Construction Of Risk Monitoring And Exposure Assessment Model Of Staphylococcus Aureus During Pig Slaughtering

Staphylococcus aureus is one of the most important microorganisms causing food-borne diseases.Once humans consume food with S aureus and its enterotoxin,it will easily cause food poisoning,resulting in typical gastroenteritis symptoms such as vomiting and diarrhea.Currently,the contamination of S.aureus in livestock slaughter and processing is widespread which affects food safety and human health,but there are still deficiencies in the monitoring data and assessment methods of S.aureus in pig slaughterhouses in China and abroad.Therefore,this project conducted risk monitoring and disinfectant resistance tests on S.aureus in pig slaughterhouses in Hubei Province to investigate the current situation and transmission pattern of S.aureus contamination in pig slaughterhouses,and constructed exposure assessment models and growth prediction models based on the risk monitoring data to explore the key risk control points in pig slaughterhouses and to establish the safe storage time limits of raw pork at different temperatures.The main results are as follows:1.Staphylococcus aureus contamination and disinfectant resistance statusIn this study,a total of 880 samples were collected from a designated slaughterhouse in Hubei Province for isolation and identification,and the total isolation rate of S.aureus was 28.3%.Another 120 samples were collected for quantitative testing of S.aureus,and the concentration of bacteria in each link was 101 CFU/cm2～104 CFU/cm2.S.aureus was detected in all stages of the slaughterhouse,and the level of the bacteria was decreasing from scalding,baking and polishing,increasing from opening to splitting,and finally decreasing significantly from pre-cooling.Determination of minimum bactericidal concentration(MBCs)of sodium hypochlorite and benzalkonium bromide by micro-broth method.Evaluation of the sensitivity of slaughterhouse isolates to two disinfectants commonly used in slaughterhouses based on MBC results.The results showed that the MBC distribution of sodium hypochlorite on the isolates ranged from 2130 mg/L to 4260 mg/L,which was higher than the recommended use concentration(250 mg/L～2000 mg/L)in NY/T3075-2017;the MBC distribution of benzalkonium bromide on the isolates ranged from 11.875 mg/L to 47.5 mg/L,which was lower than the recommended use concentration in NY/T3075-2017(100 mg/L～5000 mg/L).2.Exposure assessment model for S.aureus in pig slaughterhousesA model for S.aureus exposure assessment in pig slaughterhouse was successfully constructed by@Risk software.The sensitivity analysis showed that the factors influencing the increase of S.aureus contamination level were:the number of bacteria carried by samples before scalding(correlation coefficient of 0.56),the rate of bacteria carried by samples before scalding(correlation coefficient of 0.34),and the amount of change in the opening session(correlation coefficient of 0.13).Combined with the significant reduction in the level of bacteria in the pre-cooling process,the risk control points of S.aureus in pig slaughterhouses were identified as the waiting,opening and pre-cooling processes.3.S.aureus growth prediction modelThe SGompertz model and quadratic polynomial equation were used to construct the growth prediction models of S.aureus at 10℃,16℃ and 25℃,and the fit R2 was greater than 0.99.The resulting time required for S.aureus to grow to 105 CFU/g(i.e.,the risk threshold)at an initial concentration of 103 CFU/g was calculated to be approximately 53 h,37 h and 8 h,respectively,which provides a reference for the development of shelf life for raw pork foods.