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ABSTRACTA virulent, low-passage culture of a tick-derived strain of Borrelia gariniiwas subjected to serial in vitro passages, from which inoculations were made into C3H/HeN mice. A full display of pathogenicity was observed through passage 4, as measured by cultures of ear punch biopsy samples and internal organs and determination of tibiotarsal joint swelling. Decreased dissemination through skin and infection of internal organs were observed beginning at passage 6. These losses correlated with both the selection of clones harboring 21% less flagella than the parent strain, as seen by electron microscopy, and loss of the motility of the higher passages, as demonstrated by a swarm assay. However, during the chronic phase (3 months after infection), spirochetes were cultured from the bladder and kidney of a mouse inoculated with passage 12. The kidney isolate had the same number of flagella and motility as the original low-passage isolate. Although we can't exclude the possibility that other subtle variations may be arising given the uncloned nature of the isolate, we have found a strong association between loss of flagella and decreased invasiveness. Arthritogenicity progressively decreased with passages, so that only 12.5% of chronically infected mice inoculated with passage 29 still presented with joint swelling, concurrent with a decrease in the staining intensity in a Southern blot with a vlsE-based probe. These results suggest a multifactorial model in which the number of flagella drives the invasiveness of this agent, while plasmid-associated factors are responsible for triggering arthritogenicity.

ABSTRACTFifteen Borrelia burgdorferisensu lato isolates from questing ticks and skin biopsy specimens from erythema migrans patients in three different areas of Spain were characterized. Four different genospecies were found (nine Borrelia garinii, including the two human isolates, three B. burgdorferisensu stricto, two B. valaisiana, and one B. lusitaniae), showing a diverse spectrum of B. burgdorferisensu lato species. B. gariniiisolates were highly variable in terms of pulsed-field gel electrophoresis pattern and OspA serotype, with four of the seven serotypes described. One of the human isolates was OspA serotype 5, the same found in four of seven tick isolates. The second human isolate was OspA serotype 3, which was not present in ticks from the same area. Seven B. gariniiisolates were able to disseminate through the skin of C3H/HeN mice and to cause severe inflammation of joints. One of the two B. valaisianaisolates also caused disease in mice. Only one B. burgdorferisensu stricto isolate was recovered from the urinary bladder. One isolate each of B. valaisianaand B. lusitaniaewere not able to disseminate through the skin of mice or to infect internal organs. In summary, there is substantial diversity in the species and in the pathogenicity of B. burgdorferisensu lato in areas in northern Spain where Lyme disease is endemic.