Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2001
Publication Date: 5/1/2002
Citation: Jones, D.R., Anderson, K.E., Curtis, P.A., Jones, F.T. 2002. Microbial contamination in inoculated shell eggs: 1. Effects of layer strain and hen age. Poultry Science. 81:715-720.
Interpretive Summary: In recent history, foodborne illnesses have been linked to shell eggs causi them to be identified as a microbial food safety concern. A flock of histo strain hens along with a current commercial stock were reared in the same environment. All hens were subjected to a molt at 62 wks of age. A molt involves enacting a short, controlled fast which results in the loss of the efeathers and cessation of egg production. Molting is utilized to rejuvena the production of high quality shell eggs. Shell eggs collected throughout the cycle of the flock were inoculated with bacteria and sampled at four locations within the egg. The results of this study found that Salmonella growth and contamination levels were dependent on hen age. Pseudomonas fluorescens growth and contamination within the egg was dependent on shell egg quality. Salmonella enteritidis contamination levels remained the same before and immediately after the molt. Pseudomonas fluorescens was better able to traverse the shell membranes and contaminate the contents of the e compared to Salmonella enteritidis. This study also found that levels of microbial contamination in shell eggs varied among the different strains of hens suggesting that genetic selection can also play a role in the microbia integrity of the egg.
Technical Abstract: Three Ottawa control strains and a current commercial laying stock were reared and housed under identical environmental and management conditions. Eggs were collected from each strain when hens were 32, 45, 58, 71 and 84 wks of age. The eggs were inoculated with Salmonella enteritidis (Se), Pseudomonas fluorescens (PF), or a combination of the two. After storage at 26§C, bacterial counts were obtained from the exterior shell surfaces (rinse), the air cell, the egg contents, and the shell structure. Se and PF survived at different rates on the shell surface with as much as a 1 log difference during a given collection period. Egg content counts tended to be higher than eggshell counts in PF, while the opposite was true for Se. These data suggest that PF is a primary invader of eggs more capable of contaminating egg contents through the shell membranes than Se. Both the PF and the Se data suggest that bacterial contamination of air cells, shells, and egg contents is more easily achieved in eggs from older hens than from younger hens. There were also differences between the strains. Control Strain 10 consistently maintained a lower level of contamination for both organisms in each sampling location. The overall results of this study suggest that genetic selection has altered the ability of eggs to resist microbial contamination and that screening for microbial integrity should be considered in the selection process among the laying egg breeders.