Murgia Rossella, Piazzetta Chiara, Cinco Marina
Dipartimento di Scienze Biomediche, sez. Microbiologia, Università degli Studi di Trieste, Trieste, Italy.
Wien Klin Wochenschr. 2002 Jul 31;114(13-14):574-9.
It has been demonstrated recently that cells of Borrelia burgdorferi sensu lato, the etiological agent of Lyme disease, transform from mobile spirochetes into nonmotile cystic forms in the presence of certain unfavourable conditions, and that cystic forms are able to reconvert to vegetative spirochetes in vitro and in vivo. The purpose of this study was to investigate the kinetics of conversion of borreliae to cysts in different stress conditions such as starvation media or the presence of different antibiotics. Using the same experimental conditions we also investigated the possible role in cyst formation of RpoS, an alternative sigma factor that controls a regulon in response to starvation and transition to stationary phase. We observed that beta-lactams penicillin G and ceftriaxone, the antibiotics of choice in Lyme borreliosis treatment, favoured the production of cysts when used with serum-depleted BSK medium. In contrast, we observed a low level of cyst formation in the presence of macrolides and tetracyclines. In order to elucidate the role of the rpoS gene in cyst formation we analyzed the reaction of the rpoS mutant strain in comparison with its wild-type in different conditions. Under the same stimuli, both the wild-type borrelia and the rpoS knock-out isogenic strain produced cystic forms with similar kinetics, thus excluding the participation of the gene in this phenomenon. Our findings suggest that cyst formation is mainly due to a physical-chemical rearrangement of the outer membrane of Borrelia burgdorferi sensu lato leading to membrane fusion and controlled by different regulation mechanisms.
最近有研究表明，莱姆病的病原体——伯氏疏螺旋体狭义种的细胞，在某些不利条件下会从活动的螺旋体转变为不活动的囊状形式，并且囊状形式能够在体外和体内重新转变为营养型螺旋体。本研究的目的是调查在不同应激条件下，如饥饿培养基或存在不同抗生素时，伯氏疏螺旋体转变为囊肿的动力学。使用相同的实验条件，我们还研究了RpoS（一种替代的σ因子，可响应饥饿和向稳定期的转变来控制一个调节子）在囊肿形成中可能发挥的作用。我们观察到，β-内酰胺类的青霉素G和头孢曲松（莱姆病治疗中首选的抗生素）与血清耗尽的BSK培养基一起使用时，有利于囊肿的产生。相比之下，在大环内酯类和四环素类存在的情况下，我们观察到囊肿形成水平较低。为了阐明rpoS基因在囊肿形成中的作用，我们分析了rpoS突变株与其野生型在不同条件下的反应。在相同刺激下，野生型伯氏疏螺旋体和rpoS基因敲除的同基因菌株产生囊状形式的动力学相似，因此排除了该基因参与这一现象的可能性。我们的研究结果表明，囊肿形成主要是由于伯氏疏螺旋体狭义种外膜的物理化学重排导致膜融合，并受不同调节机制控制。
