Mechanism of Drug Resistance in Enterococci and Therapeutic Options - A Review

Abstract

Enterococci exhibit an array of ways for constitutional and extrinsic resistance to primary antimicrobial agents available for clinical use. Susceptibility of these agents to β lactams, aminoglycosides or glycopeptides antibiotics or low susceptibility to combination of these agents, monomicrobial or polymicrobial nature of the infection, the involvement of heart valves or other endovascular structures affects therapy of Enterococcal infection. Vancomycin-resistant phenotypes A and B are most prevalent among medically important Enterococci isolates. Due to poor uptake of aminoglycosides, moderate level inherent resistance was reported in Enterococci. Gentamicin and Streptomycin are among the aminoglycoside antibiotics recommended for synergistic combination therapy with a cell wall acting agent. Enterococci isolates display inherent resistance to beta-lactam antibiotics due to less affinity penicillin-binding proteins, class B. Resistance to macrolides, due to erm B genotype and efflux proteins are common in Enterococci. Fluoroquinolone resistance due to genetic changes in chromosomal resistance determining regions has been observed in Enterococci isolates. Despite studies on good invitro action of Daptomycin, Linezolid and Tigecycline on Enterococci, their use may be limited due to shortage of clinical data and emergence of drug resistance. Thus optimal therapeutic option for Multidrug-resistant Enterococci infection is based on empirical observation, higher doses and combination therapies. This article reviews the antimicrobial resistance mechanism in Enterococci and available therapeutic options.