Azoulay-Dupuis E, Rieux V, Rivier C, Trombe M C
INSERM U13, Hôpital Bichat, Paris, France.
Res Microbiol. 1998 Jan;149(1):5-13. doi: 10.1016/s0923-2508(97)83618-2.
Streptococcus pneumoniae is a pathogen in which the extracellular calcium concentration plays a major physiological role, in growth as well as in the induction of competence for genetic transformation and activation of autolysis. Both responses are under the control of a protein activator exported in the medium. We have checked the impact of mutations which alter the regulation of competence and autolysis on experimental virulence. Isogenic encapsulated derivatives carrying the relevant mutations were serotype 3 smooth clones, obtained by transformation of the relevant rough strains with DNA from a serotype 3 smooth isolate. Survival kinetics and bacterial clearance from the blood were followed after intraperitoneal infection of Swiss mice with the different bacterial cultures. In this model, mutants showing an attenuation of virulence relative to the wild type fell into two classes. In the first, represented by the lytA::ery mutant V1095 defective for calcium-induced autolysis, attenuated virulence could be correlated with rapid bacterial clearance from the blood. In the second, represented by the dmb mutants V2200 and V3300, attenuation was associated with delayed bacterial clearance from the blood, and correlated with altered kinetics of calcium transport and of regulation of competence and autolysis. It appeared unlikely that attenuation of virulence for strains V2200 and V3300 was a direct consequence of their competence phenotype, since the com::ery mutants V1008 and V1019, defective for the production of the competence activator, were as virulent as the wild-type strain. Autolysis involving an N-acetyl-muramyl-alanine amidase encoded by lytA was also regulated by calcium. The inserted allele lytA0::ery further reduced virulence in the dmb1 background (V2200). This additive effect of lytA- to dmb1 points to different routes of virulence regulation by LYT and DMB1 and suggests that the kinetics of calcium traffic controls several pathways involved in the virulence of pneumococcus.
肺炎链球菌是一种病原体，细胞外钙浓度在其生长、遗传转化感受态的诱导以及自溶激活过程中发挥着主要生理作用。这两种反应都受分泌到培养基中的一种蛋白质激活剂的调控。我们已经检测了改变感受态和自溶调节的突变对实验性毒力的影响。携带相关突变的同基因包膜衍生物是3型光滑克隆株，通过用来自3型光滑分离株的DNA转化相关粗糙菌株获得。用不同细菌培养物腹腔感染瑞士小鼠后，跟踪其存活动力学和血液中的细菌清除情况。在这个模型中，相对于野生型表现出毒力减弱的突变体分为两类。第一类以钙诱导自溶缺陷的lytA::ery突变体V1095为代表，毒力减弱与血液中细菌的快速清除有关。第二类以dmb突变体V2200和V3300为代表，毒力减弱与血液中细菌清除延迟有关，并且与钙转运动力学以及感受态和自溶调节的改变有关。V2200和V3300菌株毒力减弱似乎不太可能是其感受态表型的直接结果，因为感受态激活剂产生缺陷的com::ery突变体V1008和V1019与野生型菌株一样具有毒力。由lytA编码的涉及N - 乙酰 - 胞壁酰 - 丙氨酸酰胺酶的自溶也受钙的调节。插入的等位基因lytA0::ery在dmb1背景（V2200）中进一步降低了毒力。lytA对dmb1的这种累加效应表明LYT和DMB1通过不同途径调节毒力，并提示钙转运动力学控制了肺炎链球菌毒力涉及的多个途径。
