Tissue Colonization and Egg and Environmental Contamination Associated with the Experimental Infection of Cage-Free Laying Hens with Braenderup.

In 2018, a national recall of shell eggs in the United States occurred due to human illness caused by Braenderup. Although previous studies have identified Braenderup in laying hens and the production environment, little is known about the ability of this serovar to infect laying hens and contaminate eggs. The objective of this study was to examine the invasiveness of Braenderup in laying hens as well as its ability to persist in the production environment. Specific-pathogen-free laying hens (four trials; 72 hens/trial) were orally challenged with 10 colony-forming units of Braenderup. On day 6 postinoculation, half of the challenged hens were euthanatized, and samples of ileocecal junction (sections above and below it, and portions of both ceca), liver, spleen, ovary, and oviduct tissues were collected and cultured for Braenderup. Egg and environmental (nest box swaps and substrate (litter)) samples were collected days 7-20 postinoculation (Trials 1 and 2; excluding weekends) and days 7-27 postinoculation (Trials 3 and 4; excluding weekends) to detect Braenderup. Recovery of Braenderup was highest in ileocecal tissue samples (11.1%-33.3%; < 0.05), with little to no recovery in other collected tissue samples. Braenderup was detected in a small number of shell emulsions (0%-2.9%; < 0.01) and recovered in Trial 1 at a high rate (92.5%; < 0.0001) in the substrate composite samples; however, recovery of Braenderup was low in the other egg and environmental samples. These trials indicate that Braenderup is not an invasive serovar for cage-free laying hens, especially when compared to serovars of concern to the egg industry. However, it may persist in the environment at low levels.