FIG. 4.
CspA is required for resistance to human serum. Wild-type (A), CspA mutant (B), CspA-complemented (C), and serum-sensitive (D) strains of B. burgdorferi were subjected to serum sensitivity assays. A total of 5 × 106 spirochetes were incubated with either 50% normal serum (•) or 50% heat-inactivated serum (▪) in triplicate. Samples were analyzed for the presence of motile spirochetes by dark field microscopy after 1, 4, and 16 h. Asterisks in panels B and D denote significant differences (P ≤ 0.05) in viability between similar samples incubated with NHS or heat-inactivated NHS.