GENETIC STUDIES ON MICROBIAL CROSS RESISTANCE TO TOXIC AGENTS I. ,

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Abstract
By means of the described gradient plate technic, strains of E. coli were obtained showing resistance to streptothricin, catenulin, neomycin, viomycin, vinactin, dihydroxystreptomycin, hydroxystreptomycin, aureomycin, chloramphenicol, terramycin, netropsin, penicillin, bacitracin, polymyxin B, and circulin. The degree of cross resistance was then detd. by testing the resistant strains against each antibiotic, using the gradient plate method for quantitative comparison. Four natural groups of antibiotics related by cross resistance were found. Collateral sensitivity was noted, in which resistance to one antibiotic is correlated with highly increased sensitivity to another. Advantages of cross resistance studies in classifying antibiotics and planning programs of chemotherapy are discussed.