Effect of Temperature, pH, and Detergent on Survival of Bacteria Associated with Shell Eggs

Survival was studied of shell egg related microorganisms that were subjected to various combinations of water temperature, pH, and the presence of egg-washing detergents. Numbers of Salmonella typbimurium in buffered tryptic soy broth (BTSB) increased over a 7-hr period at pH 7 and 8 in water temperatures 35, 40, and 45 C. At pH 9 and 45 C, counts gradually decreased. At pH 10 and 11 counts always decreased, sometimes to 0, regardless of temperature. At 50 and 55 C, counts always decreased, sometimes to 0, regardless of pH. In commercial egg washing detergent (pH 11) at 50 C, survival of Salmonella, Citrobacter, Enterobacter, Proteus, and Klebsiella strains ranged from 0 to 90 seconds during several replicates. Survival times of most were extended somewhat in the presence of 1.0% suspended whole egg solids (e.g., Klebsiella—3 min). Strains of Alcaligenes, Flavobacterium, and Pseudomonas demonstrated survival trends similar to those of the enterics: Flavobacterium survived the longest, almost 4 min either with or without egg material in the detergent solution. Pseudomonas and Escherichia coli were killed off almost instantaneously under the same conditions. Survival of Staphylococcus aureus was adversely affected by the presence of the detergent (12 min) but was somewhat protected by the egg material (37 min). Streptococcus faecalis was virtually unaffected in either case, surviving up to 2.5 hr.