Safety, Protective Immunity, and DIVA Capability of a Rough Mutant Salmonella Pullorum Vaccine Candidate in Broilers

Abstract

Salmonella enterica subsp. enterica serovar Gallinarum biovar Pullorum (Salmonella Pullorum) is highly adapted to chickens causing an acute systemic disease that results in high mortality. Vaccination represents one approach for promoting animal health, food safety and reducing environmental persistence in Salmonella control. An important consideration is that Salmonella vaccination in poultry should not interfere with the salmonellosis monitoring program. This is the basis of the DIVA (Differentiation of Infected and Vaccinated Animals) program. In order to achieve this goal, waaL mutant was developed on a spiC mutant that was developed previously. The safety, efficacy, and DIVA features of this vaccine candidate (Salmonella Pullorum ΔspiCΔwaaL) were evaluated in broilers. Our results show that the truncated LPS in the vaccine strain has a differentiating use as both a bacteriological marker (rough phenotype) and also as a serological marker facilitating the differentiation between infected and vaccinated chickens. The rough mutant showed adequate safety being avirulent in the host chicks and showed increased sensitivity to environmental stresses. Single intramuscular immunization of day-old broiler chicks with the mutant confers ideal protection against lethal wild type challenge by significantly stimulating both humoral and cellular immune responses as well as reducing the colonization of the challenge strain. Significantly lower mean pathology scores were observed in the vaccination group compared to the control group. Additionally, the mutant strain generated cross-protection against challenge with the wild type Salmonella Gallinarum thereby improving survival and with the wild type Salmonella Enteritidis thereby reducing colonization. These results suggest that the double-mutant strain may be a safe, effective, and cross-protective vaccine against Salmonella infection in chicks while conforming to the requirements of the DIVA program.

Controversy Surrounding the Function of SpiC Protein in Salmonella: An Overview

“…The mutant strain generated cross-protection against challenge with the wild-type Salmonella Gallinarum. These results suggest that the double-mutant strain may be a safe, effective, and cross-protective vaccine against Salmonella infection in chicks while conforming to the requirements of the DIVA program (Guo et al, 2017).…”

Efficacy of a nanoparticle vaccine administered in-ovo against Salmonella in broilers

“…To prevent Salmonella infections and the economic burden it brings, the poultry industry employs the use of Salmonella vaccines, but currently, commercial vaccines have certain disadvantages. Live vaccines are not preferred due to the ability of the live strain to regain its virulence and spread through shedding, interfere with the salmonellosis monitoring program [ 4 ], and strict cold chain requirement to preserve their function. Killed vaccines are preferred, but the intramuscular route of administration is time-consuming, increases tissue damage, and requires additional vaccine administration costs.…”

Evaluation of Safety and Protective Efficacy of a waaJ and spiC Double Deletion Korean Epidemic Strain of Salmonella enterica Serovar Gallinarum

“…Our result showed that SG005 and SG005Δ spiC were agglutinated with O9 factor rabbit antiserum but SG005Δ waaJ and SG005Δ waaJ Δ spiC were not, indicating that the waaJ deletion strain did not contain O9 antigen. We performed the acriflavine agglutination test, which is used to detect the rough phenotype of bacteria ( 21 ). Our results were consistent with our expectations.…”

“…Mixtures were rotated for 1 min and observed for agglutination. The acriflavine agglutination test was performed to detect the rough phenotype characteristic of the deletion strains ( 21 ). Briefly, colonies of a 24-h culture prepared from the deletion strains on LB agar plates were mixed with 20 μl of 0.2% acriflavine on a glass slide.…”