Evolution of aminoglycoside resistance phenotypes of four Gram-negative bacteria: an 8-year survey in a University Hospital in Greece.

In order to determine the resistance patterns and evolution trends of four common Enterobacteriaceae (Escherichia coli, Proteus spp., Klebsiella spp. and Enterobacter spp.), aminoglycoside resistance phenotypes of 8917 non-repetitive strains, isolated over an 8-year period, were analysed. Phenotypes were defined by examining the susceptibility of the strains to a panel of aminoglycosides, using disk diffusion method. A large diversity of different resistance phenotypes was encountered. A significant progressive increase in the proportions of wild-type E. coli strains was noted. Among resistant strains of Enterobacter spp. and Klebsiella spp., the incidence of phenotype KTANt (kanamycin, tobramycin, amikacin and netilmicin), indicative of AAC(6')-I production, was very high (66.7 and 46.5%, respectively). Phenotypes indicative for gentamicin-modifying enzymes as well as broad-spectrum combinations (combinations of gentamicin-modifying enzymes with AAC(6')-I) were infrequent.