Fate of Indigenous Verocytotoxin-Producing Escherichia coli in Uncooked, Raw Milk Cheeses

Introduction:  Verocytotoxin-producing Escherichia coli (VTEC) is a foodborne pathogen that can cause severe illness and death. Cattle is a natural reservoir of VTEC; consequently, they may be isolated from raw cow milk and non-pasteurized dairy products, like Uncooked Raw Milk Cheeses (URMC), typically produced in many Italian regions.

Purpose:   The aim of this study was to assess a survey of VTEC in URMC, produced in the Northern Italy, and to study the fate of indigenous VTEC during seasoning.

Methods:  From 2013 to 2016, a total of 1,029 curd samples of URMC were analyzed to check for the presence of VTEC using the standard method, ISO/TS 13136:2012. Cheeses produced with positive curds were collected and the fate of the pathogen was studied.

Results:  VTEC were detected in 28 out of 1,029 curd samples (2.72%, with 1.82% - 3.91% Confidence Interval at 95% significance level). The proportion of positive samples decreased during cheese ripening. After 8 months at 14°C, the water activity (a_w) decreased to between 0.977 and 0.919 and no VTEC was detected in the samples.

Significance: These data confirm that the cheese ecosystem, especially a_w, affects VTEC survival. This study can help safety authorities improve the risk analysis of URMC.