engleski

Assessment of listeria monocytogenes in milk products, Zagreb area, Croatia

Listeria is a non-spore forming, rod-shaped bacterium ; nor encapsulated, with optimum growth temperature of 30-37 ºC. In the Listeria genus, only L. monocytogenes and Livanovii are associated with disease in humans Listeriosis can take three clinical forms: encephalitis, septicaernia and abortion, where mortality rate is giht. Listeria monocytogenes are ubiquitous bacteria and can be isolated from soil, vegetation, raw and processed foods. The number one way these bacteria can spread from the environment to people is via contaminated foods. Listeria monocytogenes presents a great hazard because of its ready propagation , which can already occur at 4 ºC (refrigerated temperature). Dairy products have been involved in several outbreaks. The incidence of L. monocytogenes in dairy products was investigated using the method described in ISO 10560 that includes several steps: first, homogenisation of 25g sample in 225 ml UVM (University of Vermont primary enrichment broth or half Fraser broth) and 24 hour incubation at 30 ºC, then 24-hour sub-cultivation of 0, 1 ml oft his pre-enrichment in 10 ml Fraser enrichment at 30 ºC. Next step is cultivation on selective agar (PALCAM or Oxford Listeria agar) at 37 ºC. After 24-48 hours, check if there are typical colonies. Listeria monocytogenes colony on Oxford agar was green-brown with a black halo, and the one on PALCAP agar was olive green to black. During the last three years (2002-2004), 250 sample of dairy products were investigated (20 pasteurized milk samples, 16 of dried milk, 24 of fermented milk products, 50 of fresh cheeses, 40 of hard and semi-hard cheeses and 100 samples of mould-ripened cheeses). Listeria monocytogenes was present in six samples (one semi-hard cheese and five mould-ripend cheeses). These obtained results tell us the state of dairy products in Croatia is good, bur also call for careful production methods, because in 2, 4% of these cases, the samples contained rare pathogens, for example L. monocytogenes.

Listeria monocytogenes; isolation

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