A case study on Salmonella enteritidis (SE) origin at three egg-laying farms and. its control with an S. enteritidis bacterin

In the early 1990s, three egg-laying farms (farms S, T, and B) were thought to have the possibility of Salmonella enteritidis (SE) contamination becau se positive liquid egg samples originated from those farms. The present stu dy was therefore conducted. The first clarification fur SE contamination was the study on the origin of SE contamination including its vertical transmission. The results of SE co ntamination profiling with dust and manure, food materials, dead embryos, a nd residual yolks on hatch day in regular monitoring over a few years were clearly negative. Therefore, we concluded the SE transmission/infection was attributed to horizontal infection in the egg-laying farms but not vertica l transmission from parental stock, hatcheries, growth, or food materials d uring a 7-yr experimental period. Second, we attempted to clarify if administration of an SE bacterin (Layerm une SE) to growth flocks for the egg-laying farms could reduce SE incidence in liquid egg samples from each egg-laying farm. In the first experiment, we compared SE incidence in liquid egg samples fro m vaccinated and nonvaccinated flocks (similar age flocks). SE incidence fr om vaccinated and nonvaccinated flocks showed negative and > 2 most probabl e number (MPN)/100 mi for farm B, < 2 and > 1600 MPN/100 mi for farm S, and negative and > 1600 MPN/100 mi for farm T, respectively. In the second exp eriment, we compared the SE isolation incidence in the liquid egg samples f rom nonvaccinated and newly replaced vaccinated flocks in the same chicken houses from each of the three egg-laying farms. SE incidence in the liquid egg samples was similar to that in the first experiment. Therefore, the SE bacterin may play an important role in reducing the SE incidence of liquid egg samples.