Fig 2. Ymt⁻ and Ymt⁺ Y. pestis colonize female X. cheopis similarly when brown rat blood is used for the infectious blood meal, but not if mouse, human, or black rat blood are used.

Groups of female X. cheopis fleas that fed on mouse (blue), black rat (black), human (orange), or brown rat (red) blood containing 1.5x10⁸–1.1x10⁹ CFU/ml Y. pestis KIM6+, KIM6+ymtH188N, or KIM6+ymtH188N (pYmt) were scored for 1 week for A) the percentage of fleas that remained infected; B) the percentage that developed obstruction of the foregut (partial or complete blockage) that interfered with normal blood-feeding; and C) bacterial burden. Data are cumulative from 3 (KIM6+ and KIM6+ymtH188N groups) or 1 (KIM6+ymtH188N(pYmt) groups) independent experiments. Samples consisted of 7–20 female (A and C) or 25–220 fleas (roughly equal numbers of males and females; B) per experiment. The mean and standard error (A, B) or median (C) are indicated. *p < 0.05 by chi-square (A, B) or by Kruskal-Wallis test with Dunn’s post-test (mouse, human, and brown rat groups) or Mann-Whitney test (black rat group) (C). Dotted lines indicate the limit of detection (40 CFU). KIM6+ymtH188N(pYmt) was not used for black rat blood infections due to the limited availability of this blood.