Multiple drug resistance inAerobacter aerogenes

Abstract

Multiple drug resistance resulting from continued growth in various drugs in turn followed by serial subculture in the simultaneous presence of all the drugs has been studied. In this way strains ofA. aerogenes resistant, in considerable measure, to 3, 4 and 5 drugs have been obtained. Although the final state was always a compromise between the various new properties it was often a good and very effective compromise and for this reason kinetic properties of the cells such as growth rate had to be intensively followed. Tests for presence or absence of growth after a fixed interval of time would not have sufficed. At the 5-drug stage a good compromise was obtained when the agents used were streptomycin, sulphanilamide, chloramphenicol, ampicillin and 5-aminoacridine. When tretamine (triethylene melamine) replaced 5-aminoacridine as the fifth drug, the rate of growth in the various drugs both singly and in admixture was not as good.

Continued subculture in sulphanilamide medium led to a condition of hypersensitivity to chloramphenicol. Ampicillin-resistant strains were more inhibited by 2-phenylethanol than the ampicillin-sensitive parent organism. Strains resistant to chloramphenicol were also resistant to tretamine and vice versa. Such cross-resistance did not occur with any of the other drugs at the concentrations used.