TABLE 1.

LD₅₀ and mean day to death for WT and mutant strains^a

Strain	Genotype	LD50 (CFU)	Mean day of death
RM12	WT	<10	9
RM40	hilA::tet	<10	14
RM69	Δspi1::kan	3.4 × 103	13

^aGroups of four animals were infected with 10, 100, 1,000, or 10,000 CFU of each strain and followed for 3 weeks. LD₅₀ was determined by the Reed-Muench formula.