Studies on the in vitro Drug Resistance of E. Coli towards Mixtures of Sulfonamides *

Although it is a well-known fact that drug resistance towards sulfonamides is easily obtained after a comparatively small number of exposures of the sensitive microorganisms to these drugs in vitro or in vivo,' there is, to our knowledge, no report in the literature concerning the influence that mixtures of different sulfonamides might have on the development of resistant strains. The wide use of combinations of three sulfonamides, which is due to the better solubility and the curtailing of by-effects particularly in reference to the kidneys,'6" made it seem desirable to investigate the influence of sulfonamide combinations on the development of drug resistance of bacteria. The individual components of these mixtures, as far as they were available, were of course studied at the same time. In addition, a new sulfonamide, 3,4-dimethyl-5-sulfanilamidoisoxazole (Gantrisin) was also tested because no experimental data on drug resistance were available for this compound. The development of drug resistance to this compound has apparently not been observed clinically and in one report the absence of this tendency has been specifically stressed.2 The results of these studies are given in the present paper.