Enteric fever (typhoid and paratyphoid fever) is caused by 4 enteric bacteria, namely, S. Typhi, S. Paratyphi A, S. Paratyphi B and S. Paratyphi C. The disease is still an important infectious disease problem in less developed countries. Diagnosis is based on the isolation of Salmonellae spp. Frkom various body specimens and widal test. However

the former is time consuming and sometimes can give false negative owing to prior antibiotic therapy. The latter is unreliable especially in endemic therapy. The latter is unreliable especially in endemic area because crude unpurified antigen was used. In attempt to reduce cross-reactivities, species-specific monoclonal antibodies (MAbs) were produced. These reagents are useful for the identification and purification of these 4 corresponding salmonell antigens to be used for the diagnosis of enteric fever. The immunogen used for the immunization of BALB/c mice was "affinity purified" protein which was prepared by passing crude bacterial protein through an affinity column made from sepharose conjugated to IgG antibodies against corresponding partially purified bacterial protein. Several highly specific hybrid clones were obtained, 10 for s. Typhi, 72 for s. Paratyphi A, 9 for S. Paratyphi B and 8 for S. Paratyphi C. With the exception of MAbs to S. Paratyphi C, all other MAbs did not cross-react with the antigens of other Enterobacteriaceae in the indirect ELISA and immunoblot analysis. MAbs to S. Paratyphi C cross reacted with S. Choleraesuis. MAbs to S. Typhi, S. Paratyphi A and S. Paratyphi B were specific yp 52 kd protein components, while MAbs to S. Paratyphi C were specific to 61 kd protein components of their corresponding bacteria and 59 kd protein components of S. Choleraesuis. When acute sera from patients with typhoid, paratyphoid A and paratyphoid B were allowed to react with whole cell (WC) antigens freshly prepared from their corresponding bacteria in the immunoblot, specific IgM antibody to 52 kd protein was detected. these results suggested that the specific components seem to be highly immunogenic. with the combination of highly specific MAbs and recombination DNA technology, the specific DNA probe can be readily constructed and used for rapid diagnosis of this disease. Moreover, purified protein or synthetic peptide of the specific component can be readily obtained and also used in the immunoassay (S) or for studying pathogenesis, protective immunity of this disease as well as Salmonellae taxonomy.