Effect of Temperature and pH on the Survival of Campylobacter fetus ¹

Test strains of C. fetus subsp. jejuni and C. fetus subsp. intestinalis failed to survive heating in skimmilk at 60 C for 1 min. A few strains survived heating in skimmilk at 55 C for 1-3 min. D_50C values for C. fetus subsp. jejuni and C. fetus subsp. intestinalis in skimmilk ranged from 1.3-4.5 and from 1.0-3.7, respectively. No survivors of C. fetus subsp. jejuni and C. fetus subsp. intestinalis were detected in beef roasts inoculated at levels of 10⁶-10⁷ viable cells per g when the final temperature in the center was 57 and 55 C, respectively. At an internal temperature of 50-53 C, survivors of C. fetus were detected in beef roasts. Storage of skimmilk, beef and ground beef inoculated with C. fetus at -20, 1, 10, 20, 30 or 40 C resulted in decreases in C. fetus count. Survival of C. fetus was best at 1 and 10 C. Rapid increases in C. fetus counts occurred at 37 C in Brucella broth adjusted to pH 6-8. At pH 5, no survivors were detected after 24 h. At pH 9, counts of C. fetus subsp. jejuni decreased rapidly while those of C. fetus subsp. intestinalis increased slightly.