FIG 5.

Sera from mice immunized with CspZ-YA had more robust levels of borreliacidal activity than those from CspZ-vaccinated mice. Sera from five C3H/HeN mice inoculated with CspZ, CspZ-YA, or PBS (negative control) were obtained at 42 dpii. Sera were serially diluted as indicated and mixed with guinea pig complement and B. burgdorferi strain B31-A3 (a and d) or 297 (b and e) or with B. afzelii strain VS461-JL (c and f) (5 × 10⁵ cells ml⁻¹). After incubation for 24 h, surviving spirochetes were quantified from three fields of view for each sample by using dark-field microscopy. The work was performed in three independent experiments. (a to c) The survival percentage was derived from the proportion of serum-treated to untreated spirochetes. Data shown are the mean ± standard error of the mean (SEM) of the survival percentage from three replicates in one representative experiment. (d to f) The 50% borreliacidal dilution of each serum sample, representing the dilution rate that effectively killed 50% of spirochetes, was obtained from curve-fitting and extrapolation of data from panels A to C. Data shown are the mean ± SEM of the borreliacidal titers from three experiments. The exact values are shown in Table S1 in the supplemental material. PBS-vaccinated mouse sera displayed no bactericidal activity (no killing [NK]). Statistical significance (P < 0.05, Mann-Whitney test) of differences in borreliacidal titers between groups are indicated (#).