Linezolid resistance in vancomycin resistant enterococci: a worrisome situation

Vancomycin resistant enterococci (VRE) have emerged as important nosocomial pathogens since 1986. VRE have been associated with higher morbidity and mortality rates than vancomycin susceptible enterococci. Of over 50 species of Enterococcus, a genus of Gram-positive cocci arranged in pairs and short chains, E. faecalis is the most common cause of infections whereas E. faecium is the species exhibiting highest rate of antibiotic resistance. VRE have been implicated in varieties of infections such as bacteremia, infective endocarditis, intra-abdominal and pelvic infections, urinary tract infections, central nervous system infections and skin and skin structure infections. Since VRE exhibit multidrug resistance, there are very limited options for treatment of infections caused by them. One of the major treatment options is linezolid. The drug is the first member of oxazolidinones that received Food and Drug Administration (FDA) approval in 2000 as the last-resort drug for treatment of serious Gram-positive bacterial infections, including vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA) and multi-drug resistant Streptococcus pneumoniae infections. This bacteriostatic drug binds to rRNAs of both the 30S and 50S ribosomal subunits, inhibits formation of initiation complex and prevents the synthesis of bacterial protein. Though this drug has been very useful to treat serious infections caused by VRE, some strains of enterococci have already been found to exhibit resistance to this drug.