TABLE 1.

Pathogenicity of GBS with one- or nine-repeat alpha C protein in immune and nonimmune mice^a

Challenge strain	LD50 after immunization with:
	One-repeat antiserum	Nine-repeat antiserum	Preimmune antiserum
One-repeat A909	5.5 × 104	1.6 × 103	1.0 × 103
Nine-repeat A909	2.4 × 105	1.8 × 105	2.4 × 103
P value	0.3842	0.0073b	0.5813

^aLD₅₀s were calculated by using the logistic regression procedure. Mice were immunized with rabbit antiserum elicited to one- or nine-repeat alpha C protein. Pups were challenged with 0.05 ml intraperitoneally within 48 h of birth. The range of the challenge dose was 5 × 10² to 5 × 10⁷/mouse. Survival was determined 48 h after challenge. 

^bSignificant difference between LD₅₀s of GBS with one- and nine-repeat alpha C proteins.