Cantón R, Mir N, Martínez-Ferrer M, Sánchez del Saz B, Soler I, Baquero F
Servicio de Microbiología, Hospital Ramón y Cajal, Madrid.
Rev Esp Quimioter. 1999 Mar;12(1):48-53.
The emergence of clinical methicillin-resistant Staphylococcus aureus with reduced susceptibility to glycopeptides has recently been documented. Heterogeneous levels of glycopeptides susceptibility have been demonstrated in these isolates. Prospectively, we investigated the presence of S. aureus isolates with reduced susceptibility to vancomycin in our hospital from October 1997 to January 1998. The vancomycin and teicoplanin susceptibility of 248 consecutively methicillin-susceptible and -resistant S. aureus isolates from clinical and surveillance specimens was studied by broth microdilution and agar dilution methods. In addition, 108 CFU/mI of overnight cultures were plated onto BHI-agar plates containing 6 and 10 microg/ml of vancomycin and were incubated for 48 hours at 35 degrees C. Under these conditions selected colonies were subcultured onto vancomycin plates and vancomycin susceptibility (E-test) was determined again. Vancomycin MIC(90) values by the agar dilution technique for methicillin-susceptible and -resistant isolates were 2 and 4 microg/ml, respectively No selected colonies were observed on 10 microg/ml vancomycin plates. In contrast, 12 isolates, including 8 (3.9%) methicillin-susceptible and 4 (9. 1%) methicillin-resistant isolates, showed subpopulations at a frequency rate of 10(-6)-10(-7) on 6 microg/ml vancomycin plates. Nevertheless, a significant increase in MIC values for vancomycin was not observed in these S. aureus subpopulations.
近期已有文献报道临床出现了对糖肽类药物敏感性降低的耐甲氧西林金黄色葡萄球菌。这些分离株对糖肽类药物的敏感性存在异质性水平。前瞻性地，我们调查了1997年10月至1998年1月我院对万古霉素敏感性降低的金黄色葡萄球菌分离株的情况。采用肉汤微量稀释法和琼脂稀释法研究了248株来自临床和监测标本的甲氧西林敏感及耐药金黄色葡萄球菌分离株对万古霉素和替考拉宁的敏感性。此外，将过夜培养物的108 CFU/ml接种到含6和10 μg/ml万古霉素的脑心浸液琼脂平板上，于35℃孵育48小时。在这些条件下，挑选出的菌落转种到万古霉素平板上，再次测定万古霉素敏感性（E试验）。琼脂稀释法测定的甲氧西林敏感和耐药分离株的万古霉素MIC(90)值分别为2和4 μg/ml。在含10 μg/ml万古霉素的平板上未观察到挑选出的菌落。相反，12株分离株，包括8株（3.9%）甲氧西林敏感株和4株（9.1%）甲氧西林耐药株，在含6 μg/ml万古霉素的平板上以10(-6)-10(-7)的频率出现亚群。然而，在这些金黄色葡萄球菌亚群中未观察到万古霉素MIC值的显著增加。
