Relation between aminoglycoside 2"-O-nucleotidyltransferase activity and aminoglycoside resistance.

The relationship between plasmid-coded aminoglycoside 2"-O-nucleotidyltransferase [ANT(2")] activity and the minimum inhibitory concentration for aminoglycosides was studied. ANT(2") was very unstable, and therefore, procedures for handling this enzyme were optimized. Escherichia coli L58058.1 producing ANT(2") was resistant to gentamicin, sisomicin, kanamycin, tobramycin, and dibekacin but susceptible to netilmicin, amikacin, and neomycin. However, only amikacin and neomycin were not modified by ANT(2"). A correlation between the substrate profile of the enzyme tested at 0.15 mM and the minimum inhibitory concentrations of the aminoglycosides could not be demonstrated. The substrate concentration-dependent enzyme activity curves proved to be a better alternative than a substrate profile based on tests at one concentration. At concentrations of greater than 10(-2) mM, ANT(2") demonstrated substrate inhibition that explains the discrepancy between ANT(2") activity and the minimum inhibitory concentrations. A close correlation was found between the physiological efficiency (Vmax/Km ratio) of ANT(2") and the minimum inhibitory concentrations for the enzyme-producing strain.