DIFFERENTIATION OF TOXOPLASMA-GONDII FROM CLOSELY RELATED COCCIDIA BYRIBOPRINT ANALYSIS AND A SURFACE-ANTIGEN GENE POLYMERASE CHAIN-REACTION

The tachyzoite of the human pathogen Toxoplasma gondii is morphologica lly indistinguishable from the proliferative stages of some other zoon otic coccidia, including Sarcocystis. To determine the identity of suc h coccidia obtained from human tissues and other sources, we compared riboprints (through restriction enzyme analysis of the polymerase chai n reaction [PCR]-amplified small subunit rRNA gene) of the following p rotozoa: the RH and ts-4 strains of T. gondii, lines OH3 and S11, whic h are two recently isolated T. gondii-like parasites from Brazil, Neos pora caninum, Sarcocystis species, and the malarial parasite Plasmodiu m berghei. In addition, the protozoan genomes were examined by PCR for homologs of surface antigen genes of T. gondii, and by Southern hybri dization to the heterologous rRNA gene probe pSM 389. Strains OH3, S11 , ts-4, and RH shared identical riboprints, and OH3, S11, and ts-4 hav e p22 and p30 surface antigen gene structures similar to RH. In contra st, riboprints for N. caninum and T. gondii differ with respect to Dde 1 sites, and moreover, their genomes vary significantly from one anot her at both the p22 and p30 gene loci. The riboprints of Sarcocystis a nd P. berghei differ markedly from T. gondii and N. caninum and from e ach other. Bam HI pSM 389 restriction fragment length polymorphisms di fferentiate ts-4 from RH, OH 3, and S11. Our results confirm that OH3 and S11 are indeed T. gondii, but that N. caninum and T. gondii are li kely to be separate species, thereby resolving previous uncertainties concerning the identity of these parasites. Together, the variation in riboprints and surface antigen gene structure reflects the phylogenet ic diversity among these coccidia, and in addition, confirms the value of riboprinting in the identification of apicomplexan parasites such as T gondii.