Serodiagnosis of Toxoplasma gondii infection in cats by enzyme-linked immunosorbent assay using recombinant SAG1

The gene encoding surface antigen I (SAG1, P30) of Toxoplasma gondii (T gon dii) was cloned into the plasmid pGEX-4T-3 and subsequently expressed in Es cherichia coli (E. coli) as a glutathione-S-transferase (GST) fusion protei n. The recombinant SAG1 (rSAG1) was refolded using 8 M urea solution follow ed by dialysis and thereafter evaluated in an enzyme-linked immunosorbent a ssay (ELISA) for serological diagnosis of toxoplasmosis. The test sera were adsorbed with GST to block non-specific reactivity to the GST-SAG1 fusion protein. The ELISA with rSAG1 was able to differentiate very clearly betwee n sera from cats or mice experimentally infected with T gondii and sera fro m normal cats or mice. The ELISA detected no cross-reactivity with sera fro m mice experimentally infected with the closely related parasite Neospora c aninum (N. caninum). Some 193 cat sera were tested for antibodies to T gond ii, out of which 40 (20.7%) reacted positively by ELISA with the rSAG1 whil e another 79.3% cats reacted negative to the assay. Both positive and negat ive sera were confirmed by Western blot analysis. The results of ELISA were in agreement with those of a commercially available latex agglutination te st (LAT) kit, although the former had higher titers than the latter. (C) 20 01 Elsevier Science B.V. All rights reserved.