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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.

The spirochetal agent of Lyme borreliosis, Borrelia burgdorferi, is able to induce an infection which develops in three stages: an early, localized infection, disseminated infection and a third stage, chronic infection, which probably indicates that a protected niche has been established in one or more tissues, where the spirochetes persist even if a specific immune response has been initiated. During the first stage, immediately after their entry into the host tissue, B. burgdorferi meet the motile phagocytic cells, neutrophils and monocytes; this is followed by consequent phagocytosis and killing. Although the rate and mechanism of this killing is not entirely clear, there is evidence that phagocytosis by both neutrophils and monocytes proceeds even in the absence of specific antibodies. We have demonstrated in both neutrophils and CHO Mac-1 (CR3 integrin) transfected cells, that one phagocyte receptor which is involved in B. burgdorferi adhesion in non osponic phagocytosis is the CR3 complement receptor known as integrin alpha m beta 2. Both recognition domains of the integrin, the iC3b site and the COOH terminal lectin site, bind to B. burgdorferi. Data presented here show that inhibition of adhesion on CR3 Mac-1 transfected cells and neutrophils is induced by mannose as well as by N-acetyl-D-glucosamine, sugars known to be specific inhibitors of the COOH terminal lectin-site of the integrin CR3. The inhibitory effect was serum complement independent. On the contrary, monoclonal antibody VIM12 directed towards the lectin domain not only failed to inhibit but improved adhesion, suggesting that, as a consequence of the binding, the integrin becomes more receptive to B. burgdorferi attachment at the I domain. Pretreatment of the borrelias with NalO4 eliminated adhesion, suggesting that the sugar residue/s recognized by CR3 is located on the bacteria.

Little is known about the distribution of Human Granulocytic Ehrlichiosis (HGE) in Europe and even less is known in Italy, where no case of clinically documented HGE has been reported. In a previous study we reported the presence of Ehrlichia DNA in Ixodes ricinus ticks from Central Italy. By the use of an Ehrlichia-specific PCR we found that 24% of the ticks were positive. Furthermore, we demonstrated a simultaneous coinfection of the same tick by both, Borrelia burgdorferi and Ehrlichia phagocytophila. Since the Friuli-Venezia Giulia region (North-east of Italy) is endemic for Lyme borreliosis (LB) and the geographic distribution of HGE usually overlaps that of LB, we decided to carry out a survey concerning the presence of Ehrlichia spp. in a recreational area near Trieste where the presence of Lyme borreliosis and Borrelia burgdorferi sensu lato in ticks is well demonstrated. Ticks were analyzed in pools (because a low infection rate was expected): eleven samples out of 93 were found positive by Ehrlichia-PCR. Subsequent sequence analysis of some of the positive PCR products revealed a high homology with the HGE agent Ehrlichia (only one base substitution in almost 450 bp sequenced). These findings add new and interesting data on the Ehrlichia epidemiology in Italy. By now we have demonstrated the presence of two distinct granulocytic ehrlichiae in Italiyn ticks by the aid of a PCR-based analysis: Ehrlichia phagocytophila in Central Italy and an HGE-like Ehrlichia in the north-eastern Italy, in a region close to Slovenia where the first reported case of HGE in Europe occurred.

A study to evaluate the natural rate of infection of Ixodes ricinus with Borrelia burgdorferi sensu lato was carried out in an endemic focus of Lyme disease in the Trieste area in northern Italy. Two-hundred and twenty-seven ticks collected in ten different stations were tested individually for the presence of the spirochetes using polymerase chain reaction techniques able to identify both Borrelia burgdorferi sensu lato and the four genospecies (Borrelia burgdorferi sensu stricto, Borrelia garinii. Borrelia afzelii and group VS116). Multiple infection of individual ticks was found. The infection rate ranged from 0-70%. Infection of Ixodes ricinus with Borrelia burgdorferi group VS116 was found for the first time in Italy in both a high and a low endemic focus of Lyme disease.