Genetic basis for vancomycin-enhanced cephalosporin susceptibility in vancomycin-resistant enterococci revealed using counterselection with dominant-negative thymidylate synthase.
Antimicrob Agents Chemother
; 58(3): 1556-64, 2014.
Article
em En
| MEDLINE
| ID: mdl-24366749
ABSTRACT
Antibiotic-resistant enterococci are major causes of hospital-acquired infections. All enterococci are intrinsically resistant to most cephalosporins, antibiotics in the beta-lactam family that impair peptidoglycan synthesis by inactivating the transpeptidases responsible for cross-linking. In addition, clinical isolates of enterococci often possess acquired resistance to vancomycin, a glycopeptide antibiotic that impairs peptidoglycan biosynthesis by a mechanism distinct from that of the beta-lactams, namely, by binding to the D-Ala-D-Ala termini found in peptidoglycan precursors to prevent their utilization by biosynthetic transglycosylases. Antimicrobial synergism between vancomycin and beta-lactams against vancomycin-resistant enterococci was originally described decades ago, but the genetic basis for synergy has remained unknown. Because a complete understanding of the mechanism underlying synergy between vancomycin and beta-lactams might suggest new targets or strategies for therapeutic intervention against antibiotic-resistant enterococci, we explored the genetic basis for synergy between vancomycin and cephalosporins in Enterococcus faecalis. To do so, we developed a counterselection strategy based on a dominant-negative mutant of thymidylate synthase and implemented this approach to create a panel of mutants in vancomycin-resistant E. faecalis. Our results confirm that vancomycin promotes synergy by inducing expression of the van resistance genes, as a mutant in which the van genes are expressed in the absence of vancomycin exhibits susceptibility to cephalosporins. Further, we show that peptidoglycan precursors substituted with D-Ala-D-Lac are not required for vancomycin-enhanced cephalosporin sensitivity. Instead, production of the D,D-carboxypeptidase VanYB is both necessary and sufficient to dramatically sensitize E. faecalis to cephalosporins.
Texto completo:
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Base de dados:
MEDLINE
Assunto principal:
Timidilato Sintase
/
Cefalosporinas
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Enterococcus faecalis
/
Resistência a Vancomicina
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Antibacterianos
Idioma:
En
Ano de publicação:
2014
Tipo de documento:
Article
País de afiliação:
Estados Unidos