AMINOGLYCOSIDE RESISTANCE MECHANISMS IN ENTEROBACTERIACEAE AND PSEUDOMONAS SPP FROM 2 DANISH HOSPITALS - CORRELATION WITH TYPE OF AMINOGLYCOSIDE USED

Sixty-two aminoglycoside-resistant Gram-negative enteric bacteria were isolated over a 3-year period from two hospitals (Bispebjerg and Esbj erg) among a total of almost 270,000 isolates. These hospitals were se lected because of their different aminoglycoside policies during the y ears investigated. At Bispebjerg Hospital the principal aminoglycoside used was tobramycin, while gentamicin was the first choice at Esbjerg Hospital. Escherichia coli was the most frequently found aminoglycosi de-resistant species. Among the 61 aminoglycoside-resistant strains st udied, resistance was due to aminoglycoside-modifying enzymes in all e xcept two Xanthomonas maltophilia strains. The ANT(2'') enzyme occurre d significantly more often at Esbjerg Hospital (p=0.001), while enzyme s of the AAC(3) or AAC(6') moieties were more common, but not signific antly so, at Bispebjerg Hospital. The phenotypic pattern of aminoglyco side resistance, as determined by disc diffusion, correlated 100% with the ANT(2'') and AAC(3)-V (the two most common enzymes among the isol ates) genotype of the organisms as established using DNA probes. Media n minimum inhibitory concentrations (MICs) (mg/l) for clinically utili zed aminoglycosides were: amikacin (1.6), gentamicin (25.0), kanamycin (50.0), netilmicin (1.6-25.0) and tobramycin (12.5-50.0). Isolates fr om Bispebjerg Hospital revealed significantly higher MICs for netilmic in and tobramycin (p<0.01) as compared to isolates from Esbjerg Hospit al.