万古霉素耐药折点调整对异质性万古霉素中介金黄色葡萄球菌筛选方法的影响

Effect of updating vancomycin breakpoint for resistant Staphylococcus aureus on plate screening of hetero-resistant vancomycin intermediate Staphylococcus aureus

目的探讨耐甲氧西林金黄色葡萄球菌(金葡菌)(MRSA)对万古霉素耐药的折点调整后,对异质性万古霉素中介金葡菌(h VISA)的平皿筛选方法选择的影响,寻求一种敏感、有效的平皿筛选方法。方法收集临床MRSA菌株215株,分别用浓度为6 mg/L、4 mg/L、2 mg/L万古霉素脑心浸液琼脂平皿(BHIV6、BHIV4、BHIV2)及浓度为5 mg/L替考拉宁脑心浸液琼脂(BHIT5)进行h VISA筛选,同时应用菌群分析/曲线下面积(PAP/AUC)法检测h VISA,以PAP/AUC法作为金标准,对比上述4种平皿筛选方法的敏感度及特异度。结果 PAP/AUC检测h VISA的阳性菌株分别为12株,BHIV6、BHIV4、BHIV2、BHIT5筛选阳性菌株分别为6、18、54、20株;以PAP/AUC法作为金标准,上述4种平皿筛选方法灵敏度分别为41.7%、83.3%、91.7%、83.3%,特异度分别为99.0%、95.9%、77.8%、94.8%。结论 MRSA对万古霉素耐药折点调整后,BHIV6筛选法灵敏度较低、BHIV2筛选法特异度较低,不应作为h VISA的筛选方法,BHIV4和BHIT5平皿筛选法灵敏度和特异度均较高,可作为万古霉素耐药折点调整后对h VISA的常规筛选方法。

Abstract： Objective To examine the effect of updating vancomycin breakpoints for resistant Staphylococcus aureus on plate screening of hetero-resistant vancomycin intermediate Staphylococcus aureus （hVISA） to find a sensitive and effective plate screening method for detecting hVISA isolates. Methods Atotal of 215 clinical isolates ofmethicillin-resistant Staphylococcus aureus （MRSA） were collected. The hVISA isolates were identified on the brain heart infusion agar screening plates containing 6 mg/L vancomycin （BHIV6）, 4 mg/L vancomycin （BHIV4）, 2 mg/L vancomycin （BHIV2） and 5 mg/L teicoplanin （BHIT5）, respectively. Meanwhile, we also detected hVISA by the population analysis profile/area under the curve （PAP/AUC） method. The PAP/AUC method was taken as the gold standard. We calculated the sensitivity and specificity of BHIV6, BHIV4, BHIV2, BHIT5 screening methods as compared with PAP/AUC method. Results PAP/AUC method identified 12 hVISA strains from the MRSA. BHIV6, BHIV4, BHIV2, and BHIT5 plate screening methods identified 6, 18, 54, 20 hVISA strains, respectively. The sensitivity of these four screening methods was 41.7 %, 83.3 %, 91.7 %, and 83.3 %, respectively. The corresponding specificity of these methods was 99.0 %, 95.9 %, 77.8 %, and 94.8 %, respectively. Conclusions After the vancomycin breakpoint for resistant S. aureus is updated, BHIV6 and BHIV2 screening methods are not so valid for detecting hVISA due tolower sensitivity or specificity. BHIV4 and BHIT5 screening methods are still valid for identifying hVISA strains with higher sensitivity and specificity.