Aminoglycoside-modifying enzymes associated with hospital isolates of Gram-negative rods.

Multi-resistant Enterobacteriaceae and Pseudomonas isolated from clinical specimens at RNS were characterized for resistance phenotype and transferred resistant phenotype. These isolates were obtained over a two year period from different specimens and from patients with varying clinical syndromes. Twenty-six of these isolates were further characterized with respect to their aminoglycoside modifying enzymes. Only three enzymes were detected: AAC(3)-I, APH(3')-I and AAD(2")-II. The substrate range of these enzymes was investigated and not always found to coincide with the transferred phenotype. AAD(2")-II was found only in association with APH(3')-I and not alone. The substrate range of AAC(3)-I from Pseudomonas was different from AAC(3)-I from Enterobacteriaceae but not sufficiently dissimilar to classify them as separate isoenzymes. The relatively few aminoglycoside-inactivating enzymes suggest that within this hospital there may be a limited gene pool for these enzymes.