Shiga toxin (Stx)-producing Escherichia coli O157 isolates (n = 123) were divided into groups according to origin, genotype (pulsed-field gel electrophoresis [PFGE] type, or ribotype), type
of Stx produced, or phage type (PT). The survival rate ([number of CFU after 24 h of drying/number of CFU before drying] × 100) for each isolate was determined in triplicate after drying on concrete
for 24.0 h. The overall mean survival rate among the 123 E. coli O157 isolates studied was 22.9%, but there was a wide range of responses to drying on concrete, with a minimum of 1.2% and a maximum
of 61.9% of the initial inocula being recovered after drying. Among the groups, those isolates that originated from cases of human disease were, on average, significantly more sensitive (P < 0.001)
to drying (with a mean survival rate of 15.3%) than isolates from the other three sources (with mean survival rates of 27.7, 26.0, and 22.9% for meats, bovine or ovine feces, and bovine hides, respectively).
When the isolates were grouped by genotype, three of the PFGE types were, on average, significantly more resistant to drying than two other PFGE types were, and similarly, significant differences in average
resistance to drying between groups of E. coli O157 with different ribotypes were seen. There were no differences between the abilities of isolates producing different Stxs (Stx 1 or Stx 1 and Stx
2) to survive drying. E. coli O157 isolates of PT4, PT21/28, and PT32 survived drying on concrete better than groups of other PTs did. Since the E. coli O157 isolates had various abilities
to survive drying on concrete, drying could contribute to a kind of E. coli O157 natural selection along the meat chain. This possibility may have significant meat safety implications if a range
of E. coli O157 isolates are simultaneously exposed to drying at any point along the meat production chain. Those E. coli O157 isolates that are more able to survive drying could be more likely
to pass farther along the meat chain and ultimately reach consumers.
Document Type: Research Article
Division of Food Animal Science, Department of Clinical Veterinary Science, University of Bristol, Bristol BS40 5DU, UK
Publication date: May 1, 2003
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