Fig. 3.

yadBC confers a phenotype in skin. Pgm⁻ Lcr⁺ Y. pestis strains differing in the presence of the yadBC operon and activity of the Pla protease (CO92.S38 and CO92.S42; CO92.S39 and CO92.S43) were grown at 28 °C, and doses of approximately 5×10³ bacteria were injected intradermally into C57BL/6 mice. For comparison, the Pla⁺ pair of strains also was given 3 h at 37 °C prior to infection (28 °C/37 °C_3h). After 3 h, the infected skin was removed, homogenized and plated for viable bacterial numbers. Two additional ΔyadBC/yadBC⁺ pairs were grown at 28 °C and tested for recovery to assess the importance of the Lcr plasmid and pgm locus on the yadBC phenotype. These were the Pgm⁺ Lcr⁻ Pla⁺ strains CO92.S15 and CO92.S8 and the Pgm⁻ Lcr⁻ Pla⁻ strains CO92.S39 and CO92.S43. The recovery of viable numbers was normalized to the input dose for each strain and is presented as mean±sd. Open bars, ΔyadBC Y. pestis; closed bars, reconstituted strain (ΔyadBC/yadBC⁺). The data were pooled from multiple experiments: 4–6 experiments (14–23 mice per datum point) for the Pgm⁻ strains grown at 28 °C, two experiments (eight mice per datum point) for the Pgm⁺ strains, and four experiments (14–16 mice per datum point) for the Pgm⁻ strains grown at 28 °C/37 °C_3h. Statistically significant differences are indicated; n.s., not statistically significantly different.