PROTECTIVE CAPACITY OF A TEMPERATURE-SENSITIVE MUTANT OF SALMONELLA-ENTERITIDIS AFTER ORAL AND INTRAGASTRIC INOCULATION IN A MURINE MODEL

Temperature-sensitive (ts)mutant E/1/3 of Salmonella enteritidis was selected to evaluate its capacity to induce protective responses after peroral (p.o.) or intragastric (i.g.) inoculation to mice. This ts mutant of coasting phenotype was detected in Peyer's patches until day 4, and in spleen by days 3 and 4 after the mice were inoculated by the p.o. route with 10(10) colony forming units. Peroral immunization induced significant protection from oral challenge with 240 LD50 of the wild-type (wt) strain. Higher protection was achieved when the animals were boosted intraperitoneally after p.o. immunization. Intragastric inoculation with the same dose of the ts mutant increased both the level of protection, and colonization and persistence of the micro-organism in Peyer's patches and spleen. Immunization with a single i.g. inoculation induced 70% protection from p.o. challenge of the animals with the wt S. enteritidis. Two i.g. immunizations with E/1/3 raised the level of protection to 90%. Specific IgG, IgM and IgA antibodies, measured in plasma using a micro-ELISA method, were detected after i.g. immunization with ts mutant E/1/3. In addition, specific antibody-secreting cells were detected by means of an ELISPOT assay in spleen and mesenteric nodes of mice immunized with the ts mutant.