Virulence evaluation and potential use as vaccine of Salmonella enterica mutants for nucleoid associated proteins

Salmonella enterica is a gram-negative bacillus belonging to the family Enterobacteriaceae responsible for major economic and public health losses, may cause diseases to humans ranging from gastroenteritis to systemic infections and in animals, causing great economic losses. The most commonly isolated serovar in salmonellosis outbreaks in Brazil, Europe and the United States, are Enteritidis and Typhimurium, being eggs and other products derived from chicken the main source of infection. One way to control infections caused by Salmonella is by vaccination, a strategy that is already being used in several countries, although there is still need to improve those vaccines. Here we emphasize the use of wild strains of S. enterica, performing genotypic and phenotypic characterization of these strains, and compared with mutants for nucleoid associated proteins obtained from them, to test the feasibility of using these mutants as vaccine vectors. The wild-type strains had their genome sequenced. Starting from this wild-type strains we obtained mutants for the genes fis, hupA e hupB, intendind to verify their potential use as live-attenuated vaccines. The proteins encoded by these genes are associated to the bacterial nucleoid and directly or indirectly influences expression of virulence genes and when deleted may lead to different levels of attenuation. The S. enterica Typhimurium mutants for the fis gene showed to be sufficiently attenuated and therefore capable of being tested as live attenuated vaccines. S. enterica Enteritidis mutants for hupA and hupB genes were also obtained, although the single mutants (hupA or hupB) were not attenuated, the double mutant hupAB showed to be very attenuated, allowing doses greater than 109 CFU. Additionally, the attenuated mutants obtained in this study were able to elicit an immune response capable of protecting BALB / c mice against a challenge with wild type strain. These results clearly demonstrate that the strains developed herein have potential for use as live-attenuated vaccines (AU)