Survival of Listeria monocytogenes in wilted and additive-treated grass silage.

Grass was field-dried to 3 different dry matter (DM) levels (200, 430 and 540 g/kg) and inoculated with 10(6)-10(7) cfu/g of a Listeria monocytogenes strain sharing a phagovar occasionally involved in foodborne outbreaks of listeriosis. Formic acid (3 ml/kg) or lactic acid bacteria (8 x 10(5)/g) with cellulolytic enzymes were applied only to forages with low and intermediate DM levels. Forages were ensiled in laboratory silos (1700 ml) and were stored at 25 degrees C for 30 or 90 days. After 90 days of storage, L. monocytogenes could not be detected in any silo, except one with the high dry matter grass without additive. After 30 days of storage, between 10(2) and 10(6) cfu L. monocytogenes/g silage were isolated from the untreated silages. Increasing the DM content from 200 to 540 g/kg did not reduce listeria counts possibly because of the lower production of fermentation acids (higher pH). In silages treated with additives, counts of L. monocytogenes were always lower than in silages without additive. In wet silages (DM 200 g/kg) both additives were effective, but in the wilted silages (DM 430 g/kg) only the bacterial additive reduced listeria counts below detection level. Listeria counts were highly correlated to silage pH (r = 0.92), the concentration of lactic acid (r = -0.80) and the pooled amount of undissociated acids (r = -0.83).

Bacteriological quality of on-farm manufactured goat cheese.

The bacteriological quality of 198 ripened soft or semi-soft goat cheeses obtained from dairy farms and the retail trade was investigated. The cheeses were examined for total counts of aerobic bacteria, coliform bacteria (37 and 44 degrees C respectively), enterococci, coagulase positive staphylococci, Bacillus cereus and Clostridium perfringens. Cheeses obtained from dairy-farms were also determined for pH value. In terms of all tests performed, cheeses made of heat-treated milk with starter culture had the best prospects for fulfilling the criteria for 'fit for consumption'. Cheeses made of raw milk without starter culture made up the most unsatisfactory group from a food-hygiene point of view. Bacteriological guidelines for on-farm manufactured goat cheese are suggested.