Abstract: Objective To analyze the genetic characteristics of a food poisoning strain of Staphylococcus aureus (SA) in Shenzhen and understand the types of enterotoxins of SA, and to trace the source of the pathogenic bacteria causing by food poisoning. Methods Vomitus, anal swabs, suspicious foods, and environmental smear samples of the food poisoning were collected, and the strains were further isolated and biochemically identified. The enterotoxin genes were detected by fluorescence PCR, enterotoxins were detected by ELISA, and the isolated SA were tested by microbroth dilution. The whole genome sequencing method was used to sequence the strains, and the strain sequences were compared with the Resfinder, CARD, MLST, and VFDB databases to obtain drug resistance genes, ST types, and virulence factors, respectively. The phylogenetic tree was drawn by the bioinformatics analysis platform. Results SA was detected in 13 samples, with a positive rate of 65%, including 2 anal swabs from patients, 1 vomit sample, 5 food samples, and 5 environmental smear samples. A total of 36 strains of suspicious colonies were selected from the positive samples, none of them were detected with sea, seb, sec, sed, and see enterotoxin genes, 24 samples were detected by ELISA to produce type E enterotoxin, and the VFDB database results showed that 36 strains of SA carried the novel enterotoxin gene seg and enterotoxoid genes selm, seln, and selo. All strains were resistant to penicillin (100%) and sensitive to other antibiotics (0%). The strains carrying β-lactam resistance genes showed 100% phenotypic resistance, while the strains carrying tetracycline, quinolones, aminoglycosides, and other resistance genes did not show corresponding phenotypic resistance. All 36 strains were ST-1281 type, the SNP mutation site gap of the strains was small, and the SNP mutation site matrix ranging from 0 to 13. Conclusion This incident was caused by ST-1281 type SA, and it is a relatively rare food poisoning caused by a new type of enterotoxin.

Key words: Staphylococcus aureus, Enterotoxin, Whole genome sequencing, Microbroth dilution method, ST type