STUDIES ON SULFONAMIDE-RESISTANT ORGANISMS III. ON THE ORIGIN OF SULFONAMIDE-RESISTANT PNEUMOCOCCI

¹ From the Institute for Medical Research, Christ Hospital, Cincinnati, Ohio

Experiments were carried out to determine whether sulfonamide-resistant pneumococci are formed during the normal multiplication of a sensitive strain or whether they are produced in response to some action of the sulfonamide on the sensitive organisms. A quantitative study of the sensitivities of individual pneumococci composing a sensitive strain and the changes that occurred during conversion of this strain to a highly resistant strain showed that the pneumococci present after the first exposure to sulfapyridine were significantly more resistant than any organisms in the original sensitive strain. Within certain limits, organisms of increased resistance were formed upon each additional exposure to the drug. A comparison of the sensitivities of individual pneumococci composing other sensitive and resistant strains showed that in every instance the organisms that made up the so-called resistant strains were significantly more resistant than any pneumococci in the sensitive strains. These findings support the conclusion that highly resistant pneumococci are formed as a result of some action of the sulfonamide on the sensitive organisms.

It should be added that the individual pneumococci that make up either a sensitive or a resistant strain are not entirely identical in their reactions to a sulfonamide. These differences in the reactions of individual organisms in any strain are not to be confused with the large differences in sensitivity existing between so-called sensitive and highly resistant strains.