Howden Benjamin P, Johnson Paul D R, Ward Peter B, Stinear Timothy P, Davies John K
Department of Microbiology, Monash University, Clayton, 3800 Victoria, Australia.
Antimicrob Agents Chemother. 2006 Sep;50(9):3039-47. doi: 10.1128/AAC.00422-06.
Low-level vancomycin-resistant Staphylococcus aureus (vancomycin-intermediate S. aureus [VISA] and heterogenous VISA [hVISA]) is increasingly reported and leads to glycopeptide treatment failure. Various phenotypic features have been reported for these isolates, but the genetic changes leading to hVISA and VISA have yet to be clearly determined. We assessed phenotypic, antibiotic resistance, and genomic changes by using genomic DNA microarray comparison and sequencing of selected loci in five pairs of clinical hVISA/VISA strains and the initial methicillin-resistant Staphylococcus aureus (MRSA) isolates obtained prior to vancomycin therapy. The isolates were from adult patients in Australia and New Zealand who had persistent MRSA bacteremia (>7 days) while receiving vancomycin therapy. In all cases, the initial isolates were found to be fully vancomycin-susceptible Staphylococcus aureus (VSSA). The hVISA/VISA phenotype was associated with increased cell wall thickness, reduced autolytic activity in four of five hVISA/VISA strains, and a striking reduction in biofilm formation compared to the parent strains in all pairs. All five pairs appeared to be isogenic, and genomic DNA microarray comparison suggested that major genetic changes are not required for the development of the resistant phenotype in these strains. No sequence differences were found in the agr locus or the tcaRA genes for any pair, but a marked reduction in RNAIII expression was found in four pairs. In summary, hVISA/VISA arises from fully VSSA during persistent infection that fails to respond to glycopeptide therapy and is associated with significant phenotypic changes, including a marked reduction in biofilm-forming ability. These clinically derived pairs of isolates will be a useful resource to elucidate the genetic mechanism of resistance in hVISA/VISA strains.
低水平耐万古霉素金黄色葡萄球菌（万古霉素中介金黄色葡萄球菌[VISA]和异质性VISA[hVISA]）的报道日益增多，并导致糖肽类治疗失败。已报道了这些菌株的各种表型特征，但导致hVISA和VISA的基因变化尚未明确确定。我们通过基因组DNA微阵列比较以及对五对临床hVISA/VISA菌株和万古霉素治疗前获得的初始耐甲氧西林金黄色葡萄球菌（MRSA）分离株的选定基因座进行测序，评估了表型、抗生素耐药性和基因组变化。这些分离株来自澳大利亚和新西兰的成年患者，他们在接受万古霉素治疗期间持续存在MRSA菌血症（>7天）。在所有病例中，初始分离株均被发现为对万古霉素完全敏感的金黄色葡萄球菌（VSSA）。与亲本菌株相比，hVISA/VISA表型与细胞壁厚度增加、五株hVISA/VISA菌株中有四株的自溶活性降低以及生物膜形成显著减少有关。所有五对菌株似乎都是同基因的，基因组DNA微阵列比较表明，这些菌株耐药表型的发展不需要主要的基因变化。任何一对菌株在agr基因座或tcaRA基因中均未发现序列差异，但四对菌株中发现RNAIII表达显著降低。总之，hVISA/VISA在持续感染期间由完全VSSA产生，对糖肽类治疗无反应，并与显著的表型变化有关，包括生物膜形成能力显著降低。这些临床来源的菌株对将是阐明hVISA/VISA菌株耐药遗传机制的有用资源。
