Introduction. Empirical vancomycin (VAN) treatment failure for methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia, with significantly higher mortality, has been reported for MRSA strains with reduced VAN susceptibility. Aim. Our goal was to study the effect of sub-culture on VAN minimum inhibitory concentration (MIC) values compared to direct susceptibility of MRSA-positive blood cultures. Methodology. Using 19 MRSA-positive blood cultures and 19 seeded MRSA-positive blood cultures, we compared the VAN MICs from direct susceptibility testing of MRSA-positive blood cultures and MRSA sub-cultured from positive blood cultures. Results. In comparing direct VAN MICs from MRSA-positive blood cultures and standard agar dilution, nearly half of the MICs from agar dilution were lower, with one sample decreasing from 1.5 to 0.75 µg ml−1. Furthermore, in seeded blood cultures, 80 % or more showed lower values from standard agar dilution compared to direct VAN MICs. Conclusion. Our results reveal a trend towards lower MICs after positive blood culture isolates are sub-cultured. Some clinical failures among MRSA infections treated with VAN may result from this phenomenon.

中文翻译：

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阳性MRSA血液培养物的亚培养会影响万古霉素MIC吗？

引言。对于降低了VAN敏感性的MRSA菌株，已经报道了万古霉素（VAN）治疗耐甲氧西林金黄色葡萄球菌（MRSA）菌血症的经验失败，其死亡率明显更高。目的。我们的目标是研究与MRSA阳性血液培养的直接敏感性相比，传代培养对VAN最低抑菌浓度（MIC）值的影响。方法论。我们使用19种MRSA阳性血液培养物和19种接种的MRSA阳性血液培养物，比较了直接对MRSA阳性血液培养物进行敏感性测试的VAN MIC和从阳性血液培养物进行亚培养的MRSA。结果 。在比较来自MRSA阳性血液培养物和标准琼脂稀释液的直接VAN MICs时，来自琼脂稀释液的MICs几乎降低了一半，其中一个样品从1.5 µg ml -1降至0.75 µg ml -1。此外，在种子血液培养物中，与直接VAN MIC相比，标准琼脂稀释液中80％或更高的值显示出较低的值。结论。我们的结果揭示了将阳性血液培养分离株继代培养后，MIC降低的趋势。VAN处理的MRSA感染中某些临床失败可能是由这种现象引起的。