Isolation of Thermal Resistant Escherichia coli from Oyster and the Growth Protecting Effect of Pyruvate on Isolated Escherichia coli

Abstract

One hundred and ninety strains of Escherichia coli were detected in edible oysters collected from ten oyster beds in the Seto-Inland Sea . These strains were used for the investigation of thermal resistance and for the growth protective effect of sodium pyruvate against heat shock.
1. When the cells were heated in Heart Infusion Broth Medium at 50°C for 24hr, 74 of 190 isolates were heat resistant.
2. When these 74 strains were heated in Heart Infusion Broth Medium at 80°C for 1min, 39 isolates of these 74 strains were heat resistant.
3. Thirty-five strains, which were resistant at 50°C for 24hr heating but were not resistant 80°C for 1 min heating, were used to determine the growth protecting effect of 1% pyruvate against heat resistance at 80°C for 1 min in Heart Infusion Broth Medium. Twentyfour strains (69%) showed the growth protecting effect of 1% pyruvate against the heat resistance at 80°C for 1 min in Heart Infusion Broth Medium.