Abundance of Vibrio populations in the gut of Japanese coastal fishes

Members of genus Vibrio, which are known as opportunistic pathogens of fish, often inhabit the gut of marine fishes. Polymerase chain reaction (PCR) primers specific to Vibrio spp. are required for rapid detection and quantification of opportunistic bacteria, which present a risk for infectious diseases. In this study, a primer set (VIB-F and VIB-R) was developed based on known probe sequences. The primer set amplified sequences from all strains of the genus Vibrio and related genera of the family Vibrionaceae, but not from strains of other families. In addition, clones in the library generated from marine fish gut using this primer set all corresponded to Vibrio spp. and other genera of Vibrionaceae, namely Aliivibrio, Enterovibrio, and Photobacterium. These results suggested that this primer set has sufficient specificity to permit estimation of the abundance of Vibrio spp. in the marine fish gut, facilitating the risk management of vibriosis. The quantitative PCR (qPCR) technique showed that the abundance of Vibrio spp. in the gut of coastal fishes was 1.1 × 105 – 9.9 × 1010 copies/g. These results revealed that the total count of bacteria in the gut of coastal fishes is relatively constant (ranging from 1.5 × 109 – 2.2 × 1011 cells/g), while the abundance of Vibrio spp. varies greatly. These results strongly suggest that the combination of Vibrio-specific primer set (VIB-F and VIB-R) and qPCR technique is a powerful tool for risk management against outbreaks of vibriosis in marine farms.