Cleary P P, McLandsborough L, Ikeda L, Cue D, Krawczak J, Lam H
Department of Microbiology, University of Minnesota, Minneapolis 55126, USA.
Mol Microbiol. 1998 Apr;28(1):157-67. doi: 10.1046/j.1365-2958.1998.00786.x.
A clonal variant of serotype M1 group A streptococcus, strain 90-131, disseminated to several continents, where it was associated with severe systemic infections and toxic shock. Although this strain harbours the speA gene and is efficiently internalized by human epithelial cells, clinical isolates often fail to express the erythrogenic toxin under laboratory growth conditions. Cultures of strain 90-131 were observed to phase vary between small, dry, compact and larger, more mucoid colonies. The former were shown to be poorly internalized by epithelial cells. Analysis of RNA by Northern hybridization demonstrated that the emml, hasA and speA genes were weakly transcribed in cultures derived from the small colonies and highly transcribed in those derived from the large colonies. An insertion mutation in mga (the multigene activator) downregulated the invasion of epithelial cells and the transcription of emm1 and hasA, but had little impact on the transcription of speA. These are the first data to suggest the existence of a common regulatory circuit linking intracellular invasion, M protein, hyaluronic acid capsule and erythrogenic toxin expression by group A streptococcus. Moreover, the genetic instability of toxin expression exhibited by this serotype may impact on laboratory studies that attempt to associate toxin production with toxic shock.
A群链球菌M1血清型的一个克隆变体菌株90 - 131传播到了几个大洲，在那里它与严重的全身感染和中毒性休克有关。尽管该菌株携带speA基因并能被人上皮细胞有效内化，但临床分离株在实验室培养条件下往往无法表达致热毒素。观察到90 - 131菌株的培养物在小的、干燥的、紧密的菌落和较大的、更黏液样的菌落之间发生相变。结果表明，前者被上皮细胞内化的能力较差。通过Northern杂交分析RNA表明，emm1、hasA和speA基因在源自小菌落的培养物中弱转录，而在源自大菌落的培养物中高转录。mga（多基因激活剂）中的插入突变下调了上皮细胞的侵袭以及emm1和hasA的转录，但对speA的转录影响很小。这些是首批表明存在一个共同调控回路的数据，该回路将A群链球菌的细胞内侵袭、M蛋白、透明质酸荚膜和致热毒素表达联系起来。此外，该血清型所表现出的毒素表达的遗传不稳定性可能会影响试图将毒素产生与中毒性休克相关联的实验室研究。
