GENOMIC COMPARISONS AND SHIGA TOXIN PRODUCTION AMONG ESCHERICHIA-COLIO157-H7 ISOLATES FROM A DAY-CARE-CENTER OUTBREAK AND SPORADIC CASES IN SOUTHEASTERN WISCONSIN

Contour-clamped homogeneous electric field pulsed-field gel electropho resis (CHEF-PFGE) was used to compare Wisconsin isolates of Escherichi a coli O157:H7, including 39 isolates from a 1994 day care center outb reak, 28 isolates from 18 individuals from the surrounding geographic area with sporadic cases occurring during the 3 months before the outb reak, and 3 isolates, collected in 1995, from patients with hemolytic- uremic syndrome (HUS) who were from eastern Wisconsin counties other t han those inhabited by the day care center : and sporadic-case individ uals. The technique df CHEF-PFGE using XbaI identified seven highly re lated restriction endonuclease digestion profiles (REDPs) (93 to 98% s imilarity) among the 39 day care center isolates and nine XbaI REDPs ( 63 to 93% similarity) among the 28 isolates from sporadic-case individ uals, including REDP 33, which was exhibited by both day care and spor adic-case isolates. PFGE analyses of sequential E. coli O157:H7 isolat es from symptomatic day care center attendees revealed that the REDPs of 25 isolates from eight patients were indistinguishable whereas the REDPs of 2 of 6 isolates from two patients differed slightly (93 to 95 % similarity). The REDPs of the three isolates from 1995 HUS patients were 78 to 83% similar, with REDP 26 being exhibited by one HUS-associ ated isolate and an isolate from one day care attendee who did not dev elop HUS. The genes for both Shiga toxins I and II (stx(1) and stx(2), respectively) were detected in all but one isolate (sporadic case), a nd Shiga toxin production by the day care center isolates was not sign ificantly different from that of the other isolates, including the thr ee HUS-associated isolates. Analyses of E.coli O157:H7 isolates from b oth the day care center outbreak and sporadic cases by CHEF-PFGE permi tted us to define the REDP variability of an outbreak and geographic r egion and demonstrated that the day care center outbreak and a HUS cas e in 1995 were caused by E. coli O157:H7 strains endemic to eastern Wi sconsin.