Intracellular autolytic whole cell Salmonella vaccine prevents colonization of pathogenic Salmonella Typhimurium in chicken

Salmonella enterica (SE) is a major foodborne bacterial pathogen in the United States, commonly found as the normal flora of various animals that is attributed to causing at least 1.2 million infections annually. Poultry plays a major role in disseminating SE through direct contact with live animals and consumption of contaminated products. Vaccinating poultry against SE is a sustainable approach that can reduce SE in the host, preventing future infections in humans. An intracellular autolytic SE serovar Typhimurium vaccine (STLT2^{+P13+19}) was developed by integrating genes 13 (holin) and 19 (lysozyme) of bacteriophage P22 into the bacterial chromosome. These were inserted downstream of sseA, an SPI-2 chaperone in SE that expresses during the intracellular phase of SE. Intracellular viability of STLT2^{+P13+19} reduced by 94.42% at 24 hr compared to the wild type in chicken macrophage cells (HD-11), whereas growth rate and adhesion ability remained unchanged. Inoculating STLT2^{+P13+19} in HD-11 significantly enhanced the relative log fold expression of genes associated to production of pro-inflammatory cytokines (IL-1β, IL-6, IL-8, IL-10, IL-12 p40, IL-18, and GM-CSF) and Toll-like-receptors (TRL-3 and 7). Vaccination of an in vivo chicken model demonstrated significant changes in secretion of iNOS, IL-6, IL-8, IL-12, and TNF-α, as well as a reduction in the intestinal colonization of SE serovar Typhimurium. Microbiome analysis of cecal fluid using 16S rRNA gene sequencing also showed modulation of intestinal microbial composition, specifically a decrease in relative abundance of Proteobacteria and increasing Firmicutes. This study provides insight into a novel vaccine design that could make food products safer without the use of synthetic compounds.