Distribution of Salmonella paratyphi A outer membrane protein X gene and immune-protective effect related to its recombinant expressed products / 中华流行病学杂志

ABSTRACT

Objective To determine the distribution and sequence conservation of outer membrane protein X (ompX) gene in Salmonella paratyphi A isolates as well as the immunogenicity and irnmono-protection of ompX gene products.Methods OmpX gene in Salmonella paratyphi A isolates was detected by PCR and the amplification products were sequenced after the T-A cloning process.OmpX gene product was expressed with E.coli expression system and the expressed rOmpX was extracted by Ni-NTA affinity chromatography.SDS-PAGE and Bio-Rad Gel Image Analyzer were applied to examine the expression and yield of rOmpX.Both antigenicity and immune-reactivity of rOmpX were detected by immune-diffusion test,ELISA and Western blot assay.The immuneprotective effect of rOmpX against infection of Salmonella paratyphi in mice was determined and the agglutinative titers of sera from rOmpX-immunized mice was measured by micro-Widal' s test.Results All the tested Salmonella paratyphi A isolates had ompX gene with high nucleotide or amino acid sequence identity (99.2％-100.0％ or 98.4％-100.0％).When rOmpX was induced to rabbits to produce high level antibody and combined with antiserum against whole cell of Salmonella paratyphi A,the results displayed a positive Western hybridization signal.Results from ELISA demonstrated that 95.6％ (65/68) of the serum samples from paratyphoid-A patients were positive on rOmpX antibody.Mice that were immunized with 100 μg or 200 μg rOmpX displayed an immune-protective rate of 93.3％ (14/15) or 100.0％ (15/15).Sera from those rOmpX-immunized mice provided 1 ∶ 10-1 ∶ 40 agglutination titers in both H antigens of Salmonella paratyphi A and Salmonella typhi.Conclusion The recombinant expression product of ompX gene could be used as a candidate antigen for developing genetic engineering vaccines against Salmonella paratyphi A infection.