Microbial contamination in inoculated shell eggs: II. Effects of layer strain and egg storage

Three Ottawa control strains and a current commercial laying stock were reared and housed in the same environment. Eggs were collected at 5 different hen ages throughout the 2 production cycles of the flock. The eggs were inoculated with Salmonella Enteritidis (SE), Pseudomonas fluorescens (PF), a combination of the 2, or sterile buffered peptone water and stored up to 5 wk. After storage at room temperature, contamination levels were determined for the exterior surface, air cell, egg contents, and within the shell. Interior, egg contents, and shell contamination levels of SE and PF increased with storage time. There were no apparent increases in the infectivity of SE or PF in the presence of the other organism. PF was a poor survivor on the shell surface under these storage conditions. Throughout the 5-wk storage, eggs from control strain 10 maintained their microbial integrity more effectively. Eggs from control strain 5 and the current commercial stock were more easily contaminated than the other strains. These data suggest that genetic selection has altered microbiological defenses of the eggs produced.