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.
Highlights
In poultry, the infectious bacteria Salmonella enterica subsp. enterica can be divided in two broad groups of serovars on the basis of pathogenesis and infection biology (EFSA, 2004)
Western blotting confirmed the lack of reactivity of the waaL mutant LPS with an anti-O9 monoclonal antibody indicating that the LPS lacked the O-antigen (Figure 1B)
The mutant strain displayed a rough-phenotype whereas the wild type strain displayed smooth-phenotype since it did not cause agglutination (Figure 1C)
Summary
The infectious bacteria Salmonella enterica subsp. enterica can be divided in two broad groups of serovars on the basis of pathogenesis and infection biology (EFSA, 2004). Enterica can be divided in two broad groups of serovars on the basis of pathogenesis and infection biology (EFSA, 2004). One group, containing the serovar Gallinarum biovars Pullorum and Gallinarum, causes a severe systemic typhoid-like disease in a restricted range of hosts (Barrow and Freitas Neto, 2011). A DIVA Vaccine against Salmonella Pullorum containing the serovar Enteritidis, causes gastrointestinal disease in a wide range of hosts including humans. Salmonella Enteritidis is the cause of the food-borne salmonellosis pandemic in humans, in part because it has the unique ability to contaminate poultry products without causing discernible illness in the birds infected (Guard-Petter, 2001). There is a need for methods that protect broilers, from day-of-hatch until slaughter age, against infection with Salmonella Pullorum, as well as to reduce the contamination of the food-borne serotype Salmonella Enteritidis
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