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 Salmonella heidelberg, which can be isolated from chicken ovaries and feces, have been implicated in approximately 50% of the foodborne salmonellosis outbreaks in the United States. In this study, the growth of these three organisms, inoculated into yolks and albumen, was compared at 4, 10 and 25 degrees C. Regardless of whether 10(2) cfu/g or 10(4) cfu/g was inoculated into the yolk or albumen, populations of all strains increased 3 logs or more in number in one day when incubated at 25 degrees C. Maximum numbers of Salmonella ranged from 10(8) to 10(10) cfu/g. All strains grew at 10 degrees C, but peak numbers were lower and occurred later than those at 25 degrees C. Populations of the three Salmonella strains inoculated into eggs stored at 4 degrees C grew sporadically; in some test groups populations declined. The potential for Salmonella in contaminated feces to establish in the interior of eggs was examined by monitoring shell penetration. At 25 degrees C, all three Salmonella strains penetrated the shell in 3 days, but at 4 degrees C, only S. typhimurium was found in one membrane sample. When hatchery conditions were simulated by incubating eggs at 35 degrees C for 30 min followed by storage at 4 degrees C, penetration was enhanced. Penetration was observed by day 1-3 when eggs were exposed to 10(4) cfu Salmonella/g feces. 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-positive samples were detected by enrichment. Results of this study indicate that S. enteritidis, S. typhimurium, or S. heidelberg present in feces can penetrate to the interior of eggs and grow during storage.