Enzymatic inactivation of a new aminoglycoside antibiotic, sisomicin by resistant strains of Pseudomonas aeruginosa.

The antibacterial activity of sisomicin (SS), a new aminoglycoside antibiotic active toward clinical isolates of Pseudomonas aeruginosa, was determined and compared with that of the gentamicin C complex. Both drugs were effective against these strains and showed almost the same antibacterial activity. A few strains were found to be resistant to SS. The antibiotic was inactivated by a cell-free extract from the SS-resistant strains due to acetylation of the drug. Comparative studies of the inactivation of the drugs which lack a 6'-amino group in the amino sugar linked to 2-deoxystreptamine strongly suggested that SS inactivation was due to acetylation of the 6'-amino group of the 4',5'-didehydropurpurosamine moiety.