. Ciba Foundation symposium on drug resistance in micro-organisms: mechanisms of development. Drug resistance in microorganisms. Penicillin-induced Penicillin Resistance 87 or about 1 molecule per cell every 3 minutes—in logarithmic- ally growing cultures. Its penicillin sensitivity would suggest that such a very low level of formation is not of much benefit to the organism under conditions of the test. A chart summarizing most of the properties of these dif- ferent strains with respect to penicillinase production has been Table III Penicillinase activity and penicillin resistance of strains o
. Ciba Foundation symposium on drug resistance in micro-organisms: mechanisms of development. Drug resistance in microorganisms. Penicillin-induced Penicillin Resistance 87 or about 1 molecule per cell every 3 minutes—in logarithmic- ally growing cultures. Its penicillin sensitivity would suggest that such a very low level of formation is not of much benefit to the organism under conditions of the test. A chart summarizing most of the properties of these dif- ferent strains with respect to penicillinase production has been Table III Penicillinase activity and penicillin resistance of strains of B. cereus. NON-INDUCIBLE STRAINS 5 ("microconstitutive") ( parvo- constitutives') 569/h/i [oTI V ("000 [oT] ^^^ [m] s/b ("magncKonstitutive") I I (75,000). INDUCIBLE STRAINS 569 ("inducible") Induction *- 569 ' \ penicillin / (25,000) 'Deadaptation'by growth without penicillin ("semi-constitutive") 569/a Induction >569/A (K^OOo) penicillin (35^00o) S69/H ("pleno-constitutive"; [lol (75^000) Strains are denoted by numbers, 569, and presumed mutants therefrom by added letters, 569/H. Approximate rate of penicillinase production is given in circles as number of molecules per cell (assuming mean \vt. of one cell = l -3 X 10~i2 g )^ Figures in squares indicate the maximum concentration of penicillin (in units per ml.) allowing colony formation from at least 50 per cent of viable spores inoculated into nutrient agar. M= proved mutation. [M]= presumed mutation. compiled as illustrated by Table III, and a system of nomen- clature suggested. It is more or less self-explanatory; but certain comments are necessary. (1) Within the 5 group, the relation between rates of penicillinase production and penicillin resistance is obvious. There can hardly be any doubt that the one is responsible for the other. The reason for the relatively slight difference between the penicillinase resistance of 569 and 569/H has been asc
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