Abstract
Strains of pneumococci. gonococci, E. coli and S. aureus have been rendered resistant in vitro to the bacteriostatic action of sulfonamide drugs. 1 , 2 , 3 , 4 , 5 , 6 Rammelkamp 7 has also observed that S. aureus may become “fast” to tyrothricin, both in vitro and in vivo. The present report is concerned with the in vitro and in vivo production of sulfonamide resistant strains of staphylococci.
The in vitro observations were made with 2 strains of S. aureus isolated from patients with severe staphylococcal infections. A chemically-defined medium as described by Gladstone was used throughout. 8 These strains were made resistant by exposure to increasing concentrations of sodium sulfathiazole in this medium. Initial growth was established with a minute inoculum from an agar slant. Subsequent transfers of the cultures in the synthetic medium were made with a 5 mm wire loop. The two strains showed an initial difference in susceptibility to the action of sulfathiazole. Strain 14 grew readily for several generations in the presence of 0.25 mg per 100 ml of sulfathiazole, but strain 7 was unable to institute growth in this concentration after the second transfer. It was necessary to start strain 7 in 0.1 mg per 100 ml. Control observations were carried out with the parent strains transferred an equal number of times in a drug-free medium.
The degree of growth was estimated regularly by measuring the density of the culture in the Evelyn photoelectric colorimeter, as previously described. 9 The development of drug resistance was determined by seeding approximately 1,000 organisms per ml to tubes of medium containing varying concentrations of sulfanilamide, sulfapyridine, sulfadiazine, and sulfathiazole.
Get full access to this article
View all access options for this article.