Pfefferkorn E R, Borotz S E
Department of Microbiology, Dartmouth Medical School, Hanover, New Hampshire 03755-3842.
Antimicrob Agents Chemother. 1994 Jan;38(1):31-7. doi: 10.1128/AAC.38.1.31.
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-1) 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% 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.
阿奇霉素和螺旋霉素能显著抑制弓形虫在培养的人成纤维细胞中的生长。然而，需要3天的治疗才能展现出它们完全的抗弓形虫活性。这种抑制作用的延迟出现与先前报道的克林霉素相似。分离出对阿奇霉素（AziR - 1）和螺旋霉素（SprR - 1）耐药的弓形虫突变体，并与先前描述的对克林霉素耐药的突变体（ClnR - 2）进行比较。突变体ClnR - 2对所有三种抗生素都有交叉耐药性，而AziR - 1仅对螺旋霉素有交叉耐药性，SprR - 1仅对阿奇霉素有交叉耐药性。在对新制备的细胞外寄生虫进行蛋白质合成的短期研究中，克林霉素和阿奇霉素仅在浓度远高于其在感染培养物中的50%抑制浓度时才有效，并且耐药突变体在抗生素敏感性方面与野生型没有差异。因此，寄生虫细胞质核糖体上的蛋白质合成似乎不是这些抗生素的作用靶点。为了确定克林霉素或阿奇霉素是否抑制弓形虫的线粒体蛋白质合成，将野生型寄生虫在抗生素浓度远高于50%抑制浓度的情况下在培养细胞中培养。在寄生虫在抗生素存在下增殖11倍后，通过每个纯化的细胞外寄生虫的氧气摄取量来测量的线粒体功能并没有显著下降。因此，线粒体蛋白质合成似乎不是克林霉素或阿奇霉素的作用靶点。另一个作用靶点是具有35 kb基因组的推测顶复门细胞器中的蛋白质合成。
