TABLE 3.
Virulence of various Y. pestis KIM5 mutantsa
| Conditions and strain | Probit LD50 (Reed-Muench LD50) | 95% Confidence interval |
|---|---|---|
| Pregrowth at 28°C and pH 7 | ||
| KIM5 | 7 (8) | 4-10 |
| KIM5 Δailb | 21,000 (21,000) | 3,000-186,000 |
| KIM5 ΔpsaA | 530 (500) | 170-2,900 |
| KIM5 Δpla | 250 (280) | 76-58,000 |
| KIM5 Δail ΔpsaA | 940,000 (635,000) | NA |
| KIM5 Δail Δpla | 31,000 (64,000) | NA |
| KIM5 ΔpsaA Δpla | (24,000)c | NA |
| KIM5 Δail ΔpsaA Δpla | 420,000 (600,000) | 31,000-1,000,000 |
| KIM5 pCD1− | 30,000,000 (49,000,000) | NA |
| Pregrowth at 37°C and pH 7 | ||
| KIM5 | 27 (34) | NA |
| KIM5Δail | 220,000 (21,000) | 14,000-NUB |
Results of mouse virulence assays for Y. pestis KIM5 and mutant derivatives after i.v. inoculation. Mice were inoculated i.v. with 5- to 10-fold increasing doses of each strain. All mutants were tested at 10 animals/dose, and some mutants were tested in additional experiments with 4 to 8 animals/dose. Mice were observed for 16 days for survival, and LD50s were determined by probit analysis and the method of Reed and Muench (58). As a negative control, a pCD1− strain, lacking the Yop-encoding virulence plasmid, was included. In some cases, probit analysis was unable to assign confidence intervals (NA, not available), but Reed-Muench analysis gave similar LD50s. NUB denotes no upper bound for confidence interval.
Probit analysis was unable to calculate an LD50 (due to reduced mouse lethality at the highest infection doses, potentially due to immune clearance). In this case, we relied upon the Reed-Muench LD50, with the acknowledgment that this mutant has an unusual behavior in vivo.