Correlation of aminoglycoside resistance with the KmS and Vmax/Km ratios of enzymatic modification of aminoglycosides by 2''-O-nucleotidyltransferase

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Abstract
A clinical isolate, Serratia marcescens 75, was found to be susceptible to netilmicin and yet had a high level of aminoglycoside 2''-O-nucleotidyltransferase activity for netilmicin. Kinetic studies of the partially purified enzyme revealed substrate inhibition for gentamicin and tobramycin at concentrations greater than 10(-2) mM, but this was not observed for netilmicin. The MICs of the aminoglycosides tested exhibited a good inverse correlation with the Km values for the enzyme and a direct correlation with the Vmax/Km ratios of the enzyme.