Laboratory studies of growth conditions of Vibrio parahaemolyticus in Pacific oyster (Crassostrea gigas) with international considerations to shellfish-associated illnesses in South Korea

Vibrio parahaemolyticus, a naturally occurring halophilic pathogen, is seasonally abundant in marine and estuarine environments. It is also the leading cause of gastroenteritis in humans world-wide. Numerous outbreak incidences associated with the pathogenic Vibrio parahaemolyticus contaminations in oyster products have raised public-health concerns as well as economic challenges to the shellfish growers since the discovery of the bacteria in 1950s. A lack of molecular understanding in association of the bacteria and the host animal, C. gigas, has been conducted in the Häse lab which aims to find bacterial factors in the host animal interaction and “targeted intervention strategies” to remove the presence of the pathogen. A preliminary study for the in vitro assay was initially designed to help the molecular study. It tested bacterial adherence to animal samples in different temperature and salinity levels with a single-factor scheme. The average number of inoculates for each temperature and salinity treatment were 1.65 x 108 ± 5.39 x 107 CFU/ml and 2.11 x 108 ± 2.05 x 107 CFU/ml with the mean animal’s gut weight of 6.61 ± 0.09g and 6.69 ± 0.23g respectively. From the temperature treatments, the average number of V. parahaemolyticus isolates per gram sample was 4.47 x 105 ± 3.23 x 105 CFU/ml. From the three different salinity level treatments (1%, 3%, and 6% NaCl), the average number of the bacterial isolates per gram sample was 1.84 x 105 ± 2.62 x 105 CFU/ml. The result from the study had shown that the\ud 3\ud optimal growth condition for V. parahaemolyticus was at 37˚C and 3% NaCl. Better bacterial adherence occurred in temperature treatment groups of V. parahaemolyticus compared to E. coli. Better bacterial adherence occurred in treatment groups of room temperature (21.5˚C) and the concentration of 6% NaCl. Yet, high resource variables in the research design and low precisions seemed to create higher margin of errors and limited understanding for the optimal bacterial growth conditions associated with the degree of bacterial adherence to the animal. The research recommends greater sample numbers and replicates in order to reduce the high variability associated with bacterial growth for the future related assay developments