Increasing prevalence of high-level gentamicin resistant enterococci: An emerging clinical problem

Abstract

Enterococci have recently been recognized as a causative organism of intractable infections. This study investigated the species prevalence, antimicrobial resistance and characterization of high-level gentamicin resistant (HLGR) enterococci. A total of 163 enterococci were isolated from various clinical samples collected from hospitalized patients in Riyadh, Saudi Arabia. The Enterococcus faecalis was the most frequent species (58.9%), followed by Enterococcus faecium (26.9%), Enterococcus avium(6.1%), Enterococcus gallinarum (2.5%), Enterococcus durans (1.8%), Enterococcus hirae (1.2%), Enterococcus casseliflavus (1.2%) and Enterococcus cecorum (0.6%). High-level of resistances to gentamicin and streptomycin were detected by the disc diffusion method, in 20.2% of isolates. The prevalence of resistances among β-lactam antibiotics and glycopeptides were very low. All Enterococcus isolates were identified phenotypically by conventional methods and genotypically by polymerase chain reaction (PCR) targeting aminoglycoside modifying enzyme (AMEs) genes including aac(6`)-Ie-aph(2``)-Ia, aph(2``)-Ib, aph(2``)-Ic, aph(2``)-Id, aph(3`)-IIIa and ant(4`)-Ia. The genetic diversity of E. faecalis presenting HLGR was assessed by pulsed-field gel electrophoresis (PFGE) of chromosomal deoxyribonucleic acid (DNA) after SmaI digestion. Most of the high level aminoglycoside resistant isolates contained genes coding for the bifunctional AMEs AAC(6`)-APH(2``), ANT(6`) and APH(3`) but not the ANT(4`). The results demonstrated that the spread of the aac(6`)-Ie-aph(2``)-Ia gene was responsible for HLGR among enterococci isolated in Riyadh hospital. Key words: Enterococci, resistance, Enterococcus faecalis, high-level gentamicin resistant (HLGR).