Staphylococcal Penicillinase Characteristics of the Enzyme and Its Distribution

The penicillin inhibitor or penicillinase produced by certain strains of Staphylococcus has been the subject of experimentation in a number of laboratories. There is general agreement that the enzyme is present in many but not all strains of Staphylococcus, and it has also been held to be responsible for the "natural" resistance of some strains to the action of penicillin. In some studies characteristics have been attributed to the enzyme that are very difficult to explain in terms of the body of knowledge of enzyme chemistry. The demonstration of penicillinase did not long follow the beginning of intensive work on the antibiotic itself. Abraham and Chain (1940) were probably the first to call attention to its presence, and Harper in 1943 described a practicable method for its demonstration within the cells of bacteria. His method, of acetone and ether treatment of whole bacterial cells, has been used by all subsequent investigators. In their first studies, Bondi and Dietz (1944a,b) failed to find the enzyme in Staphylococcus. Later (1945), examining more strains, they demonstrated its presence in 14 per cent of them. They record the enzyme as present or absent, and find it invariably present in strains requiring more than 1 unit per ml of penicillin for inhibition. Kirby (1945) in a brief note stated that he had found penicillinase, using Harper's method, in 7 resistant strains, but not in 7 sensitive strains of Staphylococcus. Later 5 of the resistant, penicillinase-producing strains were studied in detail. The enzyme was assayed by adding the penicillinase, penicillin, and a culture of viable penicillin-sensitive organisms to nutrient broth. The growth of the indicating bacteria was followed turbidimetrically. On the basis of such assays, it was stated that the rate of action of the enzyme appeared to be independent of temperature between 2 and 37 C. Spink and Ferris (1945) reported after a preliminary study of 8 strains that organisms that acquired penicillin resistance in vivo produced penicillinase, whereas those whose resistance was induced in the laboratory did not. Later (1947), in an exhaustive study, these results were confirmed. The method of assay used by these workers consisted of adding 0.001, 0.01, or 0.1 mg of penicillinase to tubes of broth containing various quantities of penicillin. An inoculum of a penicillin-sensitive staphylococcus was then added, and the tubes were incubated for 48 hours. The destruction of penicillin was indicated by the development of turbidity after incubation. By this method they were able to demonstrate that the destruction of penicillin by penicillinase did proceed with time, but they were able to show only a rough correlation between the inactivation of penicillin and the concentration of penicillinase, a result that was at-