Ramaswamy Srinivas V, Ferrieri Patricia, Madoff Lawrence C, Flores Aurea E, Kumar Nikhil, Tettelin Hervé, Paoletti Lawrence C
Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Departments of Laboratory Medicine and Pathology and Pediatrics, University of Minnesota Medical School, Minneapolis, MN 55455, USA.
J Med Microbiol. 2006 Jun;55(Pt 6):775-783. doi: 10.1099/jmm.0.46253-0.
Group B Streptococcus (GBS) is an important pathogen responsible for a variety of diseases in newborns and the elderly. A clinical GBS isolate is considered nontypable (NT) when serological methods fail to identify it as one of nine known GBS serotypes. Eight clinical isolates (designated A1-A4, B1-B4) showed PFGE profiles similar to that of a GBS serotype V strain expressing R1, R4 surface proteins. These unique isolates were further characterized by immunologic and genetic methods. Rabbit sera to isolates A1 and A2 reacted weakly with concentrated HCl extracts of A1-A4 isolates, but not with those of B1-B4 isolates. In addition, a type V capsular polysaccharide (CPS) inhibition ELISA revealed that cell wall extracts from isolates A1-A4, but not from B1-B4, expressed low but measurable amounts of type V CPS. Molecular serotyping with PCR analysis showed that all eight isolates contained a type V-specific CPS gene (cpsO) and harboured the gene encoding the surface protein Alp3. Multilocus sequence typing identified isolate A1 as belonging to a new sequence type (ST) designated ST-173, whereas the other seven isolates keyed to ST-1. Sequencing of the 18 genes (17 736 bp) in the cps locus showed that each NT isolate harboured one to three unique polymorphisms, and also identified an IS1381 element in cpsE of the B4 isolate. Collectively, genetic and immunologic analyses revealed that these NT isolates expressing R1, R4 proteins have a genetic profile consistent with that of type V, an emergent, antigenically diverse and increasingly prevalent GBS serotype.
B族链球菌（GBS）是导致新生儿和老年人多种疾病的重要病原体。当血清学方法无法将临床GBS分离株鉴定为已知的9种GBS血清型之一时，该分离株被认为是不可分型（NT）的。8株临床分离株（命名为A1 - A4、B1 - B4）的脉冲场凝胶电泳（PFGE）图谱与表达R1、R4表面蛋白的GBS血清型V菌株相似。通过免疫学和遗传学方法对这些独特的分离株进行了进一步表征。针对分离株A1和A2的兔血清与A1 - A4分离株的浓盐酸提取物反应较弱，但与B1 - B4分离株的提取物无反应。此外，V型荚膜多糖（CPS）抑制ELISA显示，A1 - A4分离株的细胞壁提取物表达了少量但可测量的V型CPS，而B1 - B4分离株则未表达。PCR分析的分子血清学分型显示，所有8株分离株都含有V型特异性CPS基因（cpsO），并携带编码表面蛋白Alp3的基因。多位点序列分型确定分离株A1属于一个新的序列型（ST），命名为ST - 173，而其他7株分离株归为ST - 1。对cps位点的18个基因（17 736 bp）进行测序表明，每个NT分离株都有1至3个独特的多态性，并且在B4分离株的cpsE中鉴定出一个IS1381元件。总体而言，遗传学和免疫学分析表明，这些表达R1、R4蛋白的NT分离株具有与V型一致的遗传特征，V型是一种新出现的、抗原性多样且日益普遍的GBS血清型。
