Diversidade e estrutura populacional de Enterococcus faecalis resistentes a níveis elevados de aminoglicosídeos

Abstract

Enterococcus faecalis stands out for the high percentage of isolates associated with more serious clinical conditions such bloodstream infections. The aim of this study was to evaluate E. faecalis isolates showing high-level aminoglycosides resistance (HLAR), as their phenotypes and genotypes of antimicrobial resistance, virulence traits and population diversity. A total of 306 bacterial E. faecalis HLAR strains isolated from patients attended at hospital institutions located in the State of Rio de Janeiro, during the period of Jan/Jan 2005/2013 were selected. Susceptibilities profiles have been assessed by disk diffusion to 14 antimicrobials, and the minimum inhibitory concentration for gentamicin (GEN) and streptomycin (EST) was determined by agar dilution. Genes associated to the characteristics of HLAR and to virulence were identified by PCR assay. Analysis of genotypic diversity and population structure were carried out by pulsed-field electrophoresis (PFGE) and multiple loci sequencing typing (MLST). Among the isolates showing high-level gentamicin resistance (HLR-G), the gene aac(6')-Ie-aph (2 ")Ia was prevalent followed by aph (2)-lc. Moreover, among HLR to streptomycin isolates (HLR-S), the gene ant6´-Ia was the prevalent. Vancomycin resistant E. faecalis (VREfa) showed high rates of resistance to the 14 antimicrobials tested. Among the 42 VREfa isolates, 38 and four isolates harbored vanA and vanB genotypes, respectively. The genes efaA, eep, gelE, ace, asa1 and agg have been identified in almost all of the samples, and a moderate frequency was observed for cyl the esp gene. The gene hyl was not detected from these E. faecalis HLAR isolates. The PFGE analysis resulted in the identification of 36 groups, being GP8, GP3 and GP5 the prevalent among HLR-G isolates; GP1, GP8, GP16, GP3 and GP19 among HLR-GS; and GP22, GP2 and GP24 among HLR-S. The MLST analysis revealed 17 STs besides two new STs that were described in this study (ST769 and ST770). The ST6, ST21, ST4 and new ST769 were the most frequent. VRE samples were related to ST6, ST9, ST97, ST103 and to the new ST769. Genes eep and efa were associated with all STs; however cyl was correlated to the CC2 (ST6 and ST2), esp to ST21, ST26 and ST40; gelE to CC2, CC21, CC388, CC30, ST4, ST9, ST40, ST97 and ST330; asa1 to mapped to CC2, CC388, ST4, ST9, ST26, ST55, ST97, ST21 and ST330; agg to CC2, CC388, ST4, ST9, ST26, ST55, ST97 and ST330; and ace to CC2, CC388, ST4, ST9, ST26, ST55, ST97 and ST330. E. faecalis HLRA high-risk clones have been described worldwide and the clonal expansion of some of these lineages that included resistance to vancomycin and penicillin including the presence of virulence , highlights the attention to the emergence of more adapted and potentially pathogenic clones in the hospital environment.