Shiga toxin-producing Escherichia coli in the milk production chain: Evaluation of virulence genes and clonal diversity of O157:H7 strains

Abstract

Microbial contamination of milk and dairy products is a significant issue due to sensory changes and the risk of foodborne diseases. Shiga toxin-producing Escherichia coli (STEC), particularly the O157:H7, are major pathogens transmitted by dairy products. This study aimed to evaluate the microbiological quality of bovine milk at various stages of the production chain in a dairy cooperative and its suppliers in Rio de Janeiro, Brazil. Additionally, the presence of STEC in milk and faeces from dairy cattle was investigated, along with the isolation of STEC O157:H7 strains and the evaluation of virulence genes and clonal diversity. These findings were compared with previously isolated STEC O157:H7 strains from the same region. A total of 100 raw milk samples (54 farm gallon (FG) samples, 25 community bulk tank milk (CBTM) samples, 14 isothermal car-tanker milk (ICTM) samples, and 7 industry tank milk (ITM) samples) and 10 pasteurized milk samples, along with 63 bovine faeces samples, were analysed. The stx gene, a marker for STEC, was detected in 65% of raw milk samples and 88.9% of faecal samples, indicating a high risk of contamination throughout the production chain. None of the pasteurized milk samples tested positive for the stx gene. The prevalence of stx in faeces and raw milk underscores the need for rigorous controls to prevent contamination. While pasteurization was effective, the microbiological quality of raw milk remained unsatisfactory, highlighting the importance of good hygiene practices and continuous monitoring to ensure dairy safety.