GROWTH AND PENETRATION OF SALMONELLA-ENTERITIDIS, SALMONELLA HEIDELBERG AND SALMONELLA-TYPHIMURIUM IN EGGS

Eggs and egg dishes are important vehicles for Salmonella infections. Salmonella enteritidis, Salmonella typhimurium and Salmonelia heidelbe rg, which can be isolated from chicken ovaries and feces, have been im plicated in approximately 50% of the foodborne salmonellosis outbreaks in the United States. In this study, the growth of these three organi sms, inoculated into yolks and albumen, was compared at 4, 10 and 25 d egrees C. Regardless of whether 10(2) cfu/g or 10(4) cfu/g was inocula ted into the yolk or albumen, populations of all strains increased 3 l ogs or more in number in one day when incubated at 25 degrees C. Maxim um numbers of Salmonella ranged from 10(8) to 10(10) cfu/g. All strain s grew at 10 degrees C, but peak numbers were lower and occurred later than those at 25 degrees C. Populations of the three Salmonella strai ns inoculated into eggs stored at 4 degrees C grew sporadically; in so me test groups populations declined. The potential for Salmonella in c ontaminated feces to establish in the interior of eggs was examined by monitoring shell penetration. At 25 degrees C, all three Salmonella s trains penetrated the shell in 3 days, but at 4 degrees C, only S. typ himurium was found in one membrane sample. When hatchery conditions we re simulated by incubating eggs at 35 degrees C for 30 min followed by storage at 4 degrees C, penetration was enhanced. Penetration was obs erved by day 1-3 when eggs were exposed to 10(4) cfu Salmonella/g fece s. Increasing the inoculum to 10(6) cfu/g feces resulted in 50-75% of the contents of eggs to be contaminated by day 1. All Salmonella-posit ive samples were detected by enrichment. Results of this study indicat e that S. enteritidis, S. typhimurium, or S. heidelberg present in fec es can penetrate to the interior of eggs and grow during storage.