TABLE 3.

Infection doses for different F. tularensis strains in C57BL mice^a

Strain	Genotype			Phenotype or complementation	No. of CFU (lethal dose)b
	FTT0918	pilA	FTT0086		Subcutaneous	Intraperitoneal
LVS1	−	−	Δ93 bp	LVS wt	3 × 107	1 × 101
LVS2	−	−	Δ93 bp	LVS wt	1 × 106	5 × 101
FSC688	−	+	Δ93 bp	LVS2, pilA in cis	5 × 103	3 × 101
FSC741	−	−	+	LVS2, FTT0086 in cis	2 × 106	NT
FSC693	+	−	Δ93 bp	LVS2, FTT0918 in cis	<5c	<5
FSC694	+	+	Δ93 bp	LVS2, pilA and FTT0918 in cis	<5	<5
FSC200	+	+	+	Type B wt	<5	<5
FSC767	−	+	+	FSC200, insertion mutation in FTT0918	2 × 102	<5

^aMice in groups of five were infected subcutaneously. The result is from one single experiment representative of three experiments of similar design. wt, wild type; Δ, deletion; NT, not tested.

^bThe CFU value is a 50% lethal dose (LD₅₀) calculation (26), but this should not be seen as a standard LD₅₀ experiment since mice were sacrificed if they showed severe sickness. A lethal dose indicated as <5 CFU was used for strains where all animals showed lethal symptoms of infection for doses between two and five bacteria.

^cThe infection kinetics was delayed compared to that for the pilA/FTT0918 double complementation (Fig. 5).