Staphylococcus aureus and Escherichia coli prevalence in ovine bulk tank milk

Occurrence of Listeria monocytogenes and Escherichia coli in Raw Sheep's Milk from Farm Bulk Tanks in Central Italy

ABSTRACT

For milk hygiene and safety, the milking phase is a critical moment because it is a probable pathway for the introduction of unwanted microorganisms in the dairy chain. In particular, Listeria monocytogenes and Escherichia coli are known as possible microbial contaminants of raw sheep's milk, although extensive knowledge regarding their contamination dynamics on sheep farms is still lacking. This study aimed to examine the occurrence and concentration of these microorganisms in milk samples collected from farm bulk tanks in the region of Lazio (Central Italy) and to investigate the related risk factors. Over a period of 1 year, we collected 372 milk samples from 87 sheep farms and administered a questionnaire to acquire information regarding relevant farm management variables. L. monocytogenes was not found in any of the samples, which indicates a low occurrence of this pathogen in sheep's bulk tank milk. In contrast, E. coli was found in almost two-thirds of milk samples (61%) but at levels below 102 CFU/mL in most of them (approximately 75%). Statistical analysis indicated that, during the warmest seasons, E. coli presence is more probable and counts are significantly higher. Unexpectedly, milk collected by hand milking had a lower level of contamination. Although further studies are necessary to clarify some aspects, the reported data add to the knowledge about the occurrence of L. monocytogenes and E. coli in raw sheep's milk and will be useful for future risk assessments.

HIGHLIGHTS

A large meta-analysis of the global prevalence rates of S. aureus and MRSA contamination of milk

Past reports have indicated a high prevalence of milk contaminated with Staphylococcus aureus (S. aureus) and methicillin-resistant Staphylococcus aureus (MRSA), but the pooled prevalence rates of S. aureus and MRSA in pasteurized and boiled cow's milk, raw cow's milk, and raw Caprinae milk (raw sheep's milk and raw goat's milk) and across different periods, continents, economic conditions and purchase locations remain inconsistent. We searched relevant articles published in PubMed, EMBASE, and Web of Science before July 2016. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement was used to evaluate the quality of 93 included studies. We observed that the pooled prevalence rates of S. aureus contamination in pasteurized and boiled cow's milk, raw cow's milk, and raw Caprinae milk were 15.4% (95% CI, 6.1-27.5%), 33.5% (95% CI, 29.5-37.7%) and 25.8% (95% CI, 17.5-35.0%), respectively. The pooled prevalence rates of MRSA contamination were 4.9% (95% CI, 0.0-15.7%), 2.3% (95% CI, 1.3-3.6%), and 1.1% (95% CI, 0.5-1.8%), respectively. The prevalence of S. aureus contamination in raw cow's milk increased over time. However, the pooled prevalence of raw cow's milk contaminated with S. aureus was lowest in European studies. These findings give an indication of the consequence of better milk regulation in Europe. High S. aureus prevalence rates in raw milk collected from farms and processing companies pose a potential threat to consumers. The implementation of good hygiene practices, appropriate health knowledge, and food safety principles at the farm level, as well as the prudent use of antibiotics in veterinary medicine and heat treatment before drinking, are necessary to reduce the potential risk of S. aureus and MRSA contamination.