Orally delivered chitosan-based Salmonella subunit nanovaccine provides protective immunity against colonization by Salmonella Enteritidis in adult layer chickens.

INTRODUCTION

Salmonella contamination in poultry meat and eggs remains the leading cause of foodborne illnesses in humans. Particularly, Salmonella Enteritidis has been frequently identified as a primary source of contamination in eggs. This study was designed to evaluate the effectiveness of a subunit Salmonella nanovaccine in adult layers.

METHODS

The vaccine was formulated using the mannose-conjugated chitosan nanoparticles (mChitosan-NP) delivery platform, incorporating S. Enteritidis derived outer membrane proteins (OMP) and flagella (Fla) entrapped in mChitosan-NP, and surface-coated with Fla [mChitosan (OMP+Fla)/Fla-NP]. This candidate nanovaccine was administered orally to pullets, raised from day 0 of hatching to adult egg laying age. To determine the dose-dependent efficacy of the nanovaccine, three different doses of antigens (200, 50, and 10 microgram) entrapped in NP were administered four times orally at 4, 10, 16, and 18 weeks of age and challenged at age 25 weeks with 109 CFU S. Enteritidis. Necropsies were performed at 4 and 8 days post-challenge (DPC) infection, and challenge Salmonella load in the cecum, reproductive tract, and eggs was assessed.

RESULTS AND DISCUSSION: Our data revealed that the highest vaccine dose (200 microgram per bird) resulted in a 2.7 log reduction in cecal S. Enteritidis load at DPC4 compared to the control group. Moreover, in the same group, Salmonella was undetectable in the upper and lower reproductive tracts on direct culture method. Flow cytometric analysis revealed an increased frequency of activated recall B cell response. Additionally, enhanced antigen-specific antibody responses were detected at both mucosal and systemic sites, particularly at DPC8. Furthermore, enhanced OMP-specific IgY response in the egg yolk was detected in the nanovaccine-administered birds. Overall, the immune response data were positively associated with the vaccine's efficacy, suggesting that the oral administration of the Salmonella nanovaccine has the potential to reduce the risk of Salmonella transmission in eggs.