Detection of Escherichia albertii in retail oysters.

Escherichia albertii  is an emerging foodborne pathogen. Owing to its distribution in river water,  it is important to determine the presence of  E. albertii  in aquaculture-related foods. In this study, we investigated the distribution of  E. albertii  in retail oyster samples.  A total of  427 raw oyster samples (385 Pacific oysters, and 42 Japanese rock oysters) were enriched in  modified Escherichia coli  broth (mEC) or mEC supplemented with novobiocin (NmEC) at 42 °C. The cultures were used for  E. albertii -specific nested PCR assay, as well as for  E. albertii  isolation using  deoxycholate hydrogen sulfide lactose agar  (DHL), DHL supplemented with rhamnose and xylose (RX-DHL), and MacConkey agar supplemented with rhamnose and xylose (RX-MAC). The population of  E. albertii  in nested PCR-positive samples was  determined using the  most probable number  (MPN) method.  E. albertii  isolates were subjected to biochemical and genetic characterization.  E. albertii   was detected in 5 of 315 (1.6%) Pacific oyster samples  (one piece each), 2 of 70 (2.9 %)  Pacific oyster samples  (25 g each), and 2 of 42 (4.8 %) Japanese rock oyster samples  procured from four geographically distant regions. A total of 64  E. albertii  strains were isolated from eight of the nine nested PCR assay-positive oyster samples, and  the MPN value was under the detection limit (< 3 MPN/10 g).  A specific season or month for detecting  E. albertii  was not observed in this study, suggesting that the pathogen is present in seawater.   All the  E. albertii  isolates, except one, were positive for the virulence factor  eae,  indicating that these isolates have  the potential to infect humans.