Cepacin A and cepacin B, two new antibiotics produced by Pseudomonas cepacia.

Two new acetylenic antibiotics, cepacins A and B, have been isolated from the fermentation broth of Pseudomonas cepacia SC 11,783 and assigned structures 1 and 2. Cepacin A has good activity against staphylococci (MIC 0.2 micrograms/ml) but weak activity against streptococci (MIC 50 micrograms/ml) and the majority of Gram-negative organisms (MIC values 6.3 approximately greater than 50 micrograms/ml). Cepacin B has excellent activity against staphylococci (MIC less than 0.05 micrograms/ml) and some Gram-negative organisms (MIC values 0.1 approximately greater than 50 micrograms/ml).