Incidence of Salmonella in Pennsylvania Egg Processing Plants and Destruction by High pH

Eggs and washwater samples from egg processing plants in southeastern Pennsylvania were examined for total bacterial counts and the incidence of Salmonella. Survey data indicated a greater number of microorganisms survived the washing process when low washing temperatures (32.2 to 35°C) and low pHs (pH 9 to 10) were used. Salmonellae belonging to group D₁ were found in washwater and on washed eggs from a plant which had washwater in this lower temperature and pH range. Plants that had washwater with high pH (pH 11.0 to 12.5) and high temperatures (37.7 to 43.3°C) had relatively low microbial counts in the washwater (7.5 × 10³ CFU/ml), and no salmonellae were detected in either washwater samples or on washed eggs. Both washwater pH and temperature had a dramatic effect on the survival of Salmonella enteritidis. At pH 11 and temperatures of 32.2°C (90°F), 37.7°C (l00°F) and 43.3°C (l10°F), S. enteritidis died rapidly, but at lower temperatures of 4.4°C (40°F) and 18.3°C (65°F) the death rate was much slower. At pH 9, S. enteritidis was able to grow slowly at 32.2 and 37.7°C; however, at 43.3°C, regardless of pH, S. enteritidis died rapidly. High detergent concentration and low egg solids concentration also increased the rate of destruction of S. enteritidis.