Comparative Action of Aureomycin, Chloromycetin, Neomycin, Q-19, and Polymyxin B Against Gram Negative Bacilli

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Abstract
Twenty strains each of Escherichia coli, Aerobactor aerogenes, Proteus vulgaris, and Pseudomonas aeruginosa were tested for sensitivity to neomycin, Q-19, aureomycin, chloromycetin, and polymyxin B. Q-19 an antibiotic from Bacillus circulans, and polymyxin B were particularly effective against P. aeruginosa. Neomycin and chloromycetin were most effective against Proteus. Most of the strains of E. coli and A. aerogenes were susceptible to the action of all 5 antibiotics. Only 5 of the 80 strains tested were not sensitive to 31.2 [mu]g. or less of neomycin. The degree of resistance possessed by variants of E. coli exposed to Q-19 and neomycin is low. These variants display the "penicillin" rather than the "streptomycin" type of drug resistance. Q-19 and neomycin are bactericidal in a concn. equal to or only slightly higher than that in which they are bacteriostatic.