Patterns and distribution of aminoglycoside-acetylating enzymes in rapidly growing mycobacteria

Cell-free extracts from clinical, laboratory, and environmental isolates of Mycobacterium fortuitum, Mycobacterium smegmatis, Mycobacterium phlei, and Mycobacterium vaccae were tested for the presence of aminoglycoside-acetylating enzyme and compared with enzymes from gram-negative organisms. Acetylating activity was detected in all strains examined despite variable levels of aminoglycoside susceptibility. Substrate profiles revealed 2 different patterns of 3-N-acetyltransferase. One pattern exhibited broad substrate specificity including significant activity to fortimicin and was specific for Mycobacterium fortuitum strains, whereas the second pattern showed a much narrower substrate range and was observed for the other 3 environmental species. Both types of enzymes inactivated the antimicrobial activity of drug in vitro. The acetylation reaction of mycobacterial enzyme with radiolabeled acetyl coenzyme A was significantly inhibited by malonyl- (34.7%), propionyl- (21.3%), and butyryl- (12.5%) coenzyme A in the presence of adenosine-5'-triphosphate, whereas no inhibition could be observed for the type enzyme (3-N-acetyltransferase-III) from Pseudomonas aeruginosa suggesting the two enzymes are different. Thus all species of rapidly growing mycobacteria probably contain one of several different types of aminoglycoside acetyltransferases including some isolates and species without a resistance phenotype. The origin and specific function of these enzymes are not known.