Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2000
Publication Date: 2/8/2001
Interpretive Summary: Live vaccines that are used to decrease Salmonella on the carcasses of broilers have been approved. In these studies, we show that a S. typhimurium vaccine genetically engineered to decrease its ability to cause disease did not decrease egg contamination by S. enteritidis. In addition, immunized birds produced more contaminated eggs than did non-immunized birds. Thus, it must be considered that release of live Salmonella vaccines have the potential to increase egg contamination. Results indicate that live Salmonella vaccines used in egg-laying birds as aids for decreasing organ invasion should be directly assessed for their ability to decrease egg contamination.
Technical Abstract: We investigated the ability of a Salmonella enterica serovar Typhimurium (S. typhimurium) aroA vaccine (ST-AV) to prevent egg contamination in chickens after oral challenge with S. enteritidis. Immunized birds had fewer positive ovary/oviduct pools and lower CFU/gram cecal contents of S. enteritidis than did non-immunized birds. However, the number of positive intestinal (duodenum, jejunum, ileum) and organ (spleen, kidney, liver) pools following challenge were nearly the same for immunized and non-immunized birds. Most importantly, aroA vaccinated birds produced more contaminated egg pools than did vaccinates. Humoral immune responses as measured by ELISA with LPS from each serovar as primary antigen detected significantly higher levels of circulating antibodies in vaccinates, but the response was not serotype specific. These results suggest that heterologous aroA vaccines might not be effective for reducing egg contamination by S. enteritidis even when the reproductive tract yields fewer CFU. Most importantly, results strongly suggest that GE-MLVs should be tested for their ability to decrease egg contamination directly if they are to be marketed to the layer industry.