TABLE 5.

Virulence of A66 derivatives following i.v. and i.p. infection of XID (CBA/N) and normal (BALB/cByJ) mice

Mouse strain	Route	Infecting strain	Dose (log CFU)	No. dead /no. totala	Median time to death (h)
CBA/Nb	i.v.	A66	1.9	9/10	36
		AM188	2.0	8/10	88*c
		AM199	6.7	0/5**c
	i.p.	A66	1.9	10/10	35
		AM188	2.0	8/10	51*c
		AM199	2.7	0/5***c
BALB/c
ByJd	i.v.	A66	7.0	7/7	19
		AM188	6.9	1/7**c
		AM199	6.9	0/7***c
		AM201e	6.8	5/5	13
	i.p.	A66	2.9	7/7	35
		AM188	2.2	5/7	49***c
		AM199	2.2	0/7***c
		AM201	2.6	5/5	38

^aThe colony morphologies of bacteria recovered postmortem were identical to those of the bacteria in the inocula. 

^bThe i.v. and i.p. LD₅₀s of A66 in XID mice are <10 CFU (references 9 and 57 and unpublished data). 

^cSignificantly different from the value for A66 (*, P < 0.05; **, P < 0.005; ***, P < 0.0007). 

^dThe LD₅₀s of A66 in BALB/cByJ mice are 10⁵ CFU (i.v.) and <10² CFU (i.p.) (D. E. Briles, personal communication and unpublished data). 

^eCapsule production by AM201 was equivalent to that of its parent A66 (41.9 ± 4.4 and 41.5 ± 4.7 μg of capsule/ml of culture/unit of optical density at 600 nm, respectively).