Evaluation of Diluents and A Selective Agar for Enumerating the Viable Number of Vibrio Spp. in Laboratory Broth and on Mackerel

Development of enhanced selective media for detection of Vibrio parahaemolyticus in oysters

This study was undertaken to develop enhanced selective media for detection of Vibrio parahaemolyticus in oysters. Primarily, tryptic soy agar (TSA) was supplemented with 4.5-5% NaCl, 0.1-0.5% oxgall, and/or 1-2% sodium citrate, and adjusted to pH 8-9. A total of 21 Vibrio spp., 24 indicators, and 26 food-borne isolates were streaked on the modified media, followed by 24 h of incubation at 37 °C. While all the indicators and isolates failed to grow on TSA containing 5% NaCl, 0.5% oxgall, and 2% sodium citrate (TSA_OSS1; pH 9), V. parahaemolyticus was culturable on this selective medium. Particularly, the ability of TSA_OSS1 to quantify V. parahaemolyticus in oysters was superior to thiosulphate citrate bile salts sucrose (TCBS) agar. V. parahaemolyticus distinctly produced its white-yellowish, round, and edge-pointed colony on TSA_OSS1. TSAO_SS1 with high selectivity potentials over TCBS may be a promising alternative for detection of V. parahaemolyticus in seafoods or natural reservoirs.

Supplementary Information

The online version contains supplementary material available at (10.1007/s10068-021-00877-0).

Effects of varying concentrations of sodium chloride and acidic conditions on the behavior of Vibrio parahaemolyticus and Vibrio vulnificus cold-starved in artificial sea water microcosms

There has been limited information available on the behavior of Vibrio parahaemolyticus and Vibrio vulnificus as a function of higher levels of NaCl in combination with acidic pH. In the present study, bacterial suspensions were transferred into artificial seawater (pH 4-7) microcosms containing 0.75% NaCl and supplemented with 5, 10, and 30% NaCl, respectively. Each of V. parahaemolyticus and V. vulnificus was inoculated in these microcosms and fermented seafood, and then stored at 4 °C until the microbial populations reached below the detectable levels on agar plates (thiosulphate-citrate-bile salts-sucrose agar and tryptic soy agar amended with 3% NaCl). Consequently, V. parahaemolyticus ATCC 27969, V. parahaemolyticus ATCC 33844, and V. vulnificus ATCC 33815 rapidly reached the viable-but-nonculturable (VBNC) state with increasing levels (≤30%) of NaCl at 4 °C. Within seven days, these pathogens in seafood appeared to enter the VBNC state at 4 °C, as shown by the fluorescence microscopic assay.