The antibiotics, polymyxin A B C D and E, have been described in the recent literature. Their antibacterial spectra are similar. They differ from one another in amino acid content. It is the purpose of this presentation to describe our studies of the antibacterial activity, pharmacology, untoward reactions, and clinical experience with polymyxin B and polymyxin E.5 IN VITRO ACTIONWe found that the susceptibility to polymyxin of 78 strains of ten different genera by the tube dilution test (Table I) is marked against Salmonella, Shigella, Klebsiella, microorganisms of the coli aerogenes groups, and most importantly, Pseudomonas. Brucella and many staphylococci are moderately sensitive, while Proteus and hemolytic streptococci are refractory. It is of interest that a strain of Pseudomonas, which developed high resistance to streptomycin in three daily transfers, did not become resistant to polymyxin after 27 transfers. Size of inoculum and human serum reduced but slightly polymyxin activity. The concentration of polymyxin required to inhibit Klebsiella and Pseudomonas is not reduced significantly by the addition of subinhibitory amounts of streptomycin, aureomycin, sulfadiazine or penicillin, either singly or in several combinations. Polymyxin antagonizes the cumulative streptomycinpenicillin action on Proteus.

No abstract

No abstract

No abstract

No abstract