A foodborne outbreak caused by atypical enteropathogenic Escherichia coli O45:H15 in the Kinki region of Japan.

Atypical enteropathogenic Escherichia coli (aEPEC) mainly causes sporadic diarrhea and occasional outbreaks. However, the genetic determinant of aEPEC causing large outbreaks is still unknown. In June 2022, 171 of 934 people presented with diarrhea and abdominal pain after eating a lunch box in the Kinki region of Japan. We investigated 44 fecal samples from persons who ate the cuisine and isolated enteropathogenic Escherichia coli (EPEC) serotype O45:H15 from 38 of them. The same pathogen was also isolated from the feces of two employees and a leftover sample (mashed tofu salad with spinach). Pulsed-field gel electrophoresis and whole genome sequencing supported the clonality of the isolates. The isolates were negative for bfpA, encoding the bundle-forming pilus, and were accordingly identified as aEPEC. Whole genome sequencing revealed the presence of a plasmid-encoded type 3 secretion system effector gene, espT, involving the invasive phenotype of EPEC. Finally, we concluded that this was a foodborne outbreak caused by aEPEC O45:H15. Since the food poisoning case caused by aEPEC O45:H15 harboring espT has not been reported previously, the current study broadens our understanding of aEPEC food poisoning and its genetic background.IMPORTANCEaEPEC causes diarrhea in humans, despite the reported asymptomatic carriers of aEPEC worldwide. Several outbreaks caused by aEPEC also support that this pathogen is a diarrheagenic agent; however, the genetic determinant of aEPEC causing large outbreaks is still unclear. In 2022, a large foodborne outbreak by aEPEC O45:H15 affected more than 170 people in the Kinki region of Japan. We sequenced the whole genomes of the etiological agents and identified a potential virulent plasmid carrying espT, which is a virulence factor of aEPEC O111 that caused diarrhea in more than 600 people in Finland. Our data strengthen the importance of espT as a virulence factor of aEPEC outbreaks.