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United States Department of Agriculture

Agricultural Research Service

Title: Comparison of Sample Preparation Methods for Recovering Salmonella Enteritidis from Eggs

Authors
item Seo, Kun Ho
item Brackett, R - FOOD & DRUG ADMIN- MD
item Valentin-Bon, I - FOOD & DRUG ADMIN - MD
item Holt, Peter

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 23, 2003
Publication Date: September 1, 2003
Citation: Seo, K., Brackett, R.E., Valentin-Bon, I.E., Holt, P.S. 2003. Comparison of sample preparation methods for recovering salmonella enteritidis from eggs. International Journal of Food Microbiology.

Interpretive Summary: Human infections of Salmonella enteritidis (SE) caused by consumption of eggs contaminated with the organism remains a serious problem for the table egg industry. Flock and egg testing are important methods to combat this problem. Because of the low numbers of SE normally found in eggs, industry and regulatory agencies alike constantly search for new methods to improve detection of SE in egg contents. The current study examined the impact different procedures for processing egg contents prior to culture on recovery of SE. After 24 hours incubation, detection of SE was much lower in samples processed by mechanical means using either a stomacher or electric blender compared to manual methods such as hand massage or hand stirring. Processing the eggs with an electric blender gave the poorest results. Incubating the pools an additional 24 hours caused the SE to grow to equivalent levels in all four groups. In conclusion, the detection of low populations of SE in shell egg samples could be improved by using hand massaging and hand stirring methods for homogenization.

Technical Abstract: Homogenizing shell eggs for analysis of SE presence has been accomplished using a stomacher, an electric blender, and hand massage. However, to date, there have been no published reports that have described whether the method of homogenization affects recovery of SE from raw eggs. Three experiments were conducted using three different inoculum levels, 10, 126, and 256 SE cells/pool of ten eggs, respectively. The 10-egg pools were then homogenized by one of four different homogenization methods: mechanical stomaching, electric blending, hand massaging, and hand stirring for 30 s. The homogenized eggs were then incubated at 37C, and SE colonies were enumerated after 24 and 48 h incubation. After 24 h incubation, no SE was recovered from egg samples inoculated with less than 10 cells/pool and stomached or electrically blended while those samples which were whipped or hand massaged had levels of one million SE/ml. Similarly, recovery of SE from eggs containing 126 CFU/pool, homogenized by manual means (hand-massaging or hand stirring), and incubated for 24h was significantly greater than from eggs homogenized by mechanical means (stomaching or electric blender). The number of SE in samples treated with a blender was still statistically lower than the other three methods when the inoculum level was increased to 256 CFU/ pool SE. However, the number of SE in all samples approached to 9 log after 48 h incubation. In conclusion, the detection of low populations of SE in shell egg samples could be improved by using hand massaging and hand stirring methods for homogenization.

Last Modified: 8/29/2014
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