Multiplication in egg yolk and survival in egg albumen of genetically and phenotypically characterized Salmonella Enteritidis strains

Authors: Gast, Richard; Guard, Jean; Guraya, Rupinder - Rupa; LOCATELLI, AUDE - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2018
Publication Date: 6/1/2018
Citation: Gast, R.K., Guard, J.Y., Guraya, R., Locatelli, A. 2018. Multiplication in egg yolk and survival in egg albumen of genetically and phenotypically characterized Salmonella Enteritidis strains. Journal of Food Protection. 81:876-880.

Interpretive Summary: Refrigerating eggs promptly after they are laid is an important practice for reducing the risk of transmitting Salmonella Enteritidis infection to consumers of contaminated eggs. Refrigeration helps prevent small bacterial numbers from multiplying to more dangerous levels, especially when contaminants are present inside nutrient-rich egg yolks. This study compared the abilities of ten Salmonella Enteritidis strains to grow rapidly in egg yolk and to survive for several days in egg albumen during storage at 25 C. Each of these strains had been previously characterized for several significant genetic and cellular characteristics. After inoculation of egg yolks with very small numbers of cells of each strain, Salmonella Enteritidis multiplication reached mean levels that were more than 10 million times greater by 24 h of incubation. Alternatively, after inoculation of egg albumen samples with much larger cell numbers of each strain, Salmonella Enteritidis levels remained nearly constant through 96 h of incubation. Relatively little overall variation between strains was observed in Salmonella concentrations after incubation in either yolk or albumen. However, significant differences that were detected between individual strains suggested that possessing a gene that coded for fimbrial protein structures on the bacterial cell surface may have been useful for growth inside egg yolk, whereas maintaining a gene that coded for antibiotic resistance may have reduced bacterial survival in egg albumen.

Technical 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 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 ten Salmonella Enteritidis isolates to multiply rapidly in egg yolk and survive for several days in egg albumen during storage at 25 C. The growth of very small numbers of each Salmonella Enteritidis strain (approximately 10e1 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 10e5 CFU/ml) inoculated into albumen samples was determined at 24 h and 96 h of incubation. In yolk, the inoculated Salmonella Enteritidis strains multiplied to mean levels of approximately 10e2.6 CFU/ml after 6 h of incubation and 10e8.3 CFU/ml after 24 h. In albumen, mean levels of approximately 10e4.6 CFU/ml of Salmonella Enteritidis were maintained through 96 h. Relatively little variation between strains was observed, as Salmonella concentrations after incubation in either yolk or albumen were distributed over relatively narrow ranges of values. Significant (P < 0.01) differences observed between individual strains suggested that maintenance of the fimbrial gene sefD may have positive genetic selection value for growth inside egg yolk, whereas the antibiotic resistance gene blaTEM-1 tet(A) appeared to have negative genetic selection value for survival in egg albumen.