Effect of Storage Temperature on the Survival of New Zealand Egg-Associated Isolates in and on Eggs.

The influence of egg storage temperature on contamination of eggs is a key consideration in determining storage and shelf life recommendations for eggs. In this study, experiments assessed the survival of isolates on and in eggs at storage temperatures (15 and 22°C) currently used in New Zealand. Eggshell surfaces were inoculated with a cocktail of 10 isolates comprising five serotypes, at a concentration of ∼10 CFU per egg (for determining shell surface survival) or ∼10 CFU per egg (for determining internalization). Additionally, a subset of eggs was artificially contaminated with sterile chicken feces prior to inoculation. Inoculated eggs were incubated at 15 and 22°C. At 0, 21, and 35 days of incubation, eggshells were enumerated for and egg contents were tested for presence or absence (yolk) or most probable number (albumen). Higher levels of were recovered from eggshells following incubation at 15°C (31% relative humidity [RH]) compared with 22°C (45% RH) after both 21 and 35 days of incubation. Recoverable numbers of from visibly clean eggshell surfaces declined over time at both storage temperatures and were at, or below, the limit of detection from eggs stored at 22°C and 45% RH for 35 days. A substantially higher concentration of viable was recovered from eggshells that were experimentally contaminated with chicken feces compared with those without, particularly from eggs stored at 15°C and 31% RH for 35 days (2.38 log higher CFU from eggs containing feces). No was detected in egg contents (albumen or yolk) at any incubation temperature or time point, regardless of the presence of feces. Findings emphasize the importance of current regulations that require eggs sold at retail to be visibly clean and will inform risk management decisions regarding egg storage times and temperatures with respect to control in and on New Zealand eggs at retail.