Survival of Yersinia enterocolitica and mesophilic aerobic bacteria on eggshell after washing with hypochlorite and organic acid solutions

Populations of Yersinia enterocolitica O:9 and mesophilic aerobic bacteria on the shell of fresh chicken eggs were assessed prior and after washing with 0.75%, 1%, and 3% acetic and lactic acids, 50, 100, and 200 mg/liter (ppm) of chlorine, and water. Highest reductions of mesophilic aerobic bacterial populations (normal flora) on trypticase soy agar were 1.28 and 2.15 log(10) cycles with 100 and 200 mg/liter of chlorine, 0.28 and 0.36 log(10) cycles with 1% and 3% acetic acid, and 0.70 and 0.71 log(10) cycles with 1% and 3% lactic acid, respectively, as compared to the control group. No Salmonella or Yersinia were detected among the natural flora of the eggs. On Y. enterocolitica O:9-inoculated eggs, reductions of 2.66, 2.77, and 2.92 log(10) cycles by 50, 100, and 200 mg/liter of chlorine, of 2.47, 2.48, and 2.49 log(10) cycles by 0.75%, 1%, and 3% of acetic acid, and of 2.48 and 2.72 log(10) cycles with 1% and 3% of lactic acid, respectively, were observed with respect to the control. Organic acids at 3% caused detachment of the surface cuticle of the eggshell. Y. enterocolitica was more sensitive to the wash treatments than the natural microflora. The absence of potentially pathogenic Y. enterocolitica, observed for other fresh foods, should be a norm for fresh eggs sold in retail stores.