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[Listeria monocytogenes in pasteurized milk]
Abstract:
An haemolytic Listeria monocytogenes strain pathogenic to mice was isolated from 6 out of 28 (21.4%) pasteurized milk samples (3.2% fat milk treated at 78 degrees C for 15 s) marketed by a Madrid processing plant. Listeria grayi was recovered from 25 of the samples (89.2%) and L. innocua from 3 samples (10.7%). One milk sample was contaminated with L. welshimeri. No strains of L. ivanovii, L. seeligeri, L. murrayi, or L. denitrificans were isolated. These results show that pathogenic Listeria strains can be isolated from pasteurized milk and reinforce the hypothesis that this food product may be the source of numerous human listeriosis.
Insights
Pathogenic Listeria monocytogenes strains were found in 21.4% of pasteurized milk samples in Madrid. This highlights pasteurized milk as a potential source of human listeriosis outbreaks.
Area of Science:
- Food microbiology
- Bacteriology
- Public health
Context:
- Pasteurized milk is a widely consumed product.
- Listeria monocytogenes is a significant foodborne pathogen.
- Previous studies have indicated potential contamination of dairy products.
Purpose:
- To investigate the prevalence of Listeria species, including pathogenic strains, in pasteurized milk from a Madrid processing plant.
- To assess the risk of Listeria contamination in pasteurized milk.
Summary:
- A study isolated an haemolytic Listeria monocytogenes strain pathogenic to mice from 6 out of 28 (21.4%) pasteurized milk samples.
- Listeria grayi was the most frequently detected species (89.2%), followed by L. innocua (10.7%).
- Other Listeria species, including L. welshimeri, were also identified, but L. ivanovii, L. seeligeri, L. murrayi, and L. denitrificans were not found.
Impact:
- Demonstrates that pathogenic Listeria strains can survive pasteurization and be present in milk.
- Reinforces the hypothesis that pasteurized milk is a potential vehicle for human listeriosis transmission.
- Underscores the importance of stringent quality control in milk processing to ensure food safety.