Sapovirus (SaV) is an important pathogen causing gastroenteritis in humans. Studies of SaV outbreak associated with food-handlers who were infected with SaV have been frequently reported. However, the precise reports about the duration of SaV shedding from food-handlers are not found in SaV food-borne outbreak. In this report, we examined quantitative analysis of the viral loads in 36 stool specimens from 10 food-handlers (5 symptomatic food-handlers and 5 asymptomatic food-handlers), and genetic analysis of the detected viruses were performed. Our results showed that SaV excretion decreased to an undetectable level on 44 days; however, some individuals excrete SaV in feces at high concentrations until 33rd days after outbreak. In addition, we identified the amino acid substitutions caused by the point mutation at the capsid region on 21st days. We should carefully monitor the food-handlers excreting SaV to prevent the spread of food poisoning associated with SaV.

View full abstract

One hundred and seventy-five strains of enterohemorrhagic Escherichia coli (EHEC) O157, expressing stx1 and stx2 genes, were isolated from 464 stool specimens collected from patients of foodbone outbreak associated with consumption of Japanese dumpling (dango and kashiwamochi) occurred in Yamagata city, Japan. We found that two strains of them formed white colonies on selective and differential agar, CHROMagar O157. CHROMagar O157 has been expected to contain at least three substrates, X-α-galactoside, X-β-glucoside and X-β-glucuronide, which is utilized to detect α-galactosidase, β-glucosidase and β-glucuronidase, respectively. Many enterobacteriaceae species including non-0157 E. coli, form blue colonies on CHROM agar O157 as the result of hydrolysing the substrates by β-glucosidase and β-glucuronidase, whereas EHEC O157 has been supposed not to form blue colonies but mauve colonies because of its α-galactosidase activity instead of the lack of both β-glucosidase and β-glucuronidase. As expected, the fermentation tests of EHEC O157 (stx1+stx2) having white aspect on CHROMagar O157 showed negative results for the activities ofα-galactosidase, β-glucosidase and β-glucuronidase. The result of PCR, however, showed that they have both of melA and melB genes. Therefore, it has been suggested that EHEC O157 (stx1+stx2) forming white colonies on CHROM agar O157 has the mutations in melA and melB genes, resulting in the suppression of α-galactosidase.

View full abstract