Clonal dissemination of high-level gentamicin-resistant isolates of Enterococcus faecalis within a university hospital in southeastern Iran

Combination of a cell wall-active antibiotic with an aminoglycoside confers a synergistic effect in the treatment of some severe enterococcal infections. Unfortunately, with the emergence of enterococci with high-level resistance to aminoglycosides, particularly to gentamicin, the efficacy of the synergistic combinations has decreased. In this study, high-level gentamicin-resistant (HLGR) isolates of enterococci and the diversity of the genes encoding aminoglycoside-modifying enzymes (AMEs) as well as putative clonal dissemination of HLGR isolates were investigated in a university hospital in southeastern Iran.

The minimum inhibitory concentration of gentamicin was determined and HLGR isolates were investigated for AME genes. Genetic similarity between isolates was analyzed using repetitive extragenic palindromic (rep)-Polymerase Chain Reaction (PCR) assay.

Of 150 Enterococcus isolates, 62 isolates including Enterococcus faecalis (n = 46) and E. faecium (n = 16) were identified as HLGR. The most prevalent AME genes in both species were as follows: aph(3^′)-IIIa (n = 44), aac(6^′)-Ie-aph(2^′)-Ia (n = 36), and ant(4^′)-Ia (n = 15). The rep-PCR analysis showed clonality among E. faecalis isolates, so that 27 isolates were grouped in seven clusters representing similarity greater than 95%.