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 3.0 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, e.g. 569, and presumed mutants therefrom 

 by added letters, e.g. 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 

 ascribed to the very rapid induction of penicillinase formation 

 by penicillin in 569. Were it possible to inhibit penicillinase 

 induction without affecting growth, this point could be tested 



