Klepser M E, Ernst E J, Ernst M E, Messer S A, Pfaller M A
College of Pharmacy, University of Iowa, Iowa City 52242, USA.
Antimicrob Agents Chemother. 1998 Jun;42(6):1387-91. doi: 10.1128/AAC.42.6.1387.
We have previously reported poor correlation between the in vitro fungicidal activity of LY303366 and MIC results in RPMI medium based upon the manufacturer's suggested susceptibility endpoint, lack of visual growth. Additionally, we have noted a significant trailing effect with LY303366 when MICs are determined in RPMI medium. These observations have led us to evaluate an alternative susceptibility endpoint for LY303366, an 80% reduction in growth compared with control (similar to that utilized for azoles). Two isolates each of Candida albicans, Candida glabrata, and Candida tropicalis were selected for testing. MICs were determined for LY303366 in RPMI 1640 medium buffered with morpholinepropanesulfonic acid. MICs were determined with suggested (MIC100) and experimental (MIC80) endpoints. The minimal fungicidal concentration (MFC) of LY303366 for each isolate was also determined. Time-kill curves were determined in RPMI medium with each isolate at concentrations of LY303366 ranging from 0.125 to 16x MIC80 to assess the correlation between MIC80 and fungicidal activity. Lastly, fungi exposed to LY303366 were examined via scanning electron microscope (SEM) for evidence of drug-induced ultrastructure change. MIC80s for test isolates ranged from 0.015 to 0.12 microgram/ml and were consistently three to five wells less than MIC100s. Good correlation was observed between fungicidal activity, as assessed by kill curves, and the MIC80. SEM data revealed significant ultrastructure changes induced by LY303366 even at sub-MIC80s. Based on our results demonstrating better correlation between MIC80 and fungicidal activity, i.e., time-kill curves and MFCs, we suggest that 80% reduction in visible growth be utilized as the endpoint for susceptibility determinations with LY303366 in RPMI medium.
我们之前曾报道，基于制造商建议的药敏终点（即无可见生长），LY303366在RPMI培养基中的体外杀真菌活性与MIC结果之间的相关性较差。此外，我们还注意到，当在RPMI培养基中测定MIC时，LY303366存在显著的拖尾效应。这些观察结果促使我们评估LY303366的另一种药敏终点，即与对照相比生长减少80%（类似于用于唑类药物的终点）。选择白色念珠菌、光滑念珠菌和热带念珠菌各两株进行测试。在以吗啉丙磺酸缓冲的RPMI 1640培养基中测定LY303366的MIC。分别按照建议的终点（MIC100）和实验终点（MIC80）测定MIC。还测定了LY303366对各分离株的最低杀菌浓度（MFC）。在RPMI培养基中，用LY303366浓度范围为0.125至16倍MIC80的各分离株测定时间杀菌曲线，以评估MIC80与杀真菌活性之间的相关性。最后，通过扫描电子显微镜（SEM）检查暴露于LY303366的真菌，以寻找药物诱导超微结构变化的证据。测试分离株的MIC80范围为0.015至0.12微克/毫升，始终比MIC100少三到五个孔。通过杀菌曲线评估的杀真菌活性与MIC80之间观察到良好的相关性。SEM数据显示，即使在低于MIC80的浓度下，LY303366也会引起显著的超微结构变化。基于我们的结果表明MIC80与杀真菌活性（即时间杀菌曲线和MFC）之间具有更好的相关性，我们建议将可见生长减少80%用作在RPMI培养基中测定LY303366药敏性的终点。
