Aminoglycoside resistance among Enterobacteriaceae and Acinetobacter species

Abstract

Aminoglycoside-resistant isolates of Enterobacteriaceae and Acinetobacter have been examined for the presence of aminoglycoside-inactivating enzymes. Of 78 strains resistant or moderately resistant to gentamicin (with minimum inhibitory concentrations of 4 mg/l or more) 64 produced inactivating enzymes. Aminoglycoside 2′-N-acetyltransferase, which was produced by 33 gentamicin-resistant strains of Providencia stuartii and 3 of Proteus rettgeri, was found most frequently. This enzyme was also produced by two strains of Prov. stuartii and one strain of P. rettgeri that were not resistant to gentamicin. Aminoglycoside 3-N-acetyltransferase I was produced by 25 gentamicin-resistant strains of other species of Enterobacteriaceae. One strain of Klebsiella aerogenes produced aminoglycoside 2″-O-nucleotidyltransferase. Five strains of Acinetobacter spp. and 3 of Serratia marcescens that were resistant to tobramycin produced aminoglycoside 6′-N-acetyl-transferase. Gentamicin-inactivating enzymes were not detected in 7 gentamicin-resistant strains of Escherichia coli, 4 of K. aerogenes, 2 of Proteus mirabilis and 1 of Citrobacter koseri. Streptomycin phosphotransferase or streptomycin adenylyltransferase was found in streptomycin-resistant strains of species other than Prov. stuartii. Aminoglycoside 3′-O-phosphotransferase was found in strains resistant to kanamycin and neomycin. The patterns of cross-resistance between pairs of aminoglycosides could often be explained by the substrate profile associated with predominant mechanisms of resistance, as could the degrees of correlation between minimum inhibitory concentrations of pairs of aminoglycosides.