Borrelia burgdorferi B31 cells lacking all linear plasmids or all but the 49-kb linear plasmid expressed the otherwise silent gene for the outer membrane protein OspC. In the first demonstration of a function for a circular plasmid of Borrelia spp., ospC was located on a 27-kb circular plasmid of B31.

The genes coding for the outer surface protein A (OspA) of 19 different Borrelia burgdorferi strains belonging to the seven OspA-serotypes 1-7, previously described [Wilske et al. (1993) J Clin Microbiol, 31: 340-350], have been investigated. B. burgdorferi sensu lato strains were chosen from various biological sources (ticks, human skin and cerebrospinal fluid) as well as different geographical origins (Germany, Slovenia, Austria, United States). The open reading frames of all ospA genes consist of 819-825 nucleotides corresponding to proteins of approximately 30 kDa. The ospA sequences obtained in this study and previous published studies were compared with the results from OspA serotyping with monoclonal antibodies. The classification into the seven OspA serotypes could be confirmed on a genetic basis (ospA genotypes 1-7) for all strains analyzed so far (n = 29). In addition, one strain without OspA expression could be assigned to ospA genotype 2. Genetic stability could be proven for the ospA gene of B. burgdorferi strain PWudI after inocculation and reisolation from a gerbil. However, we found evidence for intragenic recombination by cluster analysis of ospA sequence data. Accordance of ospA genotype 1 strains with B. burgdorferi sensu stricto and ospA genotype 2 strains with B. afzelii, as well as the ospA genotype strains 3-7 with B. garinii was confirmed by pulsed-field gel electrophoresis of MluI-digested genomic DNA. B. garinii is not only more heterogeneous in respect to the OspA-encoding genes, but shows moreover major subgroups formed by genotypes 4, 5 and 6 and genotypes 3 and 7, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Borrelia burgdorferi-related isolates were tested for their sensitivity to normal human serum (NHS) and their ability to activate complement. By dark-field microscopy, electron microscopy, and subsurface plating, it was shown that exposure of a Borrelia garinii isolate to 10% or more NHS resulted in immobilization, blebbing, and killing of the spirochetes. These effects were mediated by complement, since they were not seen after heat treatment of NHS, in the presence of EDTA, or in an agammaglobulinemic serum. All seven B. garinii type 5 or 6 and all four VS116/M19 strains were serum sensitive, whereas all eight Borrelia afzelii, five of eight B. garinii type 4, and three of seven B. burgdorferi sensu stricto isolates were serum resistant. The other isolates were partially serum sensitive. Four serum-sensitive B. garinii isolates had been isolated from human cerebrospinal fluid. Most likely, activation of both the alternative pathway and the classical pathway of complement was involved, since bactericidal activity was diminished in properdin-deficient sera as well as in a C1q-depleted serum and in a C4-deficient serum. Bactericidal activity could be restored when a serum lacking C1q or C4 was mixed with a properdin-deficient serum. Isolates with various genetic backgrounds were equally able to activate C3 as measured by enzyme-linked immunosorbent assay. In the presence of Mg-EGTA, C3 was activated by all isolates after exposure to >10% NHS. This study shows that B. burgdorferi-related spirochetes can be either serum sensitive or serum resistant in vitro and that this characteristic is associated with their genetic background. Lyme borreliosis (LB) is a multisystem disorder caused by the tick-borne spirochetes Borrelia burgdorferi sensu stricto, Borrelia garinii, and Borrelia afzelii. Erythema migrans (EM), a skin lesion surrounding the site of the initial tick bite, is often the presenting symptom of LB (54). Subsequently, spirochetes can disseminate to other skin sites, resulting in multiple EM lesions and finally acrodermatitis chronica atrophicans (ACA), or to various organs, such as the heart, the joints, the eyes, or the central nervous system (54). Dissemination of Borrelia from the skin to distant sites is generally considered to occur hematogenously. After needle or tick-borne inoculation of mice with B. burgdorferi, all inoculated mice had positive blood cultures up to 6 weeks postinoculation (p.i.), while after 1 year only 1 of 10 mice was positive (6). Spirochetes have been cultured in low frequency from blood from rabbits 2 weeks p.i. (26) and from rhesus monkeys 1 to 6 weeks p.i. (41), although in another study blood cultures from such animals were negative (37). Culture of spirochetes from human blood has been successful in a few cases (7, 34, 58) but is usually negative (35). These findings suggest that spirochetes are present in the circulation in the early stage of infection but that they disappear in later stages of the disease. Whether the humoral immune system plays a role in the prevention o...

Among Borrelia burgdorferi sensu lato isolates, seven outer surface protein A (OspA) serotypes have been described: serotypes 1 and 2 correspond to B. burgdorferi sensu stricto and Borrelia afzelii, respectively, and serotypes 3 to 7 correspond to Borrelia garinii. In Europe, serotype 4 has never been isolated from Ixodes ricinus ticks until recently, although this serotype has been frequently isolated from cerebrospinal fluid from patients. In Europe, B. afzelii and B. burgdorferi sensu stricto were found associated with rodents and B. garinii was found associated with birds. In this study, the reservoir role of Apodemus mice for B. garinii OspA serotype 4 was demonstrated by xenodiagnosis. Apodemus mice are the first identified reservoir hosts for B. garinii OspA serotype 4.

In Europe, Borrelia garinii OspA serotype 4 has been isolated from the cerebrospinal fluid of patients but, up to now, has never been identified among culture isolates from Ixodes ricinus ticks. This information raises the question of whether OspA serotype 4 is transmitted by I. ricinus in nature. In the present study, I. ricinus nymphs collected in an area of endemicity in southern Germany were allowed to feed on mice. Cultivation of ear biopsy specimens showed that six of seven B. garinii-infected mice were infected by OspA serotype 4. In contrast, very few B. garinii OspA serotype 4 organisms were isolated directly from the ticks which infected the mice; most isolates were B. afzelii. The infected mice transmitted mainly OspA serotype 4 to xenodiagnostic ticks, preferentially in combination with B. afzelii.