Distribution of Escherichia albertii in Retail Shellfish in Akita Prefecture, Japan, and Characterization of the Isolates

Abstract

Escherichia albertii is a newly emerging foodborne pathogen causing diarrhea, and its distribution in environmental water and various animals as birds and raccoons has been reported. However, the infection routes of E. albertii to humans remain unclear. In this study, we aimed to determine the distribution of E. albertii particularly in shellfish. In 112 samples examined, a total of eight E. albertii strains were isolated from seven samples of retail shellfish, including three samples of Japanese basket clam called Shijimi in Japan, two samples of Japanese rock oyster, and two samples of pacific oyster. These isolates possessed major biochemical properties and sufficient tolerance of salinity equivalent to seawater. In these isolates, eae, paa, and Eacdt as virulence gene were detected, similarly to human-derived E. albertii strains. Additionally, Eccdt-I and stx2f were also detected only in one isolate from Japanese rock oyster. Furthermore, a certain E. albertii strain was highly susceptible to cefixime using as selective agent in enrichment broth and other beta-lactams, indicating that two-step enrichment method using two kinds of selective enrichment broth is an efficient approach for isolating various E. albertii strains. Pulsed-field gel electrophoresis analysis revealed that one of E. albertii isolates from shellfish exhibited a high degree of genetic similarity to E. albertii strains from human and environmental water. Our results suggest that shellfish can be a source of infection for humans through the transmission of E. albertii from other sources, such as contaminated environmental water.