CLONING AND CHARACTERIZATION OF A 3-N-AMINOGLYCOSIDE ACETYLTRANSFERASE GENE, AAC(3)-IB, FROM PSEUDOMONAS-AERUGINOSA

A novel gene encoding an aminoglycoside 3-N-acetyltransferase, which c onfers resistance to gentamicin, astromicin, and sisomicin, was cloned from Pseudomonas aeruginosa Stone 130. Its sequence was determined an d found to show considerable similarity to an aac(3)-I gene previously cloned from R plasmids from Enterobacter, Pseudomonas, and Serratia s pp. We have designated the genes from the R plasmids and this work aac (3)-Ia and aac(3)-Ib, respectively, The two aac(3)-I genes share 74% n ucleotide identity, and their deduced protein products are 88% similar . These data suggest that the genes derive from a common ancestor. Hom ology between the flanking sequences of both dac(3)-I genes and other resistance determinants known to reside in integron environments was a lso observed. Intragenic probes specific for either aac(3)-Ia or aac(3 )-Ib were used in hybridization studies with a series of gentamicin-, astromicin-, and sisomicin-resistant clinical isolates. Of 59 clinical isolates tested, no isolates hybridized with both probes, 30 (51%) hy bridized with the aac(3)-Ia probe, 12 (20%) hybridized with the aac(3) -Ib probe, and 17 (29%) did not hybridize with either probe. These dat a suggest the existence of at least one other aac(3)-I gene.