The effect of penicillin on the mortality of splenectomized mice exposed to an aerosol of Streptococcus pneumoniae type 3.

In experiment 1, splenectomized mice exposed to 1 X 10(9) colony-forming units (cfu) of type 3 Streptococcus pneumoniae experienced no mortality when given 40,000 or 4,000 units of procaine penicillin IM starting 2 days before exposure and continuing for 4 days. On day 5, Bicillin was given once in the same dosages. In experiment 2, splenectomized mice exposed to 2.2 X 10(9) cfu were significantly protected by 400 but not 40 units of penicillin when compared to controls (P less than 0.005). In experiment 3, splenectomized mice exposed to 2.7 X 10(9) cfu were significantly protected when compared to controls if 4,000 units of procaine penicillin were given either 2 days postexposure for 2 days followed by 1 day of Bicillin in the same dosage or 4 days postexposure with the same schedule and dosage (P less than 0.005 and 0.01, respectively) but not 6 days postexposure.