Optimer Pharmaceuticals, Inc., 4755 Nexus Center Drive, San Diego, CA 92121, USA.
J Antimicrob Chemother. 2013 Mar;68(3):515-22. doi: 10.1093/jac/dks450. Epub 2012 Dec 2.
Fidaxomicin, which was recently approved for the treatment of Clostridium difficile-associated diarrhoea, demonstrates narrow-spectrum bactericidal activity via inhibition of RNA polymerase. In this study we evaluated its inhibitory activity versus C. difficile toxin gene expression and toxin production by quantifying toxin mRNA and protein.
The effects of fidaxomicin, its major metabolite (OP-1118), vancomycin and metronidazole on toxin A and toxin B production were determined by assaying culture supernatants of two C. difficile isolates (ATCC 43255, a high-level toxin-producing strain, and UK-14, a NAP1/027/BI epidemic strain) using a commercial ELISA. The effects of the drugs on toxin gene expression were assessed in stationary-phase cells of C. difficile strain UK-1 (NAP1/027/BI type epidemic strain) and in the closely related non-epidemic strain CD196 by quantitative RT-PCR.
Subinhibitory levels (1/4× MIC) of fidaxomicin or OP-1118 (but not vancomycin or metronidazole) strongly suppressed toxin production in C. difficile (≥ 60%) through at least 1 week of culture. Additionally, transcripts from the pathogenicity loci (tcdR, tcdA and tcdB) were nearly completely inhibited by both fidaxomicin (2× MIC) and OP-1118 (2.5× MIC), but not vancomycin (2.5× MIC).
Both fidaxomicin and OP-1118 are able to inhibit toxin production in vitro, which may explain prior post-treatment observations of less frequent detectable toxin in fidaxomicin-treated patients (27 subjects) than those treated with vancomycin (8 patients).
利福昔明最近被批准用于治疗艰难梭菌相关性腹泻,它通过抑制 RNA 聚合酶发挥窄谱杀菌活性。在这项研究中,我们通过定量检测毒素 mRNA 和蛋白来评估其对艰难梭菌毒素基因表达和毒素产生的抑制活性。
采用商业 ELISA 法检测两种艰难梭菌分离株(ATCC 43255,高水平产毒株和 UK-14,NAP1/027/BI 流行株)培养上清液中毒素 A 和毒素 B 的产生,评估利福昔明、其主要代谢物(OP-1118)、万古霉素和甲硝唑对毒素产生的影响。采用定量 RT-PCR 评估药物对艰难梭菌 UK-1 株(NAP1/027/BI 流行株)和密切相关的非流行株 CD196 中菌株的毒素基因表达的影响。
亚抑菌浓度(1/4×MIC)的利福昔明或 OP-1118(而非万古霉素或甲硝唑)通过至少 1 周的培养强烈抑制艰难梭菌的毒素产生(≥60%)。此外,致病性基因座(tcdR、tcdA 和 tcdB)的转录本几乎完全被利福昔明(2×MIC)和 OP-1118(2.5×MIC)抑制,但万古霉素(2.5×MIC)不能抑制。
利福昔明和 OP-1118 均可抑制体外毒素产生,这可能解释了利福昔明治疗组(27 例患者)较万古霉素治疗组(8 例患者)治疗后毒素检测频率较低的既往治疗后观察结果。