Schnitzler N, Podbielski A, Baumgarten G, Mignon M, Kaufhold A
Institute of Medical Microbiology, Technical University RWTH Aachen, Germany.
J Clin Microbiol. 1995 Feb;33(2):356-63. doi: 10.1128/jcm.33.2.356-363.1995.
Many group G streptococci (GGS) isolated from infected humans (but not from animal sources) express M or M-like proteins with biological, immunochemical, and genetic features similar to those of group A streptococci (GAS). To further elucidate the recently proposed M-like protein gene (emmL gene) polymorphisms in GGS, Southern blots of genomic DNAs from 38 epidemiologically unrelated GGS strains isolated from human specimens and 12 GGS strains recovered from animal sources were hybridized with oligonucleotide probes designed to specifically detect GAS M class I and M class II M protein (emm) genes. All human-associated GGS strains showed DNA homology to the GAS M class I emm gene probe, whereas no hybridization was found with DNA from any of the animal-associated strains. The emmL genes from all human isolates were amplified by PCR, and the complete sequence of the emmL gene of the Rebecca Lancefield grouping strain D166B was determined. Again, this gene exhibited the structural features typical for emm genes of M class I GAS. The 5' regions of the PCR-amplified emmL genes of the remaining 37 human GGS strains were sequenced. This region showed a sequence diversity similar to that known for GAS emm genes. When strains whose N-terminal emmL gene sequences showed a homology of > 95% were defined as belonging to one genetic type, 30 strains were segregated into six distinct genetic types, whereas the remaining 8 strains each exhibited a unique emmL gene sequence. A high degree of homology between the N-terminal emmL gene segments of six GGS strains and the corresponding regions of either the emm12 or the emm57 gene of GAS was found, suggesting a horizontal gene transfer between strains of these species of beta-hemolytic streptococci. Besides a further understanding of the evolution of GGS emmL genes, the observed emmL gene polymorphisms in GGS could provide the basis for a molecular subspecies delineation of strains and offers the potential of typing GGS for epidemiological purposes.
许多从感染人类（而非动物源）中分离出的G群链球菌（GGS）表达的M或M样蛋白具有与A群链球菌（GAS）相似的生物学、免疫化学和遗传学特征。为了进一步阐明最近提出的GGS中M样蛋白基因（emmL基因）的多态性，用设计用于特异性检测GAS M I类和M II类M蛋白（emm）基因的寡核苷酸探针，对从人类标本中分离出的38株流行病学无关的GGS菌株和从动物源中分离出的12株GGS菌株的基因组DNA进行Southern杂交。所有与人类相关的GGS菌株均显示与GAS M I类emm基因探针具有DNA同源性，而未发现与任何动物相关菌株的DNA发生杂交。通过PCR扩增了所有人类分离株的emmL基因，并测定了Rebecca Lancefield分组菌株D166B的emmL基因的完整序列。同样，该基因表现出M I类GAS的emm基因典型的结构特征。对其余37株人类GGS菌株的PCR扩增emmL基因的5'区域进行了测序。该区域显示出与GAS emm基因已知的序列多样性相似。当N末端emmL基因序列同源性> 95%的菌株被定义为属于同一遗传类型时，30株菌株被分为六个不同的遗传类型，而其余8株菌株各自表现出独特的emmL基因序列。发现六株GGS菌株的N末端emmL基因片段与GAS的emm12或emm57基因的相应区域之间具有高度同源性，表明在这些β溶血性链球菌菌株之间发生了水平基因转移。除了进一步了解GGS emmL基因的进化外，在GGS中观察到的emmL基因多态性可为菌株的分子亚种划分提供基础，并为流行病学目的对GGS进行分型提供了潜力。
