Fig. 5.

Restoration of urease activity in Y. pestis does not affect infection and blockage rates in fleas that survive the initial acute toxicity. (A) Cumulative blockage rate 4 wk after infection with wild-type Y. pestis KIM6+ or the urease-positive mutant Y. pestis ureDΔG. At least 110 fleas were analyzed per sample. (B) Percentage of fleas infected initially and after 4 wk. (C) Mean bacterial load (cfu) in infected fleas at different times after the infectious blood meal (15–20 fleas per strain and per trial). Data are the mean ± SEM of two trials. NS, nonsignificant difference.