BORRELIABAKTEERIN KYSTAMUOTO

[Bb]

Lähettäjä: Soijuv Lähetetty: 14.4.2004 12:07

Borreliabakteerin kyky muuntua kystamuotoon on ollut maailmalla jo pitkään tiedossa. Jostakin syystä siitä eivät täkälaiset lääkärit tiedä - puhumattakaan että tieto saisi muutoksia aikaiseksi hoitomuotoja mietittäessä. Tutkimuksen mukaan esim. borrelioosin hoidossa yleisimmin käytetty antibiootti, keftriaksone (Rocephalin), saa muita antibiootteja esim. tetrasykliinejä ja makrolidejä herkemmin bakteerin muuntumaan kystamuotoon (kyseinen ab ei tehoa kystamuotoiseen bakteeriin).

Koko artikkeli löytyy sivulta:

http://www.springer.at/periodicals/full ... 13_574.pdf


Cystic forms of Borrelia burgdorferi sensu lato: induction, development, and the role of RpoS

Rossella Murgia, Chiara Piazzetta, and Marina Cinco

Dipartimento di Scienze Biomediche, sez. Microbiologia, Università degli Studi di Trieste, Trieste, Italy

Summary. 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 β-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.

Key words: Borrelia burgdorferi, cystic forms, starvation, antibiotics, rpoS gene.

Introduction

Lyme borreliosis is a tick-borne zoonosis which develops through a peculiar polyphasic course, and one of the crucial questions still unanswered concerns the persistence of the infection. One of the arguments waiting to be clarified concerns "cystic forms" of Borrelia burgdorferi sensu lato (B. burgdorferi s.l.) and their possible role in resistance to antibiotic treatment, frequent relapses of the disease and spirochete survival in infected ticks. The first accurate report focusing on cystic forms was published in 1997 [1]. Similar and probably equivalent borrelial structures (gemmae, spheroplasts, L-forms) were described earlier [2?6] but were associated with spirochetal cells undergoing degenerative changes in a hostile environment (ambient changes, antibiotic treatment, host immune defence activity, aging of in vitro borrelial culture etc.).

Brorson et al. demonstrated that normal motile borreliae could develop from B. burgdorferi cysts and that the cysts were metabolically active, at least under in vitro conditions [2]. Further studies showed that motile spirochetes also matured from cysts formed in distilled water, even after being kept in such a medium for over a month [7].

Recent studies demonstrated that cyst suspensions of different ages can retain infectivity and induce illness in vivo, in a mouse model [8]. These experiments clearly indicate that cystic forms are not only a sign of spirochetal degeneration but might represent a state or phase of low metabolic activity of B. burgdorferi bacterial cells that allows the spirochete to survive in a hostile environment until conditions are favourable for the borreliae to grow and replicate again.

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. In addition, we investigated the possible role of the rpoS gene in cyst formation in the same experimental conditions. In Escherichia coli, RpoS controls a regulon of more than 30 genes, positively or negatively regulated, in response to starvation and transition to stationary phase [9, 10]. E. coli and other bacteria respond to nutrient starvation by entering a metabolic state referred to as stationary phase allowing them to survive environmentally unfavourable conditions such as oxidative stress, heat, high salts, and near-UV radiation [11 ? 13].

Since cystic forms are a consequence of some unfavourable conditions, we also wanted to investigate the possible involvement of the rpoS gene in cyst formation.

Therefore, we analyzed the conversion of borreliae to cystic forms in a B. burgdorferi sensu stricto rpoS mutant strain (M), with the rpoS locus inactivated by allelic exchange [14], in comparison with the rpoS wild-type organism (W).