Contamination of eggs by Salmonella Enteritidis and Salmonella Typhimurium in experimentally infected laying hens in indoor cage-free housing.

Authors: Gast, Richard; Jones, Deana; Guraya, Rupinder - Rupa; ANDERSON, KENNETH - North Carolina State University; KARCHER, DARRIN - Purdue University

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2021
Publication Date: 9/12/2021
Citation: Gast, R.K., Jones, D.R., Guraya, R., Anderson, K.E., Karcher, D.M. 2021. Contamination of eggs by Salmonella Enteritidis and Salmonella Typhimurium in experimentally infected laying hens in indoor cage-free housing. Poultry Science. 100(11). https://doi.org/10.1016/j.psj.2021.101438.
DOI: https://doi.org/10.1016/j.psj.2021.101438

Interpretive Summary: Humans can become infected with Salmonella after consuming contaminated eggs produced by infected laying hens. Salmonella Enteritidis is deposited inside eggs when it invades reproductive organs of infected hens. Diverse housing systems are used for laying hens, but their full food safety consequences remain uncertain The present study assessed the frequency of internal contamination of eggs with Salmonella following experimental infection of laying hens in indoor cage-free housing. Groups of hens were housed on wood shavings in isolation rooms simulating commercial cage-free barns with nest boxes and perches. One-third of the hens in each room were orally infected with either S. Enteritidis or S. Typhimurium (another strain which is also sometimes associated with egg-borne disease transmission). During the interval from 5-30 days after infection, all eggs laid in either the nest boxes or on the flooring substrate were collected and tested for the presence of Salmonella in the combined yolk and albumen. Contaminated eggs were laid between 8 and 26 days after infection. Hens infected with S. Enteritidis laid significantly more contaminated eggs (3.4%) than those infected with S. Typhimurium (1.2%). The contamination frequencies of eggs laid in nest boxes or on the floors were not significantly different. These results demonstrated that infection of a relatively small proportion of hens in cage-free housing with invasive Salmonella strains can lead to egg contamination over a period of nearly a month after exposure.

Technical Abstract: Contaminated eggs are a leading source of human Salmonella infections and this problem continues to challenge public health authorities and egg industries around the world. Salmonella invasion of the ovaries and oviducts of infected laying hens can result in bacterial deposition inside the edible portions of developing eggs. The introduction, persistence, and transmission of salmonellae in commercial egg-laying flocks are influenced by flock management practices, but the food safety ramifications of different types of laying hen housing remain unresolved. The present study assessed the frequency of internal contamination of eggs after experimental Salmonella Enteritidis and S. Typhimurium infection of laying hens in indoor cage-free housing. Groups of 72 hens were housed on wood shavings in isolation rooms simulating commercial cage-free barns with community kick-out nest boxes and perches and 1/3 of the hens in each room were orally inoculated with 8.0 × 10e7 cfu of 2-strain mixtures of either S. Enteritidis (2 rooms) or S. Typhimurium (2 rooms), and the entire internal contents of all eggs laid 5-30 d post-inoculation in nest boxes or on the flooring substrate were cultured to detect Salmonella. Contaminated eggs were laid between 8 and 28 d post-inoculation. The contamination frequencies associated with the two egg collection locations were not significantly different (P < 0.05 in Fisher’s exact test). The overall incidence of S. Enteritidis isolation from eggs (3.41%) was significantly (P = 0.0005) greater than S. Typhimurium (1.19%). These results demonstrate that oral infection of a relatively small proportion of laying hens in indoor cage-free housing with invasive Salmonella serovars can result in the production of internally contaminated eggs at low frequencies over a period of nearly a month post-inoculation.