The effects of stress on respiratory disease and transient colonization of turkeys with Listeria monocytogenes Scott A.
Listeria monocytogenes contaminates poultry processing plants due to its ubiquitous nature and high resistance to disinfection. The sources of the persistent, biofilm-forming strains that colonize processing plants are unknown. The purpose of this study is to determine if intrinsic colonization of turkeys is a possible source of contamination. Male poults were subjected to cold stress from 4-12 days of age; poults were unchallenged or were exposed to an aerosol and oral challenge of either an avian pathogenic strain of Escherichia coli (Ec), the Scott A strain of L. monocytogenes (Lm), or to a combination (Ec-Lm). At 7 wk, all cold-stressed poults were treated with an immunosuppressive dose of dexamethasone (Dex) and exposed to the same bacterial challenges. Birds were necropsied at 1 wk and 2 wk post-Dex treatment. Percent mortality, body and organ weights, and airsacculitis scores were determined. Liver and knee synovial tissues were sampled, using transport swabs, and cultured by direct plating, pre-enrichment, and Taqman real-time PCR. There were no significant differences in cumulative mortality, and airsacculitis scores were variable but tended to be decreased by cold stress. Relative weights of liver and heart were increased, whereas body weights, and spleen and bursa relative weights, were decreased following all challenges. Listeria monocytogenes was isolated from up to 50% of liver or knee synovial tissues, using pre-enrichment followed by culturing methods, and from up to 67% of knee synovial tissues using pre-enrichment followed by real-time PCR at 1 wk post-challenge. The higher percentages of positive birds, detected by real-time PCR rather than by culture, and the negative results at 2 wk post-challenge suggest that the birds experienced a transient infection that was cleared by the immune system. These results suggest that environmentally acquired L. monocytogenes can transiently colonize the liver and synovial tissues of stressed turkeys and may be a sporadic source of contamination of processing plants.