Optimization of ferrioxamine E concentration as effective supplementation for selective isolation of Salmonella enteritidis in egg white

Abstract

Utilization of ferrioxamine E (FE) as a sole source of iron distinguishes Salmonella from a number of related species, including Escherichia coli. FE 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 in egg white supplemented with FE. The optimum concentration of FE that promoted a selective advantage for Salmonella in egg white was determined. Four supplementation concentrations were evaluated (25, 50, 200, and 500 μg/ml) in egg white artificially inoculated with proportionally mixed cultures of a rifampin-resistant strain of Salmonella Enteritidis (0.1 ml of 102 CPU/ml) and E. coli K-12 (0.1 ml of 101 through 108 CPU/ml). After a 24-h incubation at 37°C, Salmonella and E. coli populations were enumerated. At higher concentrations of FE (>50 μg/ml), both Salmonella and E. coli were able to use the iron supplement (1 to 8.5 log CFU/ml and 1.8 to 8 log CFU/ml, respectively); however, lower FE concentrations (≤50 μg/ml) exclusively promoted Salmonella growth. Salmonella was unrecoverable without supplementation. This study indicates that optimum levels of FE supplementation in egg can improve the selective detection for Salmonella Enteritidis among other competitive organisms.