Preliminary attempts towards production of table eggs free from Salmonella enteritidis

Abstract

The aim of this preliminary work is to reach to a cleaner production of intact shell-table eggs free from Salmonella enteritidis (SE) contamination, by application of pasteurization and dry heat. Three highly virulent strains of SE, previously reported to the World Animal Health Organization, were used in this study. The three strains acquired plasmid profiles similar to SE isolates reported in severe food illness of humans. The plasmid profiles of the three SE strains were: strain 1 (14.1 kb), strain 2 (14.1 and ≈50.0 kb), and strain 3 (1.8, 14.1, and ≈50.0 kb). Each of the three SE strains grown up to 10 h (stationary phase) and adjusted to the same light transmission of 12% at a wavelength of 540 nm, was homogenized with yolk of eggs to form three individual inocula. Strain 1 inoculum to eggs resulted in initial SE count/ml of egg content equivalent to 1.80×10 19 colony forming unit (cfu); however, strain 2 inoculum resulted in 2.3×10 19 cfu, and strain 3 inoculum resulted in 2.20×10 19 cfu ( P>0.05). Treatment of inoculated intact shell eggs in a hot water bath at 57°C for 25 min, followed by application of hot air at 55°C for another 57 min resulted in the highest reduction in SE count/ml of the egg content for strain 1 (average 33.33 cfu), followed by strain 2 (average of 0.73×10 4 cfu), and strain 3 (average of 1.60×10 4 cfu). All counts after treatment were significantly less than the initial count before treatment ( P<0.05). Decreasing the density of the SE in the three inocula by about 13 logs to be 1.80×10 6 cfu/ml of egg content for strain 1, 2.34×10 6 for strain 2, and 2.20×10 6 for strain 3 ( P>0.05) and applying the same pasteurization and dry heat treatment on inoculated eggs resulted in complete absence of viability in the three strains, averaging zero cfu/ml of egg content. The pasteurization and dry heat treatment of intact shell-table eggs results in significant reduction of the high initial count of SE strains, regardless of their plasmid profile or density of contamination. The production of table eggs completely clean of SE could be obtained by the same treatment when the initial contamination is low (around 10 6 cfu/ml of egg content).