Growth and Survival of Campylobacter fetus subsp. jejuni as a Function of Temperature and pH

Abstract

The objective of this study was to determine what effect temperature and pH have on the ability of Campylobacter fetus subsp. jejuni to grow and survive. None of three strains of C. .fi·tus subsp.jejuni could grow at 30 C and below or at 47 C and above. The optimum temperature for growth was in the range of 42 to 45 C. Only one of three strains, FRI-CF8, could grow at pH 4.9 and none could grow at pH 4.7. The optimum pH for growth was in the range of 6.5 to 7.5; however, all strains grew well at pH 5.5 to 8.0. Rate of cell death at pH 3.0 to 4.5 was temperature-dependent. At comparable pH. cells of C. fetus subsp._jt:juni died most rapidly at 42 C, less rapidly at 25 C and at the slowest rate at 4 C. For example. at pH 4.5, a 3 log 10 decrease of cells occurred within 8 h when incubated at 42 C but took4 days when incubated at 4 C. At 25 C and pH 4.5, cells were inactivated at an intermediate rate. Rates of thermal inactivation of five strains of C. fetus subsp. jejuni were determined at 48, 50, 53. and 55 C in a skim milk heating menstruum. At 48 C. D-values ranged from 7.2 to 12.8 min while at 55 C they ranged from 0.74 to 1.00 min. The times and temperatures used to pasteurize milk should be sufficient to free milk of even unusually large numbers of viable cells of C. fetus subsp.jejuni. Campylobacter fetus subsp. jejuni has recently been recognized as a prominent cause of acute bacterial gastroenteritis in humans (3). Its rate of isolation is comparable to and in many studies exceeds the rate at which Salmonella is isolated from diarrheal stools of hospitalized patients. Both food and water have been implicated as vehicles responsible for transmitting campylobacters to susceptible individuals (1, 3. 5, 11-13, 21, 22). Foods derived from animals are of particular concern. Many species of animals, both wild and domestic, harbor C. fetus subsp. jejuni as part of their normal intestinal flora (17). Examples include poultry (4. 16), swine (10), cattle (17), sheep (15) and waterfowl (9). Since C. fetus subsp. jejuni may be present on meat (2, 5, 13, 18) or in milk (1. 7, 11, 12. 14, 21) obtained from such animals, it is important to know how these organisms will respond to conditions that may be present when foods are prepared and/or stored. Temperature and pH are two factors commonly employed by food processors to control or inactivate pathogens and undesirable microorganisms in foods. The purpose of this study was to determine what effect temperature and pH have on the ability of C. fetus subsp. jejuni to proliferate and/or survive in a medium supportive of its growth. Such information may be useful in identifying conditions and treatments that would render foods safe from the potential hazards of this prevalent pathogen. MATERIALS AND METHODS Organisms and cultural conditions All cultures of C. Jetus subsp.jejuni used for this study were isolated from human stool specimens and were obtained from A. Helstad (Wisconsin State Laboratory of Hygiene. Madison. WI). The cultures were identified as FR1-CFJ. FRI-CF6. FRI-CF8. FRI-CF12 and FRI-CF1b. In preparation for growth and survival studies. organisms were first cultured on blood agar plates containing Brucella agar (Difco) and 5% defibrinated sheep blood (Gibco). The plates were incubated for 3 days at 42 C in an atmosphere of 5'7o 0 2 :10% C0 2 :85% N 2 • Loopfuls of these cultures were transferred to 2 ml of Brucella broth (Gibco) containing 0.1 "i' o agar. Cultures were inoculated into the upper 1 em of the semisolid agar and were incubated at 42 C for 24 h. These cultures were subsequently transferred into 500-ml filter flasks, each containing 100 ml of Brucella broth supplemented with 0.3'7o sodium succinate (Mallinckrodt. Paris. KY) and 0.01% cysteine hydrochloride (Eastman, Rochester. NY). The atmosphere in the flasks was replaced with a gas mixture of 5% 0 2 :10% C0 2 :85% N 2 • then flasks were placed in a gyratory water bath (New Brunswick Scientific. New Brunswick, NJ, Model G 76) and shaken at 100 gyrations/min for 16 to 18 h at 42 C. Cells that were in the late logarithmic phase of growth were used as inocula for growth. survival and thermal inactivation studies. Gro\\'fh and sunivalstudies Studies were done in a series of screw-capped test tubes (16 mm x 125