<i>Escherichia coli</i> O-genotyping PCR and H-genotypingPCR Methods on Food Poisoning of Diarrheagenic <i>E. coli</i>

Diarrheagenic Escherichia coli strains are mainly classified into the following five pathotypes; enteropathogenic E. coli, enterotoxigenic E. coli, enteroinvasive E. coli, enterohemorrhagic E. coli and enteroaggregative E. coli. E. coli strains of various pathotypes can be further classified by their serotypes combined by O-serogroup and H-type. Generally in Japan, the commercial O-antisera and H-antisera are used to serotype strains. These serotypes provide useful information in investigations of outbreaks and epidemiological studies. In May 2021, a large-scale food poisoning outbreak thought to be caused by E. coli occurred in Saitama City. Serotyping of 21 E. coli strains carrying virulence genes isolated from patients and an asymptomatic cooking worker was carried out using a commercially available kit, but most of the strains (57%) could not be serotyped. Therefore, in this study, we tried the multiplex PCR methods including E. coli O-genotyping PCR and E. coli H-genotyping PCR. As a result, only 5% of strains could not be determined their Og-types, and the main genotype in this case was found to be Og104:Hg4 (12/21 strains) carrying astA+aggR or estA2+elt+astA+aggR. In conclusion, we believe that Og-typing PCR and Hg-typing PCR are effective methods in investigating cases caused by pathogenic E. coli belonging to rare pathotypes.