Quantification of Thermostable Direct Hemolysin-Producing Vibrio Parahaemolyticus from Foods Assumed to Cause Food Poisoning Using the LightCycler Instrument

Abstract

Vibrio parahaemolyticus isolated from the feces of patients with food poisoning contains in most cases either thermostable direct hemolysin (TDH) and/or TDHrelated hemolysin (TRH), both important pathogenic factors carried by this microorganism [1–3]. However, most organisms from brackish water, estuary mud or fish that cause food poisoning have neither the TDH production gene (tdh) nor the TRH production gene (trh) [1]. This seems to be because TDH-producing V. parahaemolyticus occurs in only small amounts in nature or foods compared to other Vibrio spp. In addition, it is difficult to grow in artificial media, since TDH-producing V. parahaemolyticus is in the viable but nonculturable (VNC) state due to nutrient limitation, low temperature, etc. [4, 5]. Therefore, TDH-producing V parahaemolyticus is rarely isolated from foods assumed to cause food poisoning that have a high probability of containing TDH-producing V. parahaemolyticus Accordingly, it is very difficult to quantitate TDH-producing V. parahaemolyticus by culture. In order to estimate the content of TDH-producing V. parahaemolyticus in suspect foods, we have developed a LightCycler assay to quantitate tdh.