Tobramycin adenylyltransferase: a new aminoglycoside-inactivating enzyme from Staphylococcus epidermidis.

Certain strains of Staphylococcus epidermidis resistant to the aminoglycoside antibiotics were shown to contain an enzyme that inactivates the kanamycins, neomycins, butirosins, paromomycin, gentamicin A, amikacin, and tobramycin by adenylylation. Tobramycin adenylyltransferase, as this enzyme is called, was found to be optimally active at pH 5.5. With paromomycin or neomycin B and C as substrates, however, two pH values (5.5 and 9.0) for optimal activity were observed. The enzyme requires Mg++ for activity and is stabilized significantly by dithiothreitol. It is probable that the 4'-hydroxyl group of ring I of the antibiotics is adenylylated. Those aminoglycosides that are not substrates for the enzyme lack a hydroxyl group in the corresponding position.