Study of aac(6')Ie-aph(2?)Ia Gene in Clinical Strain of Enterococci and Identification of High-Level Gentamicin Resistante Enterococci

Introduction &

Enterococci have emerged as the leading nosocomial pathogens. In addition to natural resistance to many agents، enterococci have also developed plasmid- and transposon-mediated resistance to high concentrations of aminoglycosides. High-level gentamicin resistance (HLGR) of enterococci results in the failure of drug synergism with an aminoglycoside plus cell-wall-active agents. HLGR (MIC=500μg/ml) strains is usually due to the presence of the aac (6'') Ie-aph (2″) Ia gene.

In the present experimental study 142 enterococci were isolated from the patients’ species. Identification was done by using standard methods and antimicrobial susceptibility test was performed by disc diffusion technique. MIC of Gentamicin was determined by a broth micro dilution method (NCCLS). PCR was performed to detect the aac (6'') Ie-aph (2″) Ia gene. Presence of the gene aac (6'') -Ie-aph (2″) -Ia was confirmed by digest with Sca1 enzyme. A PCR product was sequenced and BLAST analyzed at the NCBI database to be confirmed.

62 (43. 7%) out of the 142 isolates، were found to exhibit HLGR phenotype. MIC ranging from 512 to >1024 μg/ml in 55 HLGR isolates. All resistant isolates except one، were found to harbor the aac (6'') Ie-aph (2″) Ia gene. In our strain collection، 42% of E. faecalis and 44% of E. faecium were HLGR. In the HLGR isolates the prevalence of resistance to other antibiotics and Multi Drug Resistance (MDR) was higher than non–HLGR. This prevalence in E. faecium was higher than E. faecalis. The sequence was compared with a published sequence and confirmed.

Our results indicate that high prevalence of MDR and HLGR enterococcal colonization is an important problem in our medical centers. Spread of the aac (6'') -Ie-aph (2″) -Ia gene was responsible for HLGR among enterococci isolated from the patients in Tehran.