FIG 2.

Δbb0318 spirochetes demonstrate sensitivity to H₂O₂ and murine macrophages. (A) A total of 1 × 10⁴ mid-log-phase wild-type (WT), Δbb0318/pBSV2G, or Δbb0318/pBSV2G bb0318 spirochetes were either left unexposed or exposed to 10 mM, 15 mM, or 20 mM exogenous H₂O₂. Following a 2-h incubation, spirochetes were serially diluted and were plated for CFU. (B) A total of 5 × 10⁴ mid-log-phase WT, Δbb0318/pBSV2G, or Δbb0318/pBSV2G bb0318 spirochetes were incubated in the presence or absence of J774 murine macrophages for 4 h. Spirochetes were serially diluted and were plated for CFU. The percentage of survival of each clone under each challenge condition was calculated by dividing the number of CFU in the presence of the challenge by the number of CFU for the matched medium-alone control, multiplying by 100, and subtracting from 100%. Data are averages ± standard deviations for at least three biological replicates for each clone and are plotted on a logarithmic scale. Data sets were compared across clones by use of one-way ANOVA and Tukey's posttest (GraphPad Prism, version 6.0). Statistical comparisons were not found to be significant unless otherwise noted. Asterisks indicate significant differences (P < 0.05) from wild-type and/or Δbb0318/pBSV2G bb0318 spirochetes.