Strains of E. coli were made resistant to aureomycin, bacitracin, catenulin, chloromycetin, circulin, dihydrostreptomycin, hydroxystreptomycin, neomycin, netropsin, penicillin, polymyxin B, streptothricin, terramycin, vinactin, and viomycin. The 4 internally related major groups these antibiotics fall into are: group 1: streptothricin, viomycin, vinactin (actinomyces polypeptides), catenulin, and neomycin (bacterial strains resistant to these are also resistant to the streptomycins, but the inverse does not hold true; complete cross resistance and cross dependence exist between hydroxystreptomycin and other streptomycins); group 2: aureomycin, chloromycetin, and terramycin; also penicillin and netropsin which are less closely related; group 3: polymyxin B and circulin (cyclic bacterial polypeptides) (bacteria resistant to these show a one-way cross resistance to streptothricin, catenulin, neomycin, and streptomycin); group 4: bacitracin (bacterial polypeptide). Increasing the sensitivity to one antibiotic by increasing resistance to another is termed collateral sensitivity. For example, E. coli in becoming 300 times more resistant to chloromycetin simultaneously develops a 100-fold increase in sensitivity to polymyxin B.