Laboratory for Antimicrobial Pharmacodynamics, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, State University of New York, New York, USA.
BMC Infect Dis. 2011 Oct 25;11:287. doi: 10.1186/1471-2334-11-287.
The development of hVISA has been associated with vancomycin clinical failures and is commonly misidentified in clinical microbiology laboratories. Therefore, the objectives of this present study was to improve the reliability of methodologies and criteria for identifying hVISA, evaluate the prevalence of hVISA among clinical bloodstream isolates of S. aureus and determine if there exists a relationship between accessory gene regulator (agr) dysfunction and the hVISA phenotype.
The presence of hVISA in 220 clinical S. aureus isolates (121 MSSA, 99 MRSA) from bloodstream infections was examined by CLSI broth microdilution, Macro & Standard Etest. Isolates which were classified as hVISA by Macro Etest, were additionally evaluated using a modified PAP-AUC method using a modified starting inoculum of 10(10) CFU/mL, and growth on brain heart infusion agar with 4 mg/L vancomycin (BHIV4) at 10(8) and 10(10) CFU/mL, and agr function was assessed by delta-hemolysin production.
Broth microdilution MIC(50/90) of S.aureus and hVISA was 1.0/2.0 and 1.5/2.0 mg/L (p= 0.02), respectively. Macro Etest identified 12 (5.5%) hVISA isolates; higher among MRSA (9.1%) versus MSSA (2.5%) (p = 0.03). The mean modified PAP-AUC ratios (> 0.8) of 7 MRSA strains and 3 MSSA strains were significantly different (p = 0.001). 58% of hVISA strains were found to be agr dysfunctional when 21% of MRSA strains were agr dysfunctional. hVISA was detected among S. aureus bloodstream isolates, which were classified as susceptible among clinical microbiology laboratories.
Evaluating the correlation between Etest MICs and modified PAP-AUC ratio values will add further improvement of discriminating hVISA, and agr dysfunction may be predictive of strains which display a greater predilection to display the hVISA phenotype.
hVISA 的出现与万古霉素临床治疗失败有关，且常被临床微生物学实验室误诊。因此，本研究旨在提高鉴定 hVISA 的方法学和标准的可靠性，评估金黄色葡萄球菌血流感染临床分离株中 hVISA 的流行率，并确定辅助基因调节（agr）功能障碍与 hVISA 表型之间是否存在关系。
采用 CLSI 肉汤微量稀释法和 Macro & Standard Etest 检测 220 株来自血流感染的临床金黄色葡萄球菌分离株（121 株 MSSA、99 株 MRSA）中 hVISA 的存在情况。Macro Etest 鉴定为 hVISA 的分离株，通过改良 PAP-AUC 法进一步评估，采用 10(10) CFU/mL 的起始接种量，在含 4mg/L 万古霉素的脑心浸液琼脂（BHIV4）上于 10(8) 和 10(10) CFU/mL 处生长，并通过 δ-溶血素产生评估 agr 功能。
金黄色葡萄球菌和 hVISA 的肉汤微量稀释 MIC(50/90)分别为 1.0/2.0 和 1.5/2.0mg/L（p=0.02）。Macro Etest 鉴定出 12 株（5.5%）hVISA 分离株；MRSA 中检出率更高（9.1%），而非 MSSA（2.5%）（p=0.03）。7 株 MRSA 株和 3 株 MSSA 株的改良 PAP-AUC 比值（>0.8）均值差异显著（p=0.001）。21%的 MRSA 株存在 agr 功能障碍，而 58%的 hVISA 株存在 agr 功能障碍。在临床微生物学实验室分类为敏感的金黄色葡萄球菌血流分离株中检测到 hVISA。
评估 Etest MIC 与改良 PAP-AUC 比值之间的相关性，将进一步提高鉴定 hVISA 的能力，agr 功能障碍可能预示着更容易出现 hVISA 表型的菌株。
