Evaluating two live-attenuated vaccines against Salmonella enterica serovar Reading in turkeys: reduced tissue colonization and cecal tonsil transcriptome responses

Vaccines that cross-protect across serovars of <i>Salmonella enterica</i> (<i>Salmonella</i>) would be a beneficial intervention against emerging and persistent <i>Salmonella</i> isolates of concern for the turkey industry. The 2017-2019 foodborne outbreak of <i>Salmonella enterica</i> serovar Reading (<i>S</i>. Reading) revealed the need for effective control of this serovar in turkey production. This study evaluated two live-attenuated <i>Salmonella</i> vaccines, an internally developed cross-protective vaccine and a commercially available vaccine, against an outbreak-associated strain of <i>S</i>. Reading in turkeys. At 1 day and 3 weeks of age, male turkey poults were either mock-vaccinated with phosphate buffered saline (PBS) or given one of the vaccines by oral gavage (primary and booster) or aerosol spray (primary) then drinking water (booster). At 7 weeks of age, poults were challenged with 10⁹ colony forming units (CFU) of <i>S</i>. Reading; a mock-vaccinated group was mock-challenged with PBS. Colonization of the cecal contents and cecal tonsil was 1.5-3 log₁₀ CFU/g lower in vaccinated birds than mock-vaccinated birds at 7 and/or 14 days post-inoculation (DPI). <i>Salmonella</i> dissemination to the spleen was significantly reduced by both vaccines. Gene expression of intestinal transporters (such as <i>SCNN1B</i> and <i>SLC10A2</i>) and tight junction proteins was significantly decreased in the turkey cecal tonsil transcriptome at 2 DPI with <i>S</i>. Reading. Vaccination with either vaccine mitigated most cecal tonsil gene expression responses to <i>S</i>. Reading challenge. Therefore, both the internally developed vaccine and commercial vaccine were cross-protective against colonization and dissemination, and both were able to limit transcriptional changes from challenge in intestinal health-related genes in the cecal tonsil, thereby providing vaccination efficacy and impact data against <i>S</i>. Reading in turkeys.