Ecology and seasonal distribution of Vibrio parahaemolyticus in aquatic environments of a temperate region

Physiological characterization of aerobic culturable bacteria in the intestine of the sea cucumber Apostichopus japonicus

Various aerobic culturable bacteria (1,133 isolates) were isolated from the gut of Apostichopus japonicus (black adult, green adult, black small, green small, black juvenile, and green juvenile sea cucumbers) and from the sea sediment and the seawater using different culture conditions and without enrichment culture. By molecular analysis of partial 16S rRNA gene sequences of 231 isolates, they were tentatively affiliated with 53 described species in the phyla Firmicutes (42 species), Proteobacteria (9 species) and Actinobacteria (2 species). Eighteen species were often found among the intestines and the sea sediment. High diversity was observed in the genus Bacillus (20 species), Oceanobacillus and Virgibaillus but there were no isolates affiliated to members of the genus Vibrio, well-known sea pathogens. There were no clear differences in the bacterial communities among the hosts varied in size and color. Most isolates showed various polysaccharide degradation activities, suggesting their possible contributions in the digestion of organic matters in the gut.

Ecological study of pathogenic vibrios in aquatic environments

An ecological study of pathogenic vibrios in aquatic environments of Okayama was carried out. The number of Vibrio parahaemolyticus detected in the sea area was comparatively smaler than that found in the survey of about two decades ago. Various reasons for the decrease in the case of food poisoning by V. parahaemolyticus have been suggested but the lower number of the vibrio in aquatic environments may be one explanation. Although the number of V. vulnificus was also not as large, most of the isolates possessed the pathogenic genes, vvp and vvh, suggesting the potential for fatal pathogenicity to patients having underlying diseases. As for V. cholerae, some non-O1/non-O139 serovar isolates were detected in a fresh water area, and many of them had hlyA, the gene for hemolysin which acts as a pathogenic factor in sporadic cases of diarrhea. Thus, the total number of pathogenic vibrios detected was not of concern. However, the marine products of these areas are shipped in wide area and are for general consumption. Therefore, it is necessary to continue to survey pathogenic vibrios in aquatic environments in order to ensure food hygiene.