Staphylococcal food poisoning from sheep milk cheese

Area of Science:

• Food Safety and Microbiology
• Veterinary Public Health
• Dairy Science

Background:

• Food-poisoning incidents in December 1984 and January 1985 were linked to sheep milk cheese.
• Initial bacteriological examination of cheese did not identify viable pathogens.
• Staphylococcus aureus enterotoxin A was detected, marking the first such finding in UK-produced food linked to poisoning where the bacteria itself was not isolated.

Purpose of the Study:

• To investigate the source of Staphylococcus aureus contamination in sheep milk cheese implicated in food poisoning.
• To determine the persistence of Staphylococcus aureus and its enterotoxin production in dairy products and raw milk.
• To assess the role of animal health in dairy product safety.

Main Methods:

• Bacteriological examination of cheese batches.
• Detection of enterotoxin A.
• Detailed examination of milk, yoghurt, and cheese from the implicated producer.
• Investigation of Staphylococcus aureus contamination in sheep (ewes) including clinical and post-infection carriage assessment.

Main Results:

• Viable Staphylococcus aureus was not isolated from the implicated cheese, but enterotoxin A was present.
• Contamination of milk, yoghurt, and cheese was associated with Staphylococcus aureus in ewes, linked to both clinical illness and post-infection carriage.
• Enterotoxigenic Staphylococcus aureus strains were intermittently detected in bulk milk nearly two years later, even without apparent clinical illness in the sheep.

Conclusions:

• Post-infection carriage and subclinical shedding of Staphylococcus aureus by sheep can lead to enterotoxin contamination in dairy products.
• Heat treatment effectiveness requires consideration in controlling enterotoxin-producing bacteria.
• Current legislation regarding milk for human consumption should be expanded to include all non-human mammalian milk.