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Role of a qnr-like gene in the intrinsic resistance of Enterococcus faecalis to fluoroquinolones.

ABSTRACT: Fluoroquinolones are poorly active against enterococci. Recently, plasmid-borne resistance to fluoroquinolones due to the qnr gene was reported in members of the Enterobacteriaceae family. The gene encodes a pentapeptide repeat protein that protects DNA gyrase from inhibition by fluoroquinolones. We have identified in the genome of Enterococcus faecalis V583 a qnr-like gene, named E. faecalis qnr (qnr(E. faecalis)), encoding a putative pentapeptide repeat protein that shares 25% identity with Qnr. To assess its potential role in the intrinsic resistance of E. faecalis to fluoroquinolones, qnr(E. faecalis) was inactivated in E. faecalis JH2-2 by insertion of the thermosensitive vector pG1KT. This strain was then complemented with qnr(E. faecalis) cloned in the multicopy plasmid pORI23. The effects of its overexpression were also studied. Inactivation of the qnr(E. faecalis) gene resulted in twofold decreases in the MICs of ofloxacin and ciprofloxacin. When the gene was complemented or overexpressed, MICs of fluoroquinolones increased four- to nine-fold, leading to MICs of ofloxacin and ciprofloxacin equal to 32 mug/ml and 8 mug/ml, respectively. The E. faecalis Qnr (Qnr(E. faecalis)) protein was produced and purified. Qnr(E. faecalis) protein protected Escherichia coli DNA gyrase from inhibition by ofloxacin. The qnr(E. faecalis) gene was then introduced into E. coli DH10B, Staphylococcus aureus RN4220, and Lactococcus lactis IL-1419 to study its heterologous expression. MICs of the various fluoroquinolones tested increased 4- to 16-fold, showing that Qnr(E. faecalis) conferred resistance to fluoroquinolones in various bacterial backgrounds. Overexpression of qnr(E. faecalis) in enterococci or mobilization of the gene to other bacterial species may be anticipated as a possible new mechanism for fluoroquinolone resistance.

SUBMITTER: Arsene S

PROVIDER: S-EPMC2043171 | biostudies-literature | 2007 Sep

REPOSITORIES: biostudies-literature

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Role of a qnr-like gene in the intrinsic resistance of Enterococcus faecalis to fluoroquinolones.

Arsène Stéphanie S Leclercq Roland R

Antimicrobial agents and chemotherapy 20070709 9

Fluoroquinolones are poorly active against enterococci. Recently, plasmid-borne resistance to fluoroquinolones due to the qnr gene was reported in members of the Enterobacteriaceae family. The gene encodes a pentapeptide repeat protein that protects DNA gyrase from inhibition by fluoroquinolones. We have identified in the genome of Enterococcus faecalis V583 a qnr-like gene, named E. faecalis qnr (qnr(E. faecalis)), encoding a putative pentapeptide repeat protein that shares 25% identity with Qn ...[more]

PMID: 17620379

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Project description:Enterococcus faecalis is a commensal of the human gastrointestinal tract; it is also an opportunistic pathogen and one of the leading causes of hospital-acquired infections. E. faecalis produces biofilms that are highly resistant to antibiotics, and it has been previously reported that certain genes of the epa operon contribute to biofilm-associated antibiotic resistance. Despite several studies examining the epa operon, many gene products of this operon remain annotated as hypothetical proteins. Here, we further explore the epa operon; we identified epaQ, currently annotated as encoding a hypothetical membrane protein, as being important for biofilm formation in the presence of the antibiotic daptomycin. Mutants with disruptions of epaQ were more susceptible to daptomycin relative to the wild type, suggesting its importance in biofilm-associated antibiotic resistance. Furthermore, the ΔepaQ mutant exhibited an altered biofilm architectural arrangement and formed small aggregates in liquid cultures. Our cumulative data show that epa mutations result in altered polysaccharide content, increased cell surface hydrophobicity, and decreased membrane potential. Surprisingly, several epa mutations significantly increased resistance to the antibiotic ceftriaxone, indicating that the way in which the epa operon impacts antibiotic resistance is antibiotic dependent. These results further define the key role of epa in antibiotic resistance in biofilms and in biofilm architecture.IMPORTANCE E. faecalis is a common cause of nosocomial infection, has a high level of antibiotic resistance, and forms robust biofilms. Biofilm formation is associated with increased antibiotic resistance. Therefore, a thorough understanding of biofilm-associated antibiotic resistance is important for combating resistance. Several genes from the epa operon have previously been implicated in biofilm-associated antibiotic resistance, pathogenesis, and competitive fitness in the GI tract, but most genes in this locus remain uncharacterized. Here, we examine epaQ, which has not been characterized functionally. We show that the ΔepaQ mutant exhibits reduced biofilm formation in the presence of daptomycin, altered biofilm architecture, and increased resistance to ceftriaxone, further expanding our understanding of the contribution of this operon to intrinsic enterococcal antibiotic resistance and biofilm growth.

Dataset Information

Role of a qnr-like gene in the intrinsic resistance of Enterococcus faecalis to fluoroquinolones.

Publications

Role of a qnr-like gene in the intrinsic resistance of Enterococcus faecalis to fluoroquinolones.

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