Objective To efficiently produce Clostridium perfringens alpha toxin(CPA)by using a prokaryotic expression system and systematically analyze its biological activity.Methods The CPA gene fragment fused with His-Tag sequence was cloned into a prokaryotic expression vector pTIG-Trx and transformed into E.coli TransB(DE3).The IPTG was used to induce the expression of the target protein,and the protein was obtained by using Ni-column affinity purification.The cytotoxic effect of recombinant CPA protein on 293T,LS174T and SW480 cells,hemolytic effect on human and mouse red blood cells,and lethal effect on mice were further evaluated.Results The recombinant CPA protein with a relative molecular weight of about 45×103 and a purity of more than 90％was successfully obtained.It had significant toxicity to 293T,LS174T and SW480 cells and induced hemolytic reactions in human and mouse red blood cells at specific concentrations.Low dose of CPA protein could cause rapid death in mice in a short time.Conclusion This study successfully obtained the high purity CPA protein with good biological activity in vitro and in vivo,which laid a foundation for further study of the pathogenic mechanism of CPA and its potential application.

Objective　In order to find out the cause of the clustered epidemic events in 2 districts of Chengdu, quickly control the development of the incident and prevent the recurrence of such incidents. Methods　From July 2020 to October 2021, three clusters of epidemics with fever and sore throat as the main manifestations occurred successively in two districts of Chengdu City. Through the investigation of all relevant personnel in industrial parks and schools, case investigation and epidemiological analysis were carried out to establish the etiological hypothesis. Retrospective cohort study and case-control were used to carry out the epidemiological investigation. The investigation of food safety and environmental hygiene was carried out through interviews, data reference, field investigation and other ways to further find out possible harmful links and risk factors. Respiratory tract and intestinal biological samples and environmental samples were collected for rapid screening, bacterial culture and PCR detection of common respiratory tract and intestinal pathogens.Results　The three incidents identified 65 cases (21.5% prevalence), 158 cases (29.2% prevalence) and 93 cases (1.0% prevalence), respectively. The clinical manifestations were mainly fever, sore throat, and malaise, with occasional abdominal pain, diarrhea, nausea, vomiting, and rash. The epidemiologic curves suggested a point-source exposure pattern, with no spatial aggregation and no specific populations affected. Analytical epidemiological investigations suggested that some of the food items in the cafeteria may have been risk factors within three days before the onset of illness. Food hygiene investigations revealed that, prior to the onset of the incidents, coleslaw was provided without a proper cold dish processing area in all three events. Approximately a week before the onset of Incident B, a cafeteria food handler sustained a hand injury but was not reassigned. Streptococcus dysgalactiae was detected in throat swabs of multiple cases in all 3 incidents, and the same strain was detected in cafeteria workers in Incident B. Conclusions　All three incidents were foodborne disease outbreaks caused by Streptococcus dysgalactiae contamination. Likely contributing factors include contamination of animal food raw materials, food handlers continuing to work while infected, and non-standard preparation of cold dishes in canteens. It is suggested that the future foodborne disease risk should be highly concerned about the fever aggregation outbreak caused by Streptococcus dysgalactiae.