TABLE 3.

Protective effect of passively transferred chinchilla antiserum against Hib challenge in the infant rat model of bacteremia^a

Group	Chinchilla serum	No. of animals bacteremic/no. challenged	Mean CFU/ 2.5 μl of bloodb	P
1	Anti-HtrA (wild type)	4/10	195	0.0054
2	Anti-H91A HtrA	4/10	330	0.0054
3	Anti-S197A HtrA	4/10	450	0.0054
4	Anti-MinnA	0/10	0
5	Normal chinchilla serum	10/10	500

^aFive-day-old infant rats were passively immunized s.c. with 0.1 ml of chinchilla antiserum or normal chinchilla serum. Twenty hours later, they were challenged intraperitoneally with freshly grown Hib strain MinnA (200 CFU, 0.1 ml). Blood samples were collected 20 h postchallenge via cardiac puncture and plated onto chocolate agar. Bacteria were counted after 1 day, and an animal was considered to be protected when no bacteria were recovered from its blood. The statistical significance of the number of bacteremic animals was established by the Fisher exact test. 

^bBacterial counts in the blood of infected animals.