Repression of Vibrio parahaemolyticus by Pseudomonas species isolated from processed oysters

45 cultures isolated from processed Maryland oysters stored at 5{degree}C were examined for inhibitory activities against various strains of V.parahaemolyticus by a spot-plate method. 9 oyster islates which demonstrated inhibitory activity were identified as Pseudomonas sp. Inhibition was more pronounced at 25{degree}C than at 35{degree}C and increased with decreasing levels of V.parahaemolyticus. Type and composition of plating medium, including pH, salt and peptone content were important factors. Inhibition was maximal at 0.5% NaCl and decreased with increasing salt concs until little or no inhibition was observed at 2.5% NaCl. Effect of pH was variable according to strain of V.parahaemolyticus used. Addition of trypticase or phytone to tryptone-glucoseyeast extract agar decreased inhibition to different degrees. Pigmentation of Pseudomonas cultures was strong when production of inhibition was maximal. In general, pathogenic strains of V.parahaemolyticus tested were inhibited to a lesser degree than were nonpathogenic strains.