Pathogenic analysis on a foodborne disease outbreak caused by Salmonella Enteritidis in Wuhan, 2021

  Objective  To identify the cause of a foodborne disease outbreak in Wuhan in 2021.

  Methods  The pathogen was isolated and cultured from the food samples, cases’ anal swabs and stool samples in this foodborne disease. VITEK 2 Compact automatic microbial identification system was used for the identification of isolated strains, and serological typing test and drug resistance sensitivity test were carried for these strains. The nucleic acid of the pathogenic bacteria and the strains with same type isolated sporadically in this area in the past two years were extracted for pulsed field gel electrophoresis (PFGE) and whole genome sequencing, and the virulence genes and drug resistance genes of the strains were analyzed by gene annotation and sequence alignment, combined with multi-locus sequence typing. Phylogenetic tree was constructed based on single nucleotide polymorphism, and homology analysis was performed to trace the origin of pathogenic bacteria.

  Results  A total of 5 strains of Salmonella Enteritidis were isolated, of which 2 were from food samples and 3 were from anal swabs of the cases. The 5 strains had same PFGE pattern and showed resistantance to amikacin, gentamicin, tobramycin, cefazolin, cefoxitin, sulfamethoxazole and cefuroxime. The isolated strains belong to ST11 type, carrying same resistance genes and virulence factors. Only one mutation site was detected in the sequences of the strains isolated in this outbreak. The whole genome sequence of the strains in this outbreak was highly similar to the sequences of the S. Enteritidis strains isolated from local cases.

  Conclusion  This foodborne disease outbreak in Wuhan was caused by S. Enteritidis circulating in this area. Whole genome sequencing can be used as a supplement to pulsed field gel electrophoresis for epidemiological investigation of disease outbreak.