DNA circles with cruciforms from Isospora (Toxoplasma) gondii

Borst, Piet; Overdulve, J. P.; Weijers, P.J.; Fase-Fowler, F.; Berg, M van den

doi:10.1016/0167-4781(84)90128-3

Cited by 54 publications

(19 citation statements)

References 35 publications

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“…61,1997 EXTRACHROMOSOMAL DNA IN THE APICOMPLEXAConservation Snap-back and cross-hybridization experiments with fragments from the IR of the malarial circle provided evidence for conservation of the rDNA palindrome in two other genera of apicomplexans, namely, T. gondii and Eimeria tenella (122). These observations confirmed the suggestion of Borst et al (10) that the cruciform structure they observed in T. gondii circular DNA by electron microscopy was derived from palindromic rRNA genes. Hybridization and PCR experiments have also detected sequences corresponding to rpoB/C, tufA, ORF470, and trn in T. gondii and E. tenella, organized in the same way as in P. falciparum (19a).…”

Section: Codon Usagesupporting

confidence: 79%

Extrachromosomal DNA in the Apicomplexa

Wilson¹,

Gardner²,

Rangachari³

et al. 1993

Toxoplasmosis

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Section: Codon Usagesupporting

confidence: 79%

Extrachromosomal DNA in the Apicomplexa

Wilson¹,

Gardner²,

Rangachari³

et al. 1993

Toxoplasmosis

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“…1, both spiramycin and azithromycin showed no effect after 1 day of treatment and only slight inhibition after 2 days. However, parasite growth was profoundly inhibited after 4 days with 50% inhibitory concentrations (IC50s) of 40 ng/ml for spiramycin and 12 ng/ml for azithromycin. Additional experiments ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Comparison of mutants of Toxoplasma gondii selected for resistance to azithromycin, spiramycin, or clindamycin

Pfefferkorn

Borotz

1994

Antimicrob Agents Chemother

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Azithromycin and spiramycin markedly inhibited the growth of Toxoplasma gondii in cultured human fibroblasts. However, 3 days of treatment were required to reveal their full antitoxoplasma activity. This delayed onset of inhibition was similar to that previously reported for clindamycin. Mutants of T. gondii resistant to azithromycin (AziR_l) and spiramycin (SprR-1) were isolated and compared with a previously described mutant resistant to clindamycin (ClnR-2). Mutant ClnR-2 was cross-resistant to all three antibiotics, while AziR_1 was cross-resistant only to spiramycin and SprR-1 was cross-resistant only to azithromycin. In short-term studies of protein synthesis by freshly prepared extracellular parasites, clindamycin and azithromycin were effective only at concentrations much greater than their 50% inhibitory concentrations in infected cultures and the resistant mutants did not differ from the wild type in antibiotic sensitivity. Thus, protein synthesis on cytoplasmic ribosomes of the parasite did not seem to be the target of these antibiotics. To determine whether mitochondrial protein synthesis in T. gondii was inhibited by clindamycin or azithromycin, wild-type parasites were grown in cultured cells in the presence of antibiotic concentrations well above the 50%o inhibitory concentrations. Mitochondrial function, measured by oxygen uptake per purified extracellular parasite, did not decrease substantially, after the parasites had multiplied 11-fold in the presence of antibiotic.Thus, mitochondrial protein synthesis did not seem to be the target of clindamycin or azithromycin. An alternative target is protein synthesis in the putative apicomplexan organelle that has a 35-kb genome.Toxoplasmic encephalitis is common among AIDS patients. The standard treatment of this opportunistic infection with pyrimethamine and sulfadiazine is generally effective. However, since many AIDS patients cannot tolerate prolonged administration of these drugs (11), alternative treatments are needed. Among the antibiotics known to be active against Toxoplasma gondii are the lincosamide clindamycin and the macrolides spiramycin and azithromycin. Clindamycin reduces mortality in infected mice (1,12,18) and, in combination with pyrimethamine, is as effective as pyrimethamine-sulfadiazine in the treatment of toxoplasmic encephalitis in AIDS patients (7,14). Spiramycin is active against murine toxoplasmosis (2) and is thought to reduce the incidence and severity of congenital disease when used to treat women who acquired toxoplasmosis during pregnancy (17). Azithromycin reduces mortality in experimental murine toxoplasmosis (2). The mechanism of action of these antibiotics against T. gondii is unknown. An understanding of how they exert their antiparasitic activity might allow the design of more potent derivatives. One way to approach the mechanism of action is to characterize antibiotic-resistant mutants. We have isolated a mutant of T. gondii that is markedly resistant to clindamycin (21) and describe here mutants selected for resis...

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“…Some of these are likely to be synthesized on noncytoplasmic ribosomes, but none is sensitive to macrolide antibiotics. In addition to the cytoplasmic ribosomal RNA genes encoded within the nuclear genome, T. gondii, like other coccidian parasites (35), appears to contain at least two additional classes of ribosomal RNA genes, encoded by the mitochondrial genome (present as a tandemly repeated 6-kb linear sequence in Plasmodium species [26]), and a plastid-like genome (a 35-kb circular molecule; [9,29,36,37]). At this stage it is not possible to directly link the cycloheximide-resistant spots with either the mitochondrion or the plastid-like genomes, but the observation that the Plasmodium mitchondrial DNA is much more heavily transcribed than the 35-kb plastid-like circle (Vaidya, A., personal communication) argues in favor of a mitochondrial origin (38).…”

Section: Discussionmentioning

confidence: 99%

Inhibition of cytoplasmic and organellar protein synthesis in Toxoplasma gondii. Implications for the target of macrolide antibiotics.

Beckers¹,

Roos²,

Donald³

et al. 1995

J. Clin. Invest.

117

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IntroductionWe Combining cycloheximide treatment with two-dimensional gel analysis revealed a small subset of parasite proteins likely to be synthesized on mitochondrial ribosomes. Synthesis of these proteins was inhibited by 100 jM tetracycline, but not by 100 jpM azithromycin or clindamycin. Ribosomal DNA sequences believed to be derived from the T. gondii mitochondrial genome predict macrolide/lincosamide resistance. PCR amplification of total T. gondii DNA identified an additional class of prokaryotic-type ribosomal genes, similar to the plastid-like ribosomal genes of the Plasmodium falciparum. Ribosomes encoded by these genes are predicted to be sensitive to the lincosamide/macrolide class of antibiotics, and may serve as the functional target for azithromycin, clindamycin, and other protein synthesis inhibitors in Toxoplasma and related parasites. (J. Clin. Invest. 1995. 95:367-376)

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DNA circles with cruciforms from Isospora (Toxoplasma) gondii

Cited by 54 publications

References 35 publications

Extrachromosomal DNA in the Apicomplexa

Extrachromosomal DNA in the Apicomplexa

Comparison of mutants of Toxoplasma gondii selected for resistance to azithromycin, spiramycin, or clindamycin

Inhibition of cytoplasmic and organellar protein synthesis in Toxoplasma gondii. Implications for the target of macrolide antibiotics.

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