Protective effect of prophylactic penicillin on splenectomized mice exposed to an aerosolized suspension of type III Streptococcus pneumoniae

Prophylactic penicillin has been recommended for use in asplenic patients and postsplenectomy patients. A laboratory model using aerosolized pneumococci has been devised to test the effectiveness of prophylactic penicillin in a manner analogous to human experience. There is increased mortality, over time, in asplenic mice exposed to aerosolized type III Streptococcus pneumoniae. One hundred twenty-one male Swiss mice (mean weight 26 g) were divided into four groups: splenectomized, sham-operated, splenectomized + penicillin, and sham-operated + penicillin. After 2 wk the four groups were exposed for 30 min to an aerosolized atmosphere of 2.4 x 10⁹ colony-forming units of type III S. pneumoniae using a Tri-R model A-42 airborne infection apparatus. Penicillin was given at a daily intramuscular dosage of 40,000 units procaine penicillin G beginning 2 days prior to exposure and continuing through the third day after exposure. The splenectomized and sham-operated mice given penicillin showed significantly lower mortality (p<0.001) than mice not given penicillin.