A spontaneous point mutation i the aac(6')-lb' gene results in altered substrate specificity of aminoglycoside 6'-N-acetyltransferase of a Pseudomonas fluorescens strain

Abstract The aac(6')-lb' gene from Pseudomonas fluorescens BM2687, encoding an aminoglycoside 6'- N -acetyltransferase type II which confers resistance to gentamicin but not to amikacin, was characterized. Nucleotide sequence determination indicated total identity between aac6')-lb and the aac(6')-lb gene from Pseudomonas aeruginosa BM2656 1] with the exception of a C-to-T transition that results in a serine to lecine substitution at position 83 of the deduced polypeptide. The aac(6')-lb gene specifies a type I enzyme which confers resistance to amikacin but not to gentamicin 2]. It thus appears that the point mutation detected is responsible for enzymic altered substrate specificity.