Chua Thea, Moore Carol L, Perri Mary B, Donabedian Susan M, Masch William, Vager Dora, Davis Susan L, Lulek Kaitlin, Zimnicki Benjamin, Zervos Marcus J
Henry Ford Health System, Wayne State University School of Medicine, Detroit, Michigan 48202, USA.
J Clin Microbiol. 2008 Jul;46(7):2345-52. doi: 10.1128/JCM.00154-08. Epub 2008 May 28.
To gain a better understanding of epidemiology of resistance in Staphylococcus aureus, we describe the molecular epidemiology of methicillin-resistant Staphylococcus aureus bloodstream isolates in urban Detroit. Bloodstream isolates from July 2005 to February 2007 were characterized. Two hundred ten bloodstream isolates from 201 patients were evaluated. Patient characteristics were as follows: median age, 54 years; 56% male; and 71% African-American. Seventy-six percent of infections were health care associated, with 55% being community-onset infections and 21% hospital acquired, and 24% were community associated. The most common sources were skin/wound (25%), central venous catheters (24%), unknown source (20%), and endocarditis (9%). Ninety percent and 5% of isolates had a MIC of vancomycin of <or=1.0 mg/liter, using automated dilution testing and E-test, respectively. Six percent of isolates showed heteroresistance to vancomycin, all occurring with isolates having a vancomycin E-test MIC of >or=1.5 mg/liter. Results of pulsed-field gel electrophoresis showed 17 strain types. The predominant strains were USA100 (104 isolates) and USA300 (74 isolates). Forty-nine percent of the isolates had staphylococcal cassette chromosome mec II, and 56% had agr II. All USA300 isolates were positive for the Panton-Valentine leukocidin toxin genes and agr I. Forty-seven percent of USA300 bloodstream infections were health care associated (35% community onset and 12% hospital onset). USA300 strains were more common in injection drug users with skin/wound as the predominant source of infection. Thirty percent of the USA100 strains were closely related to vancomycin-resistant Staphylococcus aureus isolates. The results of this study show that vancomycin MICs using automated dilution testing with Vitek-2 and E-test were highly discordant. Most methicillin-resistant S. aureus strains causing bacteremia are health care associated, commonly have MICs of vancomycin that are high within the susceptible range are not detected by routine automated dilution testing, and have significant diversity of molecular characteristics. USA100 strains that are closely related to vancomycin-resistant S. aureus (VRSA) isolates and USA300 strains are common as causes of both hospital and community-onset infection. Infection control measures should focus not only on prevention of the spread of community strains in the hospital but also prevention of the spread of hospital strains associated with VRSA into the community.
为了更好地了解金黄色葡萄球菌耐药性的流行病学情况，我们描述了底特律市区耐甲氧西林金黄色葡萄球菌血流感染分离株的分子流行病学特征。对2005年7月至2007年2月期间的血流感染分离株进行了特征分析。对来自201例患者的210株血流感染分离株进行了评估。患者特征如下：年龄中位数为54岁；男性占56%；非裔美国人占71%。76%的感染与医疗保健相关，其中55%为社区起病感染，21%为医院获得性感染，24%为社区相关性感染。最常见的感染源是皮肤/伤口（25%）、中心静脉导管（24%）、不明来源（20%）和心内膜炎（9%）。分别使用自动稀释试验和E试验时，90%和5%的分离株万古霉素最低抑菌浓度（MIC）≤1.0mg/L。6%的分离株对万古霉素表现出异质性耐药，均发生在万古霉素E试验MIC≥1.5mg/L的分离株中。脉冲场凝胶电泳结果显示有17种菌株类型。主要菌株为USA100（104株）和USA300（74株）。49%的分离株含有葡萄球菌盒式染色体mec II，56%含有agr II。所有USA300分离株的杀白细胞素毒素基因和agr I均呈阳性。47%的USA300血流感染与医疗保健相关（35%为社区起病，12%为医院起病）。USA300菌株在以皮肤/伤口为主要感染源的注射吸毒者中更为常见。30%的USA100菌株与耐万古霉素金黄色葡萄球菌分离株密切相关。本研究结果表明，使用Vitek-2自动稀释试验和E试验测得的万古霉素MIC差异很大。大多数引起菌血症的耐甲氧西林金黄色葡萄球菌菌株与医疗保健相关，通常万古霉素MIC在敏感范围内较高，常规自动稀释试验无法检测到，且分子特征具有显著多样性。与耐万古霉素金黄色葡萄球菌（VRSA）分离株密切相关的USA100菌株和USA300菌株是医院和社区起病感染的常见病因。感染控制措施不仅应侧重于预防社区菌株在医院内传播，还应预防与VRSA相关的医院菌株传播到社区。
