The majority of raw milk cheese in England is of good microbiological quality, according to a recent report on a study.

A total of 629 samples of cheese were collected from retailers, catering sites, and manufacturers in England between April 2019 and March 2020. Almost 12 percent were unsatisfactory.

The majority were made using cow’s milk, with 86 made from sheep’s milk and 31 from goat’s milk. Samples were from 18 different countries with most from the United Kingdom or France.

Using European unio microbiological criteria and UK guidance, 82 percent, or more than 500 samples, were of satisfactory quality, 34 samples were borderline, and 74 were unsatisfactory.

Four samples contained potentially harmful levels of bacteria but no evidence for associated human infection was found. High levels of coagulase-positive staphylococci was detected in two samples and Listeria monocytogenes and Shiga toxin-producing E. coli (STEC) in one each.

Regulation and sampling issues
Indicator E. coli and Listeria species were detected more often in soft cheese than hard. Higher levels of indicator E. coli were associated with a greater likelihood of detecting Shiga toxin genes. These genes were detected in 10 samples.

The study, published in the Journal of Food Protection, aimed to gather data on the prevalence of pathogens and bacterial indicators of poor hygiene in unpasteurized, raw milk cheese to inform future risk assessments.

EU regulation does not have criteria for E. coli in raw milk cheese. UK rules advise that ready-to-eat food sampled at the point of sale is of borderline quality if the E. coli count was greater than 20 CFU/g and unsatisfactory if above 100 CFU/g. The Specialist Cheesemakers’ Association suggests a target of below 100 CFU/g E. coli for hard cheese and below 10,000 CFU/g for soft or semisoft cheese.

There are technical challenges with detecting STEC in food and the significance of finding stx genes by PCR in the absence of an associated cultured stx-positive E. coli isolate is not yet fully understood, said researchers.

STEC O181:H49 was isolated from a hard cow’s milk cheese collected from retail with an indicator E. coli level of under 20 colony forming units per gram (CFU/g).

Type of milk and storage impact
Listeria monocytogenes was present at a potentially hazardous level of above 100 CFU/g in one sample of a hard goat’s cheese. It was detected at below 100 CFU/g twice: a blue cow’s milk cheese and a blue sheep’s milk cheese. Other Listeria species were found in 18 of 584 samples, of which five had levels above 100 CFU/g.

Coagulase-positive staphylococci were detected at more than 20 CFU/g in seven of 629 samples but none had levels above the upper limit in EU legislation.

The proportion of samples made from sheep’s milk with unsatisfactory results was lower than for cheeses made from cow’s milk and occurrence of E. coli levels above 20 CFU/g was significantly lower in sheep’s milk cheeses than cow’s milk.

Unsatisfactory results and the presence of stx genes were detected in cheeses from the UK more frequently than those originating from other countries but more UK samples were cow’s milk cheeses, which could partly explain this finding, said researchers.

More than 500 samples were stored at 0 to 8 degrees C (32 to 46.4 degrees F) at the time of sampling, while 70 were stored above this temperature. Those at 0 to 8 degrees C had significantly fewer unsatisfactory results compared with those above 8 degrees C. The increase in non-compliant results when stored at higher temperatures was greater for soft and blue cheeses compared with hard cheeses.