Risk Assessment Of Staphylococcus Aureus In Raw Milk

Staphylococcus aureus (S.aureus) widely spreads in nature, such as air, water, dust and human and animal excrement, etc. Milk, meat, eggs, fish and their products are mainly contaminated by S.aureus easily, which was the main cause of food poisoning pathogens in China. Enterotoxin produced by S.aureus can not be undermined by high-temperature sterilization, and can cause harm to human. S.aureus enterotoxin was a global health issue, which had drawn widely attention from countries around the world.Dairy farms and individual households milk in Harbin urban surrounding areas were researched in this paper, and the prevalence and levels of S.aureus in raw milk were surveyed. Meanwhile, the growth characteristics of this bacteria in raw milk was studied, and it was compared with that in sterilized milk. By fitting test datas with Gompertz equation, Richards equation and Logistic equation, the optimal growth model of S.aureus in raw milk was built with Predictive microbiology methods. Besides, with @RISK developed by Palisade Corporation, risk assessment report was completed by combining the epidemiological data with the survey of storage and transport conditions of raw milk in Harbin during acquisition process.The contents and results are as follows:The growth characteristics of the mixed S.aureus in raw milk was studied at 10℃, 13℃, 15℃, 17℃, 20℃, 26℃, 30℃and 37℃. The optimal growth model-Gompertz model and the secondary model were also built. The results showed that the growth of S.aureus can be predicted quickly and reliably by the model built; the positive rate of S.aureus in raw milk all reached 100%, average pollution level of positive samples was 2.16 log cfu/mL (retaining two significant figures); the storage and transport process of raw milk in Harbin urban surrounding areas was surveyed, the data of time and temperature of raw milk transported to dairy plant was also collected; in the risk assessment report, it was showed that exposure dose of raw milk cooled by cold water in individual milk households was the most serious risk, the mean level of exposure dose transported to dairy plant was 3.60 log cfu/mL(retaining two significant figures), above a threshold level of 105 cfu/mL in 7.08% and 106 cfu/mL in 0.5% respectively; the mean level of exposure dose transported to milk station and than to dairy plant was 3.61 log cfu/mL(retaining two significant figures), above a threshold level of 105 cfu/mL in 4.51% and 106 cfu/mL in 0.13% respectively; the mean level of exposure dose in dairy farm in summer was 3.59 log cfu/mL(retaining two significant figures), above a threshold level of 105 cfu/mL in 4.49% and 106 cfu/mL in 0.1% respectively, while in spring and autumn, the mean level was 3.45 log cfu/mL(retaining two significant figures), above a threshold level of 105 cfu/mL in 2.59% and 106 cfu/mL in 0.05% respectively; the probability of raw milk cooled by fridge and transported to milk station exceeded 105 cfu/mL and 106 cfu/mL was 0.79% and 0. Besides, the acquisition of other types of raw milk can not achieve the threshold dose of 105 cfu/mL, can not cause adverse health effects.