Enzymatic modification of aminoglycoside antibiotics in gentamicin-resistant gram-negative bacteria.

An in vitro evaluation of 32 gentamicin-resistant, Gram-negative bacteria from hygiene-centres in Berne, Switzerland and Bratislava, Czechoslovakia, revealed that 24 strains produced gentamicin-modifying enzymes. Occurrence of acetyltransferases (AAC) was confirmed in 16 strains, adenylyltransferase (AAD) /2''/ was observed in 13 strains while 5 of the gentamicin-resistant strains produced both enzymes. All Czechoslovak strains were amikacin-susceptible, in amikacin-resistant Pseudomonas aeruginosa strains from Switzerland the presence of AAC/6'/ was found. In the majority of gentamicin-resistant, netilmicin-susceptible strains the occurrence of AAD/2''/ was observed. Gentamicin-resistance in the modifying enzymes producing strains was due either to production of an acetyltransferase or the adenylyltransferase except Swiss strains of Serratia marcescens where a simultaneous production of both types of the enzymes was noted. Twenty eight strains produced an enzyme modifying aminoglycosides of any kind.