Fig 3. The Y. pestis Ymt mutant colonizes male fleas more efficiently than females following infection using mouse blood.

Infection rates for groups of female or male X. cheopis infected using mouse blood (blue symbols) or brown rat blood (red symbols) containing 1x10⁸–5.7x10⁸ CFU/ml GFP-positive KIM6+ or KIM6+ymtH188N Y. pestis were determined 1 day after infection by fluorescence microscopy of dissected flea digestive tracts A); or 0, 1, and 7 days after infection by CFU counts from individual triturated fleas (B, C). For A, each symbol represents the percentage of fleas containing GFP+ bacteria in their digestive tract. n = 4–10 fleas of each sex in 3 independent experiments (Table 1). For B and C, the mean and standard error (B) or median (C) of pooled data from 3 independent experiments for groups of 5–20 fleas infected using mouse blood are shown. *p < 0.05 by chi-square test (B) or two-way ANOVA with Tukey’s post-test (C). D) Examples of the foregut infection in female or male X. cheopis 1 day after ingesting KIM6+ymtH188N Y. pestis suspended in mouse blood (Left) or brown rat blood (Right). Scale bar = 50 μm.