Abstract

Fastness or resistance -to penic'illin and to sulfa drugs is known to occur in strains of bacteria which are sensitive to these chemicals; and in numerous instances on record this new property has been produced in vitro under experimental conditions. It is known that the degree of resistance can readily be increased by growing bacteria in a medium containing increasingly higher concentrations of such chemicals, and that the resistant strains so developed retain the property of resistance. My interest in this problem was to obtain quantitative data regarding the.origin of resistance and to determine whether or not a genetic interpretation could. be given to them. The preliminary summary of these results which has .been published (Demerec, '45) indicates that the change to penicillin-resistance in Staphylococcus aureus is a genetic change comparable to gene mutation.