Survival of Bacteria at a Subfreezing Temperature (－1°C)

Preservation of foodstuffs at temperatures around ?1°C has attracted special interest recently. We investigated whether bacteria contaminating foodstuffs, especially contaminating fish, were killed or survived at ?1°C compared with 37°C. Survival rates of Escherichia coli K12 and Staphylococcus aureus IFO12732 in nutrient broth at ?1°C for 7 days were 52% and 31%, respectively. However, the survival rate of Vibrio parahaemolyticus in nutrient broth containing 3% NaCl at ?1°C for 7days was only 0.03%. When the bacteria were kept in a soy sauce solution containing alcohol and some seasonings (the soy sauce solution) at ?1°C, survival rates of E. coli K12 and S. aureus IFO12732 after 2 days were 56% and 54%, respectively, but V. parahaemolyticus was completely killed after 24 h at ?1°C in the soy sauce solution. When E. coli K12 and O157 and V. parahaemolyticus were incubated at ?1°C in the soy sauce solution containing some pieces of raw fish (the improved soy sauce solution), 3 strains of the bacteria were not killed. These results indicate that bacteria contaminating fish are not killed at ?1°C and that storage of fish at ?1°C is not always effective in diminishing food poisoning.