A study of the microbiological status of Irish farmhouse cheeses with emphasis on selected pathogenic and spoilage micro-organisms.

Ninety-six 25 g samples from 25 Irish farmhouse cheeses, two Irish non-farmhouse cheeses and four foreign cheeses were evaluated for the presence of a variety of micro-organisms, namely, coliforms, faecal streptococci, Staphylococcus aureus, yeasts, moulds, salmonellas and shigellas. Seventeen cheeses, i.e. the soft and semi-soft types, were examined for Listeria monocytogenes. Most of the farmhouse cheeses are currently manufactured from raw milk, but some producers now use heat-treated milk. The incidence of coliforms and faecal coliforms was higher in soft, semi-soft and semi-hard cheeses than in hard types. High levels of contamination by faecal streptococci and non-pathogenic (coagulase-negative) Staph. aureus prevailed in a high proportion of the cheeses. Pathogenic (coagulase-positive) staphylococci, however, were also isolated from 50% of the cheeses, some of which were manufactured from pasteurized milk. Yeasts were found mainly in unpasteurized varieties, especially in the category of soft cheeses. Moulds were isolated from five non-mould-ripened cheeses, as well as from mould-ripened varieties. Salmonellas, shigellas and Listeria monocytogenes were not detected after direct enrichment.