Department of Medicine, St. John Hospital and Medical Center, Detroit, Michigan, USA.
J Clin Microbiol. 2011 Jun;49(6):2147-50. doi: 10.1128/JCM.01435-10. Epub 2011 Apr 13.
Detection of Staphylococcus aureus isolates with intermediate vancomycin susceptibility (VISA) and heteroresistance (hVISA) remains problematic. The population analysis profile/area under the curve (PAP/AUC) is the gold standard but is cumbersome. We compared the performance of two Etest screening methods (macromethod [MAC] and glycopeptide resistance detection [GRD]) plus brain heart infusion (BHI) agars supplemented with 3 (BHI-V3) or 4 (BHI-V4) mg/liter vancomycin in detecting hVISA and/or VISA phenotypes. Etest hVISA screenings were done in parallel for 485 saved methicillin-resistant S. aureus (MRSA) blood isolates according to the manufacturer's instructions. The PAP/AUC was measured for all isolates according to the modified method. PAP/AUC test isolate/Mu3 ratios of <0.9, 0.9 to 1.3, and >1.3 were considered positive for susceptible MRSA (S-MRSA), hVISA, and VISA, respectively. PAP/AUC revealed seven VISA and 33 hVISA phenotypes. MAC screening was positive for 30 (75.0%) hVISA/VISA and 49 (11.0%) S-MRSA isolates. GRD screening was positive for 28 (70.0%) hVISA/VISA and 63 (14.2%) S-MRSA isolates. Growth on BHI-V3 was noted in all hVISA/VISA and 24 (5.4%) S-MRSA isolates. Growth on BHI-V4 was noted in all VISA and four (12.1%) hVISA isolates. None of the S-MRSA isolates grew on BHI-V4 agar. The sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values were 75.0%, 89.0%, 38.0%, and 97.5% for MAC; 70.0%, 85.8%, 30.8%, and 97.0% for GRD; 100%, 94.6%, 62.5%, and 100% for BHI-V3; and 100, 99.2%, 63.6%, and 100% for BHI-V4 (for detecting VISA). These findings suggest that both Etest screening methods have excellent NPV, but positive results require confirmation. BHI-V3 and BHI-V4 agars provide more precise identification of hVISA and VISA, respectively; they may be reasonable alternatives to PAP/AUC.
检测具有中间万古霉素敏感性（VISA）和异质耐药性（hVISA）的金黄色葡萄球菌分离株仍然存在问题。人群分析谱/曲线下面积（PAP/AUC）是金标准，但很繁琐。我们比较了两种 Etest 筛选方法（宏方法[MAC]和糖肽耐药检测[GRD]）以及添加 3（BHI-V3）或 4（BHI-V4）mg/L 万古霉素的脑心浸液（BHI）琼脂在检测 hVISA 和/或 VISA 表型方面的性能。根据制造商的说明，对 485 株保存的耐甲氧西林金黄色葡萄球菌（MRSA）血分离株平行进行 Etest hVISA 筛选。根据改良方法测量所有分离株的 PAP/AUC。PAP/AUC 测试分离株/Mu3 比值 <0.9、0.9 至 1.3 和 >1.3 分别被认为是敏感 MRSA（S-MRSA）、hVISA 和 VISA 的阳性。PAP/AUC 显示了七种 VISA 和 33 种 hVISA 表型。MAC 筛选对 30（75.0%）hVISA/VISA 和 49（11.0%）S-MRSA 分离株呈阳性。GRD 筛选对 28（70.0%）hVISA/VISA 和 63（14.2%）S-MRSA 分离株呈阳性。所有 hVISA/VISA 和 24（5.4%）S-MRSA 分离株均在 BHI-V3 上生长。所有 VISA 和 4 个（12.1%）hVISA 分离株均在 BHI-V4 琼脂上生长。没有 S-MRSA 分离株在 BHI-V4 琼脂上生长。MAC 的灵敏度、特异性和阳性（PPV）和阴性（NPV）预测值分别为 75.0%、89.0%、38.0%和 97.5%；GRD 为 70.0%、85.8%、30.8%和 97.0%；BHI-V3 为 100%、94.6%、62.5%和 100%；BHI-V4 为 100%、99.2%、63.6%和 100%（用于检测 VISA）。这些发现表明，两种 Etest 筛选方法均具有出色的 NPV，但阳性结果需要确认。BHI-V3 和 BHI-V4 琼脂分别更准确地鉴定了 hVISA 和 VISA；它们可能是 PAP/AUC 的合理替代方法。
