Study On Pathogenicity And Infection Mechanism Of Borrelia Burgdorferi Sensu Lato From Northeastern China

Borrelia burgdorferi sensu lato is the causative agent of Lyme disease. To study the pathogencity of B. garinii and B. afzelii isolated from northeastern China. C3H/HeN mice were subcutaneously inoculated with 10⁵ B. garinii strain JW1, purified strain JW1, B. afzelii strain VH7 and B. burgdorferi sensu stricto strain B31 respectively. JW1 cause severe damages in joint and kidney, mild damages in brain of C3H mice. But the high passages purified strain JW1 (20^th passage) losed the infectious ability. The strain VH7 and B31 only caused damages in joint of C3H mice. These findings suggested that the B.garinii strain JW1 was the strongest virulent strain.In the study, the diversity of 18 B. burgdorferi strains from northeastern China was analyzed based on ospC gene. They were classified into 12 groups, Eight of which were B. garinii, and the other 4 were B. afzeli. Except one B. afzelii strain fall into A1 group, the other 3 were distinct from the known invasive groups. The pathogenical experiments indicated that the JW1 group was highly virulent followed by the NMK3 group, and the VH7 group had relatively low virulence. The analysis of the ospC sequences showed that lateral transfer and recombination existed between ospC gene of B. garinii and B. afzelii in northeastern China.As an initial effort to elucidate the molecular mechanisms of Borrelia host adaptation, we employed two-dimensional gel electrophoresis (2D-PAGE) coupled with matrix-assisted laser desorption/ionization-time of flight mass Spectrometry (MALDI-TOF-MS), and compared the protein profiles of B. garinii strain JW1, one of the major species of the Lyme disease agents found in Eurasia, under the conditions mimicking either the phase of tick colonization or the phase of mammalian host infection. Out of 76 proteins selected, twenty five were identified successfully by peptide mass fingerprinting, which included some enzymes involving in glycolysis, carbon fixation and glycerolipid metabolism pathways; membrane-associated protein P66; a key ehemotaxis response regulator CheY-3; and some stress proteins, molecular chaperone, heat shock proteins and translation elongation factors. It was suggested that during the shift from 'tick-like' to 'mammal-like' condition, the spirochete up-regulated the enzymes involving in metabolism and so accelerated the carbon fixation, triacylglycerol and lipotechoic acid biosynthesis for growth in large amount and thus prepare to invade to mammalian hosts. The bacterium also accelerated the biosynthesis of the components of flagellum, motor proteins and switch proteins through up-regulating the expression of CheY-3 to enhance the motility of the pathogen. Thirdly, it strengthened adhesion to the host receptor integrinα_vβ₃ by increasing the numbers of P66 and so as to establish infection and colonization within various tissues.In order further to investigate the pathogenicity of B. burgdorferi sensu lato, the recombinant shuttle plasmid with luminescence gene was constructed. But the transformation of the plasmid into B. garinii was not accomplished, suggesting there is an obstacle in B. garinii transformation and the mechanism of which should be explored.