Pj. Brindley et al., DIFFERENTIATION OF TOXOPLASMA-GONDII FROM CLOSELY RELATED COCCIDIA BYRIBOPRINT ANALYSIS AND A SURFACE-ANTIGEN GENE POLYMERASE CHAIN-REACTION, The American journal of tropical medicine and hygiene, 48(3), 1993, pp. 447-456
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.