Department of Internal Medicine, E-Da Hospital/I-Shou University, Kaohsiung, Taiwan.
BMC Infect Dis. 2010 Jun 7;10:159. doi: 10.1186/1471-2334-10-159.
Previous studies regarding the prognosis of patients infected with MRSA isolates characterized by a high minimum inhibitory concentration (MIC) for vancomycin have generally used a commercial Etest. Little research has been conducted on determining the vancomycin susceptibility of MRSA using a reference microdilution. Additionally, there is discordance between the MIC result from an Etest and the value determined using the reference microdilution method.
Using a reference microdilution method, we determined the MIC of vancomycin for isolates from 123 consecutive patients with nosocomial MRSA bacteremia. The clinical features and outcome for these patients were recorded and the MRSA isolates were genotyped.
Among the 123 non-duplicated isolates, 21.1% had a MIC = 2 mg/L, 76.4% had a MIC = 1 mg/L and 2.4% had MIC = 0.5 mg/L. Patients with MRSA bacteremia in the ICU or those who had been hospitalized for a long time were more likely to be infected with strains of high vancomycin MIC MRSA (MIC = 2 mg/L; p < 0.05). Cox regression analysis demonstrated that the high MIC group had a significantly higher 30-day mortality than the low MIC group (HR: 2.39; 95% CI: 1.20-4.79; p = 0.014). Multivariate analyses indicated that the presence of high MIC isolates, pneumonia, post-cardiothoracic surgery and a high Charlson comorbidity index were all independent predictors of a 30-day mortality. Genotyping of these high vancomycin MIC isolates demonstrated that SCCmec III, spa type037, was the predominant strain (> 80%). The rates of resistance to trimethoprim/sulfamethoxazole, gentamicin, levofloxacin, rifampin and tetracycline were also higher in the high MIC group than in the isolates belonging to low MIC group (p < 0.05).
In a high vancomycin MIC group in Taiwan, SCCmec III, spa type t037, was the predominant strain of MRSA identified. Patients with MRSA bacteremia in the ICU or who had prolonged hospitalization were more likely to be infected with S. aureus strains with high vancomycin MICs. The mortality rate was higher among patients infected with these strains compared to patients infected with low MIC strains.
先前关于耐万古霉素高最低抑菌浓度（MIC）的金黄色葡萄球菌（MRSA）分离株患者预后的研究，通常使用商业 Etest 进行。使用参考微量稀释法来确定 MRSA 的万古霉素药敏性的研究较少。此外，Etest 的 MIC 结果与参考微量稀释法测定的值之间存在差异。
使用参考微量稀释法，我们确定了 123 例连续住院的耐万古霉素金黄色葡萄球菌菌血症患者的万古霉素 MIC。记录这些患者的临床特征和结局，并对 MRSA 分离株进行基因分型。
在 123 个非重复分离株中，21.1%的 MIC=2mg/L，76.4%的 MIC=1mg/L，2.4%的 MIC=0.5mg/L。在 ICU 住院或住院时间较长的耐万古霉素金黄色葡萄球菌菌血症患者更有可能感染高万古霉素 MIC 的耐万古霉素金黄色葡萄球菌（MIC=2mg/L；p<0.05）。Cox 回归分析表明，高 MIC 组 30 天死亡率明显高于低 MIC 组（HR：2.39；95%CI：1.20-4.79；p=0.014）。多变量分析表明，高 MIC 分离株、肺炎、心胸手术后和高 Charlson 合并症指数是 30 天死亡率的独立预测因素。对这些高万古霉素 MIC 分离株进行基因分型表明，SCCmec III、spa 型 t037 是主要流行株（>80%）。高 MIC 组对 trimethoprim/sulfamethoxazole、庆大霉素、左氧氟沙星、利福平、四环素的耐药率也高于低 MIC 组（p<0.05）。
在台湾的高万古霉素 MIC 组中，SCCmec III、spa 型 t037 是鉴定出的主要耐万古霉素金黄色葡萄球菌流行株。在 ICU 住院或住院时间较长的耐万古霉素金黄色葡萄球菌菌血症患者更有可能感染万古霉素 MIC 较高的金黄色葡萄球菌。与感染低 MIC 株的患者相比，感染这些菌株的患者死亡率更高。
