Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/7/2005
Publication Date: 3/1/2006
Citation: Thammasuvimol, G., Seo, K.H., Song, K.Y., Holt, P.S., Brackett, R.E. 2006. Optimization of ferrioxamine e concentration as effective supplementation for selective isolation of salmonella enteritidis in egg white. Journal of Food Protection.69(3):634-8. Interpretive Summary: Interpretive Summary: Salmonella Enteritidis remains a serious foodborne illness problem. Screening potentially infected layer flocks for production of eggs contaminated with this organism is an important component of many quality assurance programs in the U.S. To enhance recovery of S. Enteritidis from egg contents, iron compounds are added which aid in growth of the organism in this iron-poor environment. However, most iron compounds also support growth of competing organisms that can cause problems in S. Enteritidis detection. Ferrioxamine E (FE) is an iron compound that can be utilized by Salmonella but not by contaminating intestinal organisms such as Escherichia coli and Proteus. A study was conducted to determine how well FE enhances S. Enteritidis growth compared with E. coli in egg contents. In the presence of high concentrations of FE (> 50 'g/ml), growth of S. Enteritidis and E. coli in egg contents were comparably enhanced while at levels less than 50 'g/ml, enhancement of growth was observed for only S. Enteritidis. These results indicate that FE, when used at optimal levels, would be superior to other iron supplements for increasing the recovery of S. Enteritidis from egg contents.
Technical Abstract: Technical Abstract: Utilization of ferrioxamine E (FE) as a sole source of iron distinguishes Salmonellae from a number of related species, including Escherichia coli (E. coli). Ferrioxamine E is not able to serve as a source of iron for E. coli or the Proteus-Providencia-Morganella group. This confers a selective advantage on Salmonella Enteritidis (SE) in egg white supplemented with FE. The optimum concentration of FE for selective advantage for Salmonella in egg white was determined. Four supplementation concentrations were evaluated (500 'g/ml, 200 'g/ml, 50 'g/ml, and 25 'g/ml) in egg white artificially inoculated with proportionally mixed cultures of a rifampicin-resistant strain of Salmonella Enteritidis (0.1 ml of 102 CFU/ml) and E. coli K12 (0.1 ml of 101 through 108 CFU/ml). After 24 h incubation at 37'C, Salmonella and E. coli populations were enumerated. At higher concentrations of FE (> 50 'g/ml), both Salmonella and E.coli were able to utilize the iron supplement (log 1 – 8.5 and log 1.8 – 8 CFU/ml, respectively), however lower FE concentrations (' 50 'g/ml) exclusively promoted Salmonella growth. Salmonella was unrecoverable without supplementation. This study indicates that optimum levels of FE supplementation in egg can improve selective detection for Salmonella Enteritidis among other competitive organisms.