Analysis of mechanisms associated with loss of infectivity of clonal populations of Borrelia burgdorferi B31MI

Numerous studies have provided suggestive evidence that the loss of plasmid s correlates with the loss of infectivity of the Lyme disease spirochetes. In this study we have further investigated this correlation. Clonal populat ions were obtained from the skin of a mouse infected for 3 months with a cl onal population of Borrelia burgdorferi B31MI. The complete plasmid composi tions of these populations were determined using a combination of PCR and S outhern hybridization. The infectivities of clones differing in plasmid com position were tested using the C3H-HeJ murine model for Lyme disease. While several clones were found to be noninfectious, a correlation between the l oss of at specific plasmid and loss of infectivity in the clones analyzed i n this report was not observed. While it is clear from recent studies that the loss of some specific plasmids results in attenuated virulence, this st udy demonstrates that additional mechanisms also contribute to the loss of infectivity.