Quantitative Action of Penicillin Inhibitor from Penicillin-Resistant Strains of Staphylococci

Abstract

The degree of resistance which a group of selected strains of staphylococci had for penicillin, as measured in vitro, was quantitatively related to the penicillin inhibitor produced by these strains. Crude inhibitor from resistant strains inactivated varying concs, of penicillin over a period of time in a quantit. manner, the time needed being dependent upon the amts. of inhibitor and concs. of penicillin. The strains were derived from human patients, 2 strains being naturally penicillin-resistant and 5 others resistant due to therapy. Their sensitivity was detd. in Gladstone''s synthetic and water-clear medium at 37[degree]C. To detmn. potency of the inhibitor, the inhibitor was extracted from a conc. suspension of organisms by Harper''s method, the bacteria dried and tested for sterility. 0.1 ml. of a 10-3 dilution of a 24-hr, sensitive staph. culture was added to tubes with Gladstone''s medium and increasing concs. of penicillin. 0.01 or 0.1 mg. of dried bacteria were added and the tubes left at 37[degree]C for 48 hrs. To detmn. the quantit. action of inhibitor, the same amt. of dried bacteria was added to tubes prepared as above and kept at 37[degree] C. The density of the culture was measured colorimetrically for 60 hrs.