Intranasal immunogenicity of a Delta cya Delta crp-pabA mutant of Salmonella enterica serotype Typhimurium for the horse.

This study investigated the effectiveness of a genetically altered strain of Salmonella enterica bacteria (MGN-707) as a nasal vaccine against salmonellosis in horses. The bacteria didn’t cause disease and, after a single administration, induced strong Salmonella-specific antibody responses in the blood and nasal mucus.

Research Objective and Method

• The main purpose of this research was to examine the immunogenicity of a mutant strain of Salmonella enterica (termed MGN-707) in horses when administered intranasally.
• The mutant strain was a Deltacya Deltacrp-pabA variation, whereby specific genes have been deleted or deactivated. Its potential as a vaccine against salmonellosis in horses was the crux of this investigation.
• The assessment involved observing for any signs of disease, monitoring the bacteria presence in feces, and evaluating the specific antibody responses after the vaccination.

Findings – Antibody Response

• The findings revealed that the MGN-707 strain did not cause any obvious illness and could not be found in the horses’ feces post-introduction.
• More significantly, a single dose administration of this mutant stimulated robust Salmonella-specific antibody responses, both in the serum (blood) and the nasal mucosa of the horses.
• By the 25th day post-immunization, signs of strong Salmonella-specific serum antibodies were noted in all studied ponies. These antibodies included immunoglobulin types such as IgGa, IgGb, IgA and IgM.
• Among these responses, IgM reactions to the Salmonella lipopolysaccharide (LPS) seemed to be short-lived. In contrast, other antibodies (IgGa and IgGb) remained at higher levels for a significantly longer time (83 and 140 days, respectively).

Findings – Differences in Antibody Responses

• The detectable antibody responses varied from pony to pony. While most ponies showed a surge of specific nasal mucosal antibody responses composed of mostly IgA and IgM by day 25, one only exhibited specific IgGa and IgGb antibodies.
• In most ponies, specific nasal mucosal IgA persisted until day 69. However, a second immunization administered on day 140 resulted in even stronger nasal mucosal IgA responses, even in the pony that initially failed to produce an IgA response.

Conclusion and Implications

• At the end of the experiment, IgA and IgGb were chiefly found in jejunal antibody responses, while vaginal responses were predominantly IgA. This confirmed the existence of a common mucosal immune system in equids (horses).
• The results suggest that the S. typhimurium Deltacya Deltacrp-pabA mutant may be potentially beneficial as a nasal vaccine against salmonellosis in horses.