AN EXPERIMENTAL ANALYSIS OF THE CURATIVE ACTION OF PENICILLIN IN ACUTE BACTERIAL INFECTIONS

Abstract

The results of the experimental analysis reported in this and the two preceding papers (10, 11) indicate that in murine pneumococcal infections penicillin per se destroys the invading organisms only in those parts of the lesions where the bacteria are multiplying rapidly and are thus maximally susceptible to the bactericidal action of the drug. In areas where the bacterial growth rate is slowed, either because the pneumococci have reached a maximum population density, or because the accumulated exudate affords a relatively poor medium for rapid growth, the destructive effect of the antibiotic is greatly diminished. In such portions of the lessions the cellular defenses of the host are observed to play a major role in eliminating the bacteria. In sites where frank suppuration has developed, however, even the combined actions of the penicillin and the cellular defenses of the host are relatively ineffective in ridding the tissues of bacteria. Here, because of the poor medium provided by the pus, the pneumococci remain metabolically sluggish and therefore are not killed rapidly by the penicillin. At the same time the leucocytes in the necrotic exudate have deteriorated to the point where they cannot effectively perform their phagocytic functions. As a result, bacteria persist in such lesions for many days in spite of the most intensive penicillin treatment administered both locally and systemically.