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Incidence of pathogenic bacteria in raw milk in Ireland
Abstract:
Raw milk from 70 farms was sampled over 13 months for salmonellas, listerias, Escherichia coli, Staphylococcus aureus and mastitic streptococci; total bacterial counts (TBC), coliforms and somatic cells were also counted. TBC < or = 30,000/ml were obtained in 63% of samples. High count milks were found mainly during the winter months: 13% of samples had > 10(4) mastitis pathogens/ml of milk. The mean somatic cell count varied from 4.0 x 10(5) to 8.0 x 10(5)/ml throughout the year with highest counts during the late lactation period. Coliforms were present in all samples, but 65-71% of samples had < 100 coliforms/ml. Up to 60% of supplies had < or = 10 E. coli/ml. One of the 589 samples tested (0.1%) was positive for salmonellas. Yersinia enterocolitica and Y. enterocolitica-like organisms were isolated from 39% of samples with up to 68% of samples positive at some sampling periods. A total of 222 strains of yersinias were isolated; Y. enterocolitica (59%) was the most common strain followed by Y. fredriksenii (35%), Y. kristensenii (1.0%), Y. intermedia (4.5%) and Y. aldovae (0.5%). Listerias were isolated from 8.3% of samples tested; 4.9% were Listeria monocytogenes and 3.4% were L. innocua. There was a significant rise in the isolation rate between December and April from a base line of 0-5% during the spring and summer to 35-37% during the winter months while the cows were indoors. Of 66 silage samples tested from the farms involved in the survey 9% of samples were positive for listerias; 3% of these were L. monocytogenes and 6% were L. innocua.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
This study analyzed raw milk quality from 70 farms over 13 months, finding Listeria prevalence increased significantly in winter. While most samples had low total bacterial counts, winter months showed higher pathogen levels, especially from cows housed indoors.
Area of Science:
- Food Microbiology
- Dairy Science
- Public Health
Background:
- Raw milk consumption carries potential health risks due to microbial contamination.
- Understanding the prevalence and seasonality of specific pathogens in raw milk is crucial for food safety assessments.
Purpose of the Study:
- To assess the microbiological quality of raw milk from multiple farms over a year.
- To identify seasonal variations in the occurrence of key bacteria, including pathogens like Listeria and Yersinia.
Main Methods:
- Collected raw milk samples from 70 farms over 13 months.
- Quantified total bacterial counts, coliforms, somatic cells, and specific pathogens (Salmonella, Listeria, E. coli, S. aureus, mastitic streptococci).
- Analyzed silage samples for Listeria contamination.
Main Results:
- Most samples (63%) had total bacterial counts <= 30,000/ml; higher counts were noted in winter.
- Listeria spp. isolation increased significantly from 0-5% (spring/summer) to 35-37% (winter), particularly when cows were housed indoors.
- Yersinia enterocolitica was found in 39% of samples; Salmonella was rare (0.1%).
- Silage samples showed Listeria contamination (9%), with L. monocytogenes in 3%.
Conclusions:
- Raw milk microbiological quality exhibits seasonal fluctuations, with increased Listeria risk during winter months when cows are indoors.
- Silage can be a source of Listeria contamination in dairy farms.
- Ongoing monitoring of raw milk and farm hygiene practices is essential to mitigate risks.