Use of Luminescent Strains of Salmonella enteritidis To Monitor Contamination and Survival in Eggs

Abstract

Fresh and retail eggs were exposed to luminescent S. enteritidis cultures containing from 104 to 109 CFU/ml at either room temperature (approximately 21°C) for 3 days or 40°C for 16 h. The entry of S. enteritidis through egg shell was evidenced by luminescence in the eggs which was visualized using an Image Quantifier. The rate of contamination of the eggs increased with increasing inoculum size. Scanning electron microscopy was used to confirm the position of S. enteritidis cells in the eggs. The survival rate of the Salmonella cells in liquid eggs and whole shell eggs during storage at 4°C was investigated. Although S. enteritidis did not grow in eggs during storage at 4°C for up to 8 weeks, cells were able to survive. Under these storage conditions, the count was reduced by 1.7 to 2.5 log cycles per g in liquid egg and 0.8 to 1.4 log cycle per g in whole shell eggs. Similar trends were observed using both plate count and luminescence to monitor survival.