HETEROGENEITY IN THE COMPLEMENT-DEPENDENT BACTERIOLYSIS WITHIN THE SPECIES OF BORRELIA-BURGDORFERI

Sixteen Borrelia burgdorferi strains, including all three species, wer e compared in a colorimetric bactericidal assay for their ability to e scape the complement-dependent bacteriolysis on incubation in normal h uman serum free of specific antibodies (NHS). The species B. afzelii w as found to be serum resistant (EB1, EB3, FEM1, FEM2, Pko), whereas st rains of the species B. garinii were found to be serum sensitive (1/B2 9, G1, G2, PSth, PBr, PTrob). Six strains, mainly B. burgdorferi sensu stricto, were only partially sensitive (Z25, 297, B31, PKa-I, PBi). A ll strains activated the complement cascade in NHS, whereas only four strains (G1, G2, PBr, PSth) could activate complement in the presence of EGTA-Mg. After complement activation, covalently bound C3 fragments (C3b, iC3b) were detected on serum-sensitive as well as serum-resista nt borrelial strains. Heterogeneity, however, was observed between ser um-resistant and serum-sensitive strains with respect to deposition of C6 and C9. Whereas serum-sensitive strains were strongly positive for C6 and C9 and were, therefore, killed by the terminal complement comp lex (TCC), serum-resistant strains were devoid of C6 and C9 on their c ell surface. The serum resistance may, therefore, be due to an absent or only transient formation of TCC on the bacterial surface.