Molecular Characterization of High-Level Aminoglycoside Resistance among Enterococcus Species

Abstract

Background Enterococci are nosocomial pathogen. They can develop high-level resistance to aminoglycoside by producing aminoglycoside modifying enzymes (AMEs). In enterococci, high level resistance to aminoglycosides is mediated by acquisition of plasmid mediated genes encoding for aminoglycoside modifying enzymes (AMEs). High level gentamicin resistance (MIC ≥ 500μg /mL) is predominantly mediated by aac(6′)-Ie-aph(2″)-Ia, encoding the bifunctional aminoglycoside modifying enzyme AAC(6′)-APH(2″). This enzyme eliminates the synergistic activity of gentamicin when combined with a cell wall active agent. Other AME genes such as aph(2″)-Ib, aph(2″)-Ic, aph(2″)-Id and ant(4′)-1a have also been detected in enterococci. Objective This study was carried out to determine the diverse prevalence of AME and their pattern of occurrence in the clinical isolates of Enterococci. Materials and Methods A total number of 150 clinical isolates were included in this study. Susceptibility to various antibiotics was determined by disc diffusion. Minimum Inhibitory Concentration (MIC) was ascertained by agar dilution method. Polymerase chain reaction was done to screen the following AMEs (aac(6′)-Ie-aph(2″)-Ia; aph(2″)-Ib; aph(2″)-Ic; aph(2″)-Id and aph(3′)- IIIa genes). Results 51.3% of the study isolates exhibited high level gentamicin resistance. Polymerase chain reaction revealed that aph(3′)-111a is the most prevalent AME, followed by aac(6′)-1e-aph(2″)-1a. The combination of both the genes were detected in 44.1% of the study isolates. The rest of the AMEs and their combinations were not encountered in this study. 8.6% of the study isolates did not harbour any AME genes screened for, but was phenotypically resistant to gentamicin. In contrast 31.3% anchored the AME genes but phenotypically appeared susceptible to gentamicin. Conclusion This study indicates the high- level aminoglycoside resistance disseminated among Enterococci in our geographical region. It also emphasizes the detection of AMEs by PCR is mandatory because strains that appear susceptible by disc diffusion and/or MIC method may harbour one or more AMEs genes leading to therapeutic failure.

Alpha-Naphthoflavone as a Novel Scaffold for the Design of Potential Inhibitors of the APH(3’)-IIIa Nucleotide-Binding Site of Enterococcus faecalis

“…Although part of the human gastrointestinal microbiota, this species has become a constant threat, especially to hospitalized patients because of the risk of developing bacteremia, endocarditis, and urinary tract and intra-abdominal infections [ 4 , 5 , 6 ]. The limited susceptibility of enterococci to antibiotics is due to both intrinsic and extrinsic resistance mechanisms [ 7 , 8 ]. The intrinsic mechanisms are mainly linked to the widespread utilization of aminoglycosides, cephalosporins, clindamycin, sulfamethoxazole, and trimethoprim antibiotics [ 8 ].…”

“…The limited susceptibility of enterococci to antibiotics is due to both intrinsic and extrinsic resistance mechanisms [ 7 , 8 ]. The intrinsic mechanisms are mainly linked to the widespread utilization of aminoglycosides, cephalosporins, clindamycin, sulfamethoxazole, and trimethoprim antibiotics [ 8 ]. Conversely, the extrinsic resistance mechanisms arise from the acquisition of vancomycin, ampicillin, and aminoglycoside resistance genes or mutations through horizontal transfer in enterococci [ 8 , 9 ].…”

Natural products as Potential Inhibitors of APH(3')-IIIa of <em>Enterococcus faecalis</em>: An <em>In-silico</em> Perspective

“…This potential gives this bacterium a selective advantage over other species that share the same environment, thus allowing it to spread further than others [4,5]. Therefore, although E. faecalis is part of the normal human microbiota it can become opportunistic, in this condition it is the most prevalent species of the genus Enterococcus in the total infection events, with approximately 80-90% of cases [6,7]. The most common community infections caused by this species are infective endocarditis, gastrointestinal and urinary infections [8].…”

“…On the other hand, sepsis, meningitis, and catheterization procedures, especially in intensive care settings, are some of the causes of nosocomial complications [4,5,9]. Furthermore, the high number of these conditions is due to E. faecalis exhibiting an intrinsic resistance to many antibiotics, among them the aminoglycosides [7,10].…”

“…This class is in turn divided into seven types called APH(3')-I to APH(3')-VII [15]. Assessments of different clinical isolates of E. faecalis in several countries have shown that the phenotype of resistance to aminoglycosides expressing the aph(3')-IIIa gene is mainly due to the extended use of amikacin, kanamycin and streptomycin [7,[16][17][18]. Knowing a long time that research and development of new antibiotics takes, one option is to find adjuvants that can be associated with them to restore their efficacy [19].…”