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

This study aimed at enumerating the viable number of various Vibrio spp., which cultured in tryptic soy broth with 3% NaCl (TSBN₃) or inoculated in mackerels, on thiosulphate‐citrate‐bile salts‐sugar (TCBS) agar and tryptic soy agar with 3% NaCl (TSAN₃), before and after storage at 4C for 3 or 7 days, depending on the use of seven diluents, including alkaline peptone water, phosphate buffered saline, artificial sea water with 2.5% NaCl (ASW₂.₅) or 0.75% NaCl (ASW₀.₇₅), deionized water with 3% NaCl (SSN₃) or 0.85% NaCl (SSN₀.₈₅) and TSBN₃. As a result, TSBN₃ was the most effective, showing by 5.25 log₁₀ cfu/mL on TCBS and 6.72 log₁₀ cfu/mL on TSAN₃ before storage. The highest numbers of Vibrio spp. were achieved when diluted in SSN₃ after storage for 3 days. Importantly, TCBS caused significant (P < 0.05) underestimations for enumerating the actual number of Vibrio spp. In addition, the use of ASW₂.₅ caused significant decreases in enumerating Vibrio parahaemolyticus and Vibrio vulnificus in mackerels (P < 0.05) after storage at 4C for 7 days. It was determined that enumerating Vibrio spp. could be influenced, depending on the use of diluents and a selective medium. PRACTICAL APPLICATIONS: Vibrio spp. with high pathogenicity may cause serious illnesses to human beings. Then, effective detecting methods have been required for analyzing the presence of Vibrio spp. from various seafood accurately/rapidly. However, it was revealed that concomitant results achieved after application of such methods would be different, depending on the use of diluents and a selective medium. These results would lead to the potential of not only a significant underestimation for enumerating the actual number of Vibrio spp., but also causing foodborne outbreaks associated with seafood. Therefore, the present study investigated effects of various diluents and a selective medium for enumerating Vibrio spp. in seafood. This research will provide scientific information that can be used for developing a program linked to effective detection of pathogenic bacteria in food.