Influence of freezing temperature on survival of Eseherichia coli O1S7:H7

The effect of freezing temperatures (-18 and -75 degree C) on two strains (ES1 and ES2) of Eseherichia coli O157:H7 was evaluated. The strains were inoculated in beef broth samples to simulate meat contamination, and a rich (Tryp-ticase Soy Agar) and selective medium (Violet Red Bile Agar) was used to estimate the extreme limit of growth and recovery after a stocking period of 60 days. Both strains of E. coli O157:H7 studied were able to survive freezing treatments. Cell viability was significantly af-fected by -18 degree C, but only marginally by -75 degree C. Strain ES2 demonstrated a better adaptation to freezing stress than strain ES1, confirming that this can be strain-specific.