outbreak strain by a sing le band, making it difficult to identify these isolates as outbreak or non-outbreak related. Phage typing and PFGE with additional enzymes w ere helpful in resolving this problem. While not as sensitive as PFGE, phage typing was helpful in interpreting PFGE data and could have bee n used as a simple, rapid screen to eliminate the need for performing PFGE on unrelated isolates.