Enterotoxin Gene Profiles And Genotypes Of Food-borne Staphylococcus Aureus Isolates From Shanghai

In this study, food samples were collected from super-markets and terminal markets in Shanghai, and Staphylococcus aureus was isolated and identified according to GB4789.10-2010. In addition, PCR was performed for further confirmation of these isolates, and their enterotoxin genotype diversity analysis and Multilocus Sequence Typing (MLST) were carried out.Firstly, Staphylococcus aureus was isolated and identified from 505 food samples (including raw milk, raw meat, fruits,vegetables, aquatic products, frozen food and soy products) according to GB4789.10-2010. Staphylococcus aureus was found in 117 food samples, and 183 strains of Staphylococcus aureus were isolated with a total detection rate of 23.2%. There are remarkable differences among different kinds of foods. Raw meat had the highest detection rate of 32.9%; followed by frozen food (26.7%) and raw milk (26.3%); the detection rate of fruits and vegetables, aquatic products and soy products was lower than 16.0%. The results have basically reflected the distribution of Staphylococcus aureus in some types of food from Shanghai, which might provide clues for monitoring Staphylococcus aureus in food processing, controlling food-poisoning and tracing of pollution sources.Secondly, the main reason of food poisoning caused by Staphylococcus aureus is its enterotoxins, so PCR was performed to detect the distribution of enterotoxin genes among the Staphylococcus aureus isolates. Among the 183 isolates, 161 strains were positive for enterotoxin genes, with the total carrying rate of 88.0%. There was no enterotoxin genes found in 22 isolates, accounted for 12.0%. Seb and sem had the highest detection rate(48.1%); see was not found; the carrying rate of 5 traditional enterotoxin genes ( including sea,seb,sec,sed,see) is lower than that of the newly found enterotoxin genes; 28 strains contained virulence gene cluster called egc, which contained seg,sei,sem,sen and seo(or seu) at the same time, with the carrying rate of 15.3%. There were 141 isolates contained 2 or more kinds of enterotoxin genes, accounted for 77.0%, and 9 isolates contained more than 10 kinds of enterotoxin genes, accounted for 4.9%.Finally, in order to identify the correlation and characteristics of Staphylococcus aureus isolates, MLST was applied for the gene typing. A total of 22 STs were found among the 183 isolates. ST-188 had the largest number of 101 isolates; followed by ST-2094 and ST-7, respectively 22 and 20 strains; ST-97, ST-5, ST-1281, ST-398 and ST-1 were also very common. Besides, the STs varied among different kinds of foods. The main ST of fresh meat was ST-7(19 isolates); followed by ST-188(7 isolates). ST-188 was the main ST of raw milk with 67 isolates;followed by ST-2094(15 isolates). Among fruits and vegetables and frozen food isolates, ST-188 is the main ST. ST-15,ST-5,ST-512,ST-188 and ST-2094 appeared in bean products.