Multiplication in egg yolk and survival in egg albumen of genetically and phenotypically characterized salmonella enteritidis strains

Abstract

Prompt refrigeration of eggs to prevent the multiplication of Salmonella Enteritidis to high levels during storage is an important practice for reducing the risk of egg-transmitted human illness. The efficacy of egg refrigeration for achieving this goal depends on the interaction among the location of contamination, the ability of contaminant strains to survive or multiply, and the rate at which growth-restricting temperatures are attained. The present study assessed the significance of several characterized genetic and phenotypic properties for the capabilities of 10 Salmonella Enteritidis isolates to multiply rapidly in egg yolk and survive for several days in egg albumen during unrefrigerated (25°C) storage. The growth of small numbers of each Salmonella Enteritidis strain (approximately 101 CFU/mL) inoculated into egg yolk samples was determined after 6 and 24 h of incubation. The survival of larger numbers of Salmonella Enteritidis (approximately 105 CFU/mL) inoculated into albumen samples was determined at 24 and 96 h of incubation. In yolk, the inoculated Salmonella Enteritidis strains multiplied to mean levels of approximately 102.6 CFU/mL after 6 h of incubation and 108.3 CFU/mL after 24 h. In albumen, mean levels of approximately 104.6 CFU/mL Salmonella Enteritidis were maintained through 96 h. The concentrations of the various Salmonella strains after incubation in either yolk or albumen were distributed over relatively narrow ranges of values. Significant (P < 0.01) differences observed among individual strains suggested that maintenance of the fimbrial gene sefD may have positive genetic selection value by improving fitness to grow inside egg yolk, whereas the antibiotic resistance gene blaTEM-1 tet(A) appeared to have negative genetic selection value by decreasing fitness to survive in egg albumen.