Listeria monocytogenes is ubiquitous bacteria. It causes listeriosis, a serious infectious disease which occurs as consequence of consumption of food contaminated with this pathogen bacterium. The frequency of incidence of listeriosis is low (1%), but with high mortality rate (30%). In certain countries (USA and Switzerland) large outbreaks of listeriosis were associated with consumption of fresh cheeses and milk. Studies on presence of L.monocytogenes in raw milk, carried out in Europe, have shown that 2,5-6% of samples can be contaminated with L.monocytogenes. In the process of production of milk and dairy products, it most commonly occurs as consequence of post-pasteurization contamination. L.monocytogenes has the ability to multiply and grow at low temperatures (4 0 C) and to survive even on freezing temperatures, and as such poses risk for health of consumers, if found in milk, cheese, ice-cream and other dairy products. In order to prevent the contamination of product with this bacterium, producers much implement prevention measures, and special attention must be focused on critical points in the production process and adequate sanitation. The general characteristics of L.monocytogenes, are presented in the study, also its resistance to environment, some listeriosis outbreaks, its presence in milk and dairy products and major hygiene measures.

Summary The aim of this study was to investigate aflatoxin M1 (AFM1) transfer from naturally contaminated raw milk into cheese and whey, during the production of Livanjski cheese (hard cheese type). Raw milk samples were collected from 4 farms in Serbia. The samples were then tested for AFM1 content and were later used for hard cheese production. Four cheese samples were produced, and the matching whey samples were also collected. The milk samples included two samples containing AFM1 above the EU maximum level (0.077±0.009 and 0.118±0.008 µg/kg) and the other two samples below the maximum level of 0.05 µg/kg (0.021±0.002 and 0.034±0.004 µg/kg). Regarding AFM1 transfer into cheese from the milk samples containing AFM1 above the EU maximum level, the rate was approximately 4-fold (383% and 410%). On the other hand, in the cheese samples made from milk containing AFM1 below the EU maximum level, almost 10-fold levels of AFM1 content in milk were found (transfer rates of 934% and 961%). As for the whey samples, AFM1 levels were below the levels found in the milk samples (transfer rates of 78%, 74%, 68% and 57%). The difference in the transfer rates for the cheese made from the milk samples contaminated at different levels may indicate the possibility that the AFM1 transfer rate from milk into cheese depends on the content of this toxin in milk.

The aim of this study was to determine the effect of selenium concentration in early lactation on mammary gland health and histological characteristics of the udder. The experiment included 30 high-yielding Holstein-Friesian cows. Selenium concentrations in blood and milk serum, and the average somatic cell count in the first and sixth months of lactation were analyzed. After exclusion of the experimental cows from the herd, histological characteristics of the udder were examined (the degree of leukocyte infiltration and the number of granulomas in the parenchyma). The mean selenium concentration in the blood serum was 0.62±0.11 mmol/L and that in the milk serum was 0.12±0.07 mmol/L. Optimal blood levels of selenium were found in 19 cows and suboptimal levels in 11 cows. A significant negative correlation was observed between blood and milk selenium concentrations and somatic cell count in early and mid lactation. There was no relationship between blood selenium concentration, milk selenium concentration and the amount of milk produced. Selenium-deficient cows had a significantly higher milk somatic cell count in early and mid lactation and significantly lower levels of selenium in milk. Upon histological analysis, 120 samples of individual quarters of the udder were grouped according to the degree of leukocyte infiltration and number of granulomas. Results showed that an increase in the degree of leukocyte infiltration and number of granulomas leads to an increase in the proportion of quarters from selenium-deficient cows and a decline in the percentage of quarters from cows exhibiting normal blood selenium concentrations. Selenium has a significant impact on udder health. Changes caused by selenium deficiency occur due to marked inflammation process in the mammary gland.

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