The susceptibility of penicillinase-producing bacteria to penicillin; the effect of sodium azide.

In a previous publication Bondi and Dietz (1947) reported that various factors could influence the susceptibility of penicillinase-producing bacteria to penicillin. The authors concluded that individual cells of certain organisms that produce this enzyme may be just as susceptible to penicillin as those of organisms that do not produce penicillinase. In a continuation of this study, the effect of sodium azide on the susceptibility of penicillinase-producing organisms has been studied to determine further the mechanisms that influence their susceptibility to this antibiotic. Woodruff and Foster (1945) studied the effect of various agents on penicillinase activity and found ferrous chloride, iodoacetic acid, and sodium azide to have an inhibitory effect. Two groups of workers, Benedict, Schmidt, and Coghill (1945) and Henry and Housewright (1947), were unable to show an effect by sodium azide on this enzyme. Treffers (1946), in studying the potentiation of penicillin by various agents, concluded that sodium azide, iodoacetic acid, and many other compounds could enhance the action of penicillin without involving the inhibition of penicillinase. The sodium azide used in this study was prepared from a 1 per cent stock solution in sterile distilled water. This solution was allowed to remain at room temperature overnight and added aseptically to 1 per cent tryptone broth to give the desired concentration. Stock solutions of crystalline potassium penicillin G in sterile saline, 2,000 Oxford units per ml, were kept frozen until used. Fresh penicillin solutions, in the concentrations desired, were prepared from the stock solutions regularly. The cultures of staphylococci studied were taken either from a stock culture collection or isolated from routine hospital specimens. Staphylococcus X-3 "resistant" was obtained by isolation of a resistant variant from the parent culture by passage through broth containing increasing concentrations of penicillin. The latter organism did not gain the ability to produce penicillinase. Preliminary experiments were run to determine the highest concentration of sodium azide that would not appreciably affect the growth of the organism tested. This was accomplished by adding different concentrations of the chemical to 1 per cent tryptone broth and inoculating sets of such broths with cultures of staphylococci. From the results, summarized in table 1, 0.02 per cent sodium