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Antibiotic action of pyocyanin

Biologically produced pyocyanin was purified, and the nature of its antibacterial action was determined for several bacteria. The pigment was shown to be bactericidal for all susceptible organisms. The bactericidal effect was dependent upon pyocyanin concentration and resulted in decreases in viability ranging from 1 to 8 log viable cells ml-1. The gram-positive bacteria were more susceptible as a group to the antibiotic action than were the gram-negative bacteria. All apyocyanogenic pseudomonads tested were totally resistant to the pigment, suggesting that resistance may be a characteristic of the genus. Pseudomonas aeruginosa, the producer organism, was also essentially unaffected by high concentrations of pyocyanin. Facultative anaerobes were twofold or more times resistant to the action of the pigment under fermentative conditions; however, the antibiotic action did not require oxygen since denitrifying bacteria were more susceptible during anaerobic respiration than during aerobic respiration.