Classification of staphylococci by penicillin lysis.

It has been recognized for some time that staphylococci may be divided into those which do and those which do not produce a penicillinase (Hobby & Dawson, 1944; Spink, Ferris & Vivino, 1944; Kirby, 1945a, b) . Also, staphylococci are often tested for their penicillin sensitivity (tolerance) and classified as ‘sensitive’ or ‘insensitive’. The literature contains a number of references to another staphylococcal characteristic vis-d-vis penicillin which might be used as a third criterion of classification, namely penicillin lysis. The phenomena of autolysis and lysis by drugs are classical in bacteriology; the subject has recently been reviewed by Pulvertaft & Lumb (1948). Penicillin lysis of staphylococci was observed by Fleming (1929), Smith & Hay (1942) and Gardner (1945), and related to turbidity measurements by Chain, Duthie & Callow (1945) and Kirby (1945~). Knox (1945) and Todd (1945) related the occurrence of lysis to the growth-phase of the organisms, as did Chain et al. by making cell-counts and viable counts of their cultures. A comparison between the chemical activity of areas of lysis and areas of growth was made on assay plates by Pratt & Dufrenoy (1947), who showed that lipids were liberated in areas of lysis, and hydrolysed into fatty acids. The resistance of certain staphylococcal strains to lysis was noted by Kirby and by Knox, being associated with relative tolerance of the bactericidal action of penicillin. Kirby (1945 b ) also demonstrated the presence of penicillinase in unlysable, resistant strains. In view of the reports of Kirby and of Knox, a study was made of the correspondence between penicillin lysis, penicillinase production and penicillin ‘cell sensitivity’ (Luria, 1946) of a small number of strains of staphylococci, which were also tested for other characteristics.