Microbial risk assessment of Escherichia coli shiga-toxin producers (STEC) in raw sheep's milk cheeses in Italy

Abstract

Shiga toxin-producing E. coli (STEC), widespread pathogens associated with severe foodborne disease, can contaminate milk during the milking process through faecal matter and survive or grow during cheese making if a pasteurization treatment has not been applied. Thus, a stochastic “farm-to-fork” model was developed to assess the risk of human infection by O157 STEC, one of the main pathogenic serotypes, associated with the consumption of a portion of raw sheep's milk cheese produced in a farmhouse dairy in Italy. The average risk of illness after the consumption of a portion of brief-, medium- and long-ripened cheese ranged between 1.64 × 10−4 and 4.03 × 10−4 for adults. Considering only a difference in serving size, the risk for children varied from 1.35 × 10−4 to 3.34 × 10−4. Among the several intervention strategies simulated to mitigate the risk, administration of bacteriophages was, by far, the most effective measure with an average risk reduction of 34 times followed by use of probiotics and antimicrobials, which lowered the risk about 12 times. The sensitivity analysis showed that the probability that a shedder is present in the herd, the occurrence of the milk contamination with faeces and the within-herd prevalence of the pathogen were the parameters that most affected the risk. While further data is necessary to confirm the conclusion of this study, the model results might be able to assist producers and policymakers to manage the risk of STEC infection linked to such products.