(A) Two weeks after injection, severe tibiotarsal joint swelling was evident only in mice infected with 103 or 104 of B31. (B) However, severe tibiotarsal joint swelling could be observed in mice infected with 10, 102, 103 or 104 of N40D10/E9. Discussion Study of infectious bacterial species involving more than one virulent strain provides a more complete picture of the pathogenesis of the organism. B31 and N40 are two of the most widely examined B. burgdorferi strains in the USA to study Lyme disease pathogenesis. In 1997, B31
was the first B. burgdorferi genome that was published . We have recently determined this website that different laboratories use two different N40 strains under the same strain name . The genome of N40B was completed recently  but is not fully published. Our N40D10/E9 clone derivative is not yet sequenced but our critical evaluation has indicated that these two N40 strains are quite different even though both of them were isolated from the same tick . Indeed, based upon RST LRRK2 inhibitor and ospC types, both N40 strains are predicted to be a much less pathogenic strain than B31 [23, 32, 33, 98–100]. However, at least in one study, a higher percentage of mice infected with the sequenced N40 as compared to those with
B31 strain developed myocarditis (100% versus 92%). In addition, N40 showed both higher level of colonization in joints and arthritic lesions than that by B31 strain (60% versus 13%) in the infected mice . Such a comparative study has not been carried out with our N40D10/E9 strain. Therefore, we conducted thorough comparative analyses both in vitro and in vivo to assess their infectivity and ability to colonize various tissues
and cause disease. B. burgdorferi strains have been shown previously to bind to various mammalian cell types in vitro and in vivo[58, 60–64]. In this study, we selected Vero, EA.hy926, C6 glioma, and T/C-28a2 as representatives of epithelial, vascular endothelial, glial, and chondrocyte cells to study adherence of spirochetes in vitro. With the exception of Vero epithelial cells, B. burgdorferi Thymidine kinase strain B31 and strain N40D10/E9 showed approximately the same level of in vitro binding to various mammalian cells in this study. These results indicate the two most GSK458 studied B. burgdorferi strains, B31 and N40D10/E9, exhibit some differences in adherence despite sharing similar capability and mechanisms for adherence to various mammalian cells in vitro. Binding of B31 is significantly higher on Vero cells than N40D10/E9, but heparinase I treatment of these cells reduced binding of N40 strain much more dramatically (Figures 1A and 1B). These results suggest that a higher expression of surface proteins in B31 than N40D10/E9 that show affinity for host receptors other than heparan sulfate may be facilitating the attachment of this strain to Vero cells. Indeed, our study identifies BBK32 as one such candidate.