ANALYSIS OF NEOMYCIN, KANAMYCIN, TOBRAMYCIN AND AMIKACIN RESISTANCE MECHANISMS IN GENTAMICIN-RESISTANT ISOLATES OF ENTEROBACTERIACEAE

Twenty-four gentamicin-resistant isolates of Enterobacteriaceae, obtai ned from the clinical laboratories of three health centres in Nablus, Palestine, were tested for susceptibility to neomycin, kanamycin, tobr amycin and amikacin, Resistance rates were 29.2% for neomycin, 58.3% f or kanamycin, 45.8% for tobramycin and 8.3% for amikacin, Fourteen (58 .3%) isolates were noted to be multiresistant, i,e,, resistant to gent amicin and two or more other aminoglycosides; resistance to gentamicin , kanamycin and tobramycin was the most common pattern of multiple res istance. This pattern implies the involvement of adenyltransferase ANT (2 '')-I activity. Plasmid profiles and curing experiments suggested a plasmid localisation of gentamicin, neomycin, kanamycin and tobramyci n resistance genes. However, a chromosomal location is proposed for pl asmid-deficient strains, Cross-resistance in two isolates to all amino glycosides tested suggested membrane impermeability to aminoglycosides as the mechanism of resistance.