GROWTH OF Vibro parahaemolyticus AT LOW SALT LEVELS AND IN NONMARINE FOODS

Two strains of V. parahaemolyticus were studied with respect to salt requirements in Nutrient Broth, effects of freezing and heat stresses on salt requirements, and growth in nonmarine foods. Nutrient Broth containing 0.0235M Na plus K ions was supplemented with NaCl, KCl, Na 2 SO 4 and K 2 SO 4 in concentrations from 0.0342M–0.5132M. V. parahaemolyticus did not grow without supplementation. Both strains grew at a mimimum total NaCl concentration of 0.0855M (0.5%) and maintained viability at 0.0513M (0.3%) NaCl. Strain 17802 could utilize KCl, Na 2 SO 4 and K 2 SO 4 as alternate ion sources and gave essentially the same growth patterns as with equimolar concentrations of cation from NaCl. Strain 27519 required slightly higher concentrations of KC1 and Na 2 SO 4 than strain 17802 but did not grow at any level of K 2 SO 4 supplementation. NaCl requirements in Nutrient Broth were only very slightly changed by stresses of frozen storage at −18°C up to 30 days and were esentially unchanged by heating at 50°C for 15 min. Both strains grew profusely in beef, turkey, pudding, milk and egg at 37°C and 25°C, reaching levels within 12 hr, in most cases, sufficient to cause food poisoning by pathogenic strains. To a more moderate degree growth also occurred at 9°C, reaching viable counts of 10 5 /ml in 12 hr in all of these foods except egg. At 9°C none of the foods exhibited visual or odor changes indicative of spoilage even after 72 hr, while at the higher temperatures such signs of spoilage were absent in several cases where counts exceeded 10 7 −10 8 /ml. Green beans of pH 4.95 did not support growth or maintain viability of either strain. The levels of NaCl in the Nutrient Broth and foods that supported growth of V. parahaemolyticus in these studies were lower than generally reported in the literature.