Aminoglycosides modifying enzymes genes among the population of enterococci in Tehran

ABSTRACT

Resistance to high level concentration of gentamicin is widespread among isolates of enterococci at Tehran Hospitals. To understand the mechanism of resistance among the Iranian isolates, we screened a collection of E. faecalis and E. faecium isolates to detect aminoglycoside modifying enzymes genes. To detect the high level gentamicin resistant isolates of enterococci [HLGR phenotype, MIC>500 microg/ml], 114 clinical isolates of E.faecalis [n=79] and E. faecium [n=35] were tested with disks containing 120 microg of gentamicin. The macrobroth dilution assay was then used to determine the minimum inhibitory concentration of gentamicin. The susceptibility of isolates against amikacin, netilmicin, tobramycin, kanamycin were also determined by Kirby-Bauer method. All isolates were subjected to polymerase chain reaction assays targeting aminoglycoside modifying enzyme [AMEs] genes including aac [6']-aph [2"], aph [2"]-Ib, aph [2"]-Ic, aph [2"]-Ia, aph [2"]-Id. Aph[3']-IIIa and ant [4']-Ia. All isolates with HLGR phenotype and those showing 64phenotypes and those with MIC<500 in respects. Co-existence of aac [6']-aph [2"] and aph [3']-IIIa gene among HLGR isolates of E. faeclais and E. faecium were 59.5% and 64.7% respectively. The gene aph [2"]-Ic was amplified in two isolates of E. faecium. The results of PCR for aph [2"]-Id, ant [4']-Ia and aph [2"]-Ib genes were negative. The aac [6']-aph [2"] was the most frequent gene encoding resistance to gentamicin and other aminoglycosides followed by aph[3']-IIIa. Isolates lacking these genes were susceptible to all aminoglyocosides used in this study