FIG. 1.

The number of Y. pseudotuberculosis in infected fleas decreases over time. The change (n-fold) in CFU/flea (mean CFU/flea on day 28 divided by mean CFU/flea immediately after infection) was determined separately for Y. pseudotuberculosis strains K163, K174, and K177 (A) and IP32953, PB1, PB1 ΔddhD-wzz, PB1 ΔddhD-wzz(pHMS1.2), IP32951, K170, K175, K177, K186, and K199 (B) and for Y. pestis KIM6⁺ (C). The mean and standard error of the mean of the change (n-fold) in CFU are shown for each group; the mean CFU/flea for each time point was determined from samples of 20 fleas per strain except where noted in Table 1.