Evaluation of the protective effect of immunization spf DBA/2J mice with selected bacterial, recombinant Hsp60 antigens during Salmonella Enteritidis challenge.

Salmonella Enteritidis is one of the most common causes of food poisoning in humans. Many attempts have been made to develop an effective vaccine against S. Enteritidis for use in poultry, but experiments aimed at the complete elimination of this pathogen from poultry farms have not provided satisfactory results. The development of new generation vaccines against salmonellosis, such as subunit vaccines based on heat shock proteins (HSPs), is strongly justified. The high immunogenicity of Hsp60 isolated from Procaryota, including Salmonella, has been suggested by the presence of IgG anti-Hsp60 antibodies in mice immunized with these proteins. The aim of the studies was to evaluate the protective effects of immunization with recombinant Hsp60 from selected gram-negative bacteria (S. Enteritidis, Escherichia coli, Pasteurella multocida, Histophilus somni) in spf DBA/2 J mice experimentally infected with S. Enteritidis. The study demonstrated that double subcutaneous immunization of mice with a dose of 10 μg rHsp60 induced a specific immune response of IgG antibodies in tested animals. The median lethal dose (LD50) for the murine model spf DBA/2 J orally infected with S. Enteritidis was estimated at 6.84 × 105  cfu/animal. Mice immunized with rHsp60 from gastrointestinal pathogens (S. Enteritidis and E. coli) showed better survival after experimental infection with a 3 × LD50 dose from S. Enteritidis, compared to animals immunized with proteins obtained from respiratory pathogens (P. multocida and H. somni). However, the log-rank analysis did not show significant differences in the survival rates between rHsp60-immunized mice and controls. S. Enteritidis was not isolated any less frequently from internal organs and faeces of rHsp60-immunized mice than from controls. Nevertheless, the level of haptoglobin (but not IL-6) was increased in all mice in which the presence of the pathogen was observed. Bacterial Hsp60 is an interesting candidate for a subunit vaccine, but its use in livestock animals must be further investigated.