With the belief that the therapeutic activity of sulfonamide drugs in pneumococcic infections depends in part on the presence of protective mechanisms other than the bacteriostasis produced by the drugs, a knowledge of the enhancement offered by normal serum is needed to clarify the mechanisms of this therapeutic action. The purpose of the present communication is to present experiments which deal with the activity of normal animal and human sera in enhancing the antipneumococcic action of sulfapyridine. Normal mouse, rabbit, guinea pig, rat, dog, infant human, and adult human sera were examined, with white mice used as test animals.
MATERIAL AND METHODSThe test to determine the enhancement of mouse protection produced by each serum consisted of the inoculation of graded doses of pneumococci to three series of mice, one series receiving serum alone, one series receiving sulfapyridine, and one series receiving both serum and sulfapyridine.The sulfapyridine was administered orally, mixed with the food. The food used was ordinary mouse biscuits, ground in a meat grinder and sifted through a fine sieve. The resulting powder was thoroughly mixed with sulfapyridine in the proportion of one part of the drug to ninety-nine parts of the powdered food, giving a one per cent sulfapyridine content. The mice were housed 6 in a cage, and the powdered food, with the sulfapyridine, given in open boxes, so that they had free access to it. The maximum protection with sulfapyridine alone resulted from its administration for from 3 to 6 days. There was approximately 33 per cent survival for Type I and survival varied from 20 per cent through 80 per cent with strains of Type III pneumococci. However, only 2-day sulfapyridine treatment was used in enhancement tests because comparisons were most clear cut with sulfapyridine dosage of this duration.The virulence of the cultures was such that 10' ml. of a freshly passed, 18-hour blood broth culture killed a mouse weighing 18 to 20 grams within 24 to 48 hours.Varying amounts of culture, 104, 10', 10' (1, 10 and 1,000 M.L.D.), were employed in the tests with Type I, and 104 to 0I ml. (1, 10, 100, 1,000, 10,000 and 100,000 M.L.D.), with Type III pneumococci. Dilutions were so adjusted that 0.5 ml. of each contained the desired amount of culture. The culture and serum were injected intraperitoneally, the serum immediately before the culture (within an interval of a few seconds).The dose of serum for each mouse was 0.5 ml., injected intraperitoneally.Surviving mice were discharged at the end of 7 days. Absorption tests were conducted in the following manner: Freshly passed cultures were grown for 4 hours at 370 C. The cultures were killed by heating at 550 C. for 30 minutes, centrifuged at high speed for one hour, and the "supernatant" discarded. The serum was added to the cells in the proportion of 1 ml. of serum to the sediment of 2 ml. of culture. The serum and cells were well mixed and placed in a water bath at 450 C. for one hour. Serum without cells was similarly kept in a water bath a...