Enterobacteriaceae and related organisms recovered from retail shell eggs.

Authors: Musgrove, Michael; Jones, Deana

Submitted to: International Association for Food Protection Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/24/2007
Publication Date: 7/8/2007
Citation: Musgrove, M.T., Jones, D.R. 2007. Enterobacteriaceae and related organisms recovered from retail shell eggs.. International Association for Food Protection Proceedings.p.119.

Interpretive Summary:

Technical Abstract: Many types of shell eggs are available from retail markets. Some consumers believe that eggs from hens in alternative housing systems (cage free or free roaming) or from organically fed hens will be of superior microbiological quality. Little information is available on the genera of microorganisms that can be recovered from various retail shell eggs. A study was conducted to compare Enterobacteriaceae contamination of seven types of retail shell eggs. On three separate days, one dozen of the following eggs types were purchased locally and transported back to the laboratory: (A) traditionally fed, housed, and processed, (B) vegetarian fed/nutritionally enhanced, (C) in-shell pasteurized, (D) cage-free DHA enhanced, (E) cage-free, organic, fertile, (F) organic and free roaming, and (G) cage-free, organic, kosher. Eggs (10/type) were aseptically cracked, contents discarded, and the shells macerated with 10 ml phosphate buffered saline (PBS). Aliquots (1.0 ml) from individual eggs were duplicate plated using violet red bile glucose agar with overlay and incubated at 37oC overnight to detect Enterobacteriaceae. For each presumptive plate, 1-5 colonies were randomly selected and restreaked for purity. Purified isolates were then identified to genus or species using and automated biochemical testing system. There were 205 isolates identified. Enterobacteriaceae genera recovered included Cedecea, Citrobacter, Enterobacter, Escherichia, Klebsiella, Morganella, Pantoea, Proteus, Providencia, Salmonella, Serratia, and Yokenella. Closely related organisms identified from retail egg shells included Aeromonas, Burkholderia, Pseudomonas, Sphingobacterium, and Vibrio. Numbers of isolates identified per egg type were (A) 75, (B) 16, (C) 6, (D) 3, (E) 21, (F 42, and (G) 42. Salmonella were recovered from types A, B, and E. Traditional eggs (A) harbored the greatest number of isolates while in-shell pasteurized (C) and (D) cage-free nutritionally enhanced were the least contaminated. Bacterial contamination of shell eggs appears to be influenced by more than cage system or type of ration.