Optimization of iron supplementation for enhanced detection of Salmonella Enteritidis in eggs

Mixed raw egg contents were inoculated with approximately 10 CFU of Salmone lla Enteritidis and supplemented with 0 to 7 mg of FeSO4 per g of egg conte nts. Egg contents were then incubated at 37 degreesC. and Salmonella Enteri tidis colonies were enumerated for up to 106 h. Iron supplementation signif icantly enhanced the growth of Salmonella Enteritidis. Within the first 24 h of incubation, the optimum iron level for Salmonella Enteritidis growth i n egg contents was between 0.2 and 2 mg of FeSO4 per g of egg contents. Aft er 24 h of incubation at 37 degrees C. Salmonella Enteritidis counts in egg s supplemented with 0.5 mg of FeSO4 per g of egg contents consistently reac hed approximately 1 x 10(9) CFU/ml, whereas Salmonella Enteritidis counts i n eggs without iron supplementation varied from less than 5 CFU/ml to 8.4 x 10(6) CFU/ml. A 3 by 3 factorial design was used to study the effect of ty pe of preenrichment and level of iron supplementation on the growth of Salm onella Enteritidis in egg contents. No significant differences in Salmonell a Enteritidis counts between preenrichment and nonpreenrichment treatments were observed when egg contents were supplemented with 0.5 mg of FeSO4 per g of egg contents. It was concluded that preenrichment was not necessary fo r isolation of Salmonella Enteritidis from eggs. The effect of iron supplem entation on the sensitivity of detection by the direct plating method was i nvestigated. The direct plating method detected a significantly higher perc entage of Salmonella Enteritidis in raw egg contents supplemented with 0.5 mg of FeSO4 per g of egg contents (90%) than in raw egg contents without ir on supplementation (63.3%).