High-Level Resistance to Aminoglycosides Among Multidrug Resistant Non-faecalis and Non-faecium Enterococci.

BACKGROUND

Enterococci are considered as important causative pathogens of a variety of community and hospital-acquired infections. Due to the development of multidrug resistant (MDR) enterococci and the emergence of strains possessing high-level resistance to antimicrobial agents, treatment of their infections has been more complicated. In addition to more prevalent species of the Enterococcus genus, non-faecalis/non-faecium species are also responsible for severe healthcare-associated infections. Therefore, this study was designed to investigate high-level gentamicin resistance among the clinical isolates of non-faecalis and non-faecium enterococci in Shiraz, in the southwest of Iran.

METHODS

A total of 28 non-faecalis/non-faecium spp. were isolated from various infections. They were identified by the conventional methods. Antimicrobial resistance patterns, multidrug resistance, and high-level gentamicin resistance were determined, according to CLSI guidelines and related definitions. Detection of aminoglycoside resistance genes was also performed using standard procedures.

RESULTS

All of the isolates were MDR (100%), and 75% of them were high-level gentamicin resistant (HLGR) (MIC ≥ 500 μg/mL). The distributions of aac(6')-Ie-aph(2'')-Ia and aph(3')-IIIa resistance genes were 82.1% and 75%, respectively. The aph(2")-Ib, aph(2")-Ic, aph(2")-Id, and ant(4')-Ia genes were not found in any isolate. Although vancomycin resistance was observed in 19 (67.8%) isolates, all of the isolates were susceptible to linezolid and fosfomycin.

CONCLUSIONS

Our data indicate a high rate of MDR non-faecalis/non-faecium isolates. Furthermore, high-level gentamicin resistance was notable and all of the HLGR isolates harbored at least one of aac(6')-Ie-aph(2'')-Ia or aph(3')-IIIa resistance gene.