Antibacterial activity of fortimicin A compared with those of five other aminoglycosides, and factors affecting susceptibility tests.

Fortimicin A, a pseudodisaccharide aminoglycoside, was found to have broad-spectrum activity against most clinically important aerobic and facultatively anaerobic bacteria, except Pseudomonas aeruginosa, some other Pseudomonas species, and streptococci. It was comparable to amikacin in its level of activity (minimum inhibitory concentrations) and spectrum of activity (except for the lack of activity on P. aeruginosa). Fortimicin A was bactericidal and was affected by cations when tested against P. aeruginosa. Minimum inhibitory concentrations were affected by the inoculum used in the susceptibility test. The drug was resistant to most aminoglycoside-inactivating enzymes, but probably is not active against permeability mutants.