PH MODULATION OF AMINOGLYCOSIDE RESISTANCE IN STAPHYLOCOCCUS-EPIDERMIDIS HARBORING 6'-N-AMINOGLYCOSIDE ACETYLTRANSFERASE

The kinetic constants of the aminoglycoside-modifying enzyme 6'-N-amin oglycoside acetyltransferase (AAC(6')IV) from the clinical strain Stap hylococcus epidermidis RYC 13036 differed depending on whether tobramy cin and amikacin (glucosamine group) or gentamicin and netilmicin (gar osamine group) were used as substrates. Acetylation of the glucosamine antibiotics was highly susceptible to substrate inhibition which incr eased with pH whereas the garosamine group compounds showed limited su bstrate inhibition over a wide pH range. These differences in activity correlated with MIC values of S. epidermidis RYC 13036 for different aminoglycosides. Aminosugars moiety and pH markedly influenced the AAC (6')IV-aminoglycoside interactions.