Abstract: ObjectiveTo investigate the median lethal dose(LD₅₀)and bio logical distribution of an attenuated Salmonella typhimurium strain,SA-2F5,with the 2F5 epitope of human immunodeficiency virus type 1(HIV-1)in BALB/c mice.MethodsBALB/c mice were randomly divided into eight groups,infected intragastrically with PBS or 10⁴~10¹⁰ colony forming units(CFU)of S.typhimurium SA-2F5 and monitored over a 30-day period,and LD₅₀ value was calculated.For detecting the presence of the bacteria in tissues,BALB/c mice were randomly divided into two groups and ino culated intragas-trically with 10⁷ CFU SA-2F5 or PBS.Livers,spleens and mesentericly mphnodes were isolated from inoculated mice on 3, 9,16 or 30 days post-inoculation and numbers of live bacteria in each organ were counted.ResultsLD₅₀ of SA-2F5 to BALB/c mice was 1.45×10⁹ CFU.The recombinant Salmonella strain could proliferate in livers,spleens and mesenteric lymph nodes of infected mice.The numbers of live bacteria within livers,spleens and mesenteric lymph nodes were 5.38×10⁴ CFU,4.87×10⁴CFUand 9.08×10³CFU respectively on 3 days post-inoculation,and decreased to 7.35×10² CFU, 7.50×10² CFU and 3.00×10²CFU respectively on 9 days post-inoculation.The situation of 16 day was similar to that of 9 days.There was no bacterium presentin above organs on 30 days post-inoculation,except 2.1×10² CFU in mesenteric lymph nodes.ConclusionCompared with wild type strains,the recombinant Salmo nella was significantly attenuated and had a broad distribution in tissues of the BALB/c mice.