Gene Cassette Encoding a 3-N-Aminoglycoside Acetyltransferase

The large number and variety of antibiotic resistance genes found in gene cassettes associated with class 1 integrons in multiply antibiotic-resistant organisms have always indicated the existence of a large pool of gene cassettes from which they are drawn (10). The discovery of integrons, sometimes harbor-ing very large arrays of gene cassettes, in the chromosomes of many different bacteria has confirmed the existence of this pool, but to date very few cassettes containing resistance genes have been found among these cassettes. Known examples are the catB9 (12) and blaP7 (blaP9) (7, 8) cassettes found in the cassette arrays of different Vibrio cholerae strains. Though 3-N-aminoglycoside acetyltransferases [AAC(3) en-zymes] have been classified into several groups based on dif-ferences in the spectrum of aminoglycosides they modify, they fall into only two groups based on the relationships betwee