Resistance to Linezolid: Characterization of Mutations in rRNA and Comparison of Their Occurrences in Vancomycin-Resistant Enterococci

Abstract

To assess the potential for emergence of resistance during the use of linezolid, we tested 10 clinical isolates of vancomycin-resistant enterococci (VRE) (four Enterococcus faecalis, five Enterococcus faecium, and one Enterococcus gallinarum) as well as a vancomycin-susceptible control (ATCC 29212) strain of E. faecalis. The enterococci were exposed to doubling dilutions of linezolid for 12 passes. After the final passage, the linezolid plate growing VRE contained a higher drug concentration with E. faecalis than with E. faecium. DNA sequencing of the 23S rRNA genes revealed that linezolid resistance in three E. faecalis isolates was associated with a guanine to uracil transversion at bp 2576, while the one E. faecium isolate for which the MIC was 16 g/ml contained a guanine to adenine transition at bp 2505.

Linezolid: The First Oxazolidinone Antimicrobial

“…It appears to be more difficult to generate mutants of Enterococcus faecium resistant to linezolid than for quinupristin-dalfopristin (22). The specific point mutations causing resistance in Staphylococcus aureus, Enterococcus faecalis, Enterococcus faecium, and other organisms have been mapped to several different locations in domain V of the 23S ribosomal RNA of the 50S subunit of the ribosome (23)(24)(25), and studies in resistant clinical isolates reveal similar mutations (26 -28; Moellering RC Jr., Tsiodras S, Gold H, Meka V, Sakoulas G, Eliopoulos GM, et al Unpublished data). Resistance to the oxazolidinones based on inactivation has not been demonstrated in any bacterial species tested.…”

Genetic modifications to temperate Enterococcus faecalis phage ϕEf11 that abolish the establishment of lysogeny and sensitivity to repressor, and increase host range and productivity of lytic infection

“…In terms of oral disease, E. faecalis is the most commonly isolated species from infected root canals of teeth that fail to heal following root canal therapy (Sundqvist et al, 1998;Peciuliene et al, 2000;Pinheiro et al, 2003 Complicating management of these infections is the development of resistance among many enterococcal strains against many of the available, previously effective antibiotics, including vancomycin (Havard et al, 1959;Murray & Mederski-Samaroj, 1983;Uttley et al, 1988;Grayson et al, 1991;Bonten et al, 2001;Tenover & McDonald, 2005). Although a modest number of new antibiotics, such as linezolid and daptomycin, have been developed to provide treatment alternatives in cases of infection by organisms that are resistant to all previously available antibiotics, there have been numerous reports of resistance by E. faecalis and E. faecium strains to these antibiotics as well (Eliopoulos et al, 1998;Prystowsky et al, 2001;Gonzales et al, 2001;Herrero et al, 2002;Johnson et al, 2004;Munoz-Price et al, 2005;Kanafani et al, 2007;Hidron et al, 2008;Marshall et al, 2009;Kelesidis et al, 2011;Ross et al, 2011;Ntokou et al, 2012). Therefore, alternative approaches to manage these infections should be explored.…”

Clinical and Microbiological Aspects of Linezolid Resistance Mediated by the cfr Gene Encoding a 23S rRNA Methyltransferase

“…Another mutation (T2500A) was characterized in a single patient bloodstream isolate of MRSA (17). Some additional mutations that have been found solely in vitro include the following: G2447T in S. aureus and G2505A, G2512T, G2513T, and C2610G in enterococci (20,31). Most bacteria possess multiple copies of the 23S rRNA gene, with strains of S. aureus having five or six rRNA operons.…”