Inducible and constitutive expression of vanC-1-encoded resistance to vancomycin in Enterococcus gallinarum.
Clinical isolates Enterococcus gallinarum AIB39 and E. gallinarum GS1 were studied to establish whether the expression of vanC-1-mediated resistance may be inducible or constitutive. By growth curve analysis, strain AIB39 exhibited the same lag period (i.e., 1 to 1.5 h) whether it was subcultured to unsupplemented brain heart infusion broth or broth containing 6 micrograms of vancomycin per ml, a growth pattern typical of constitutively expressed resistance. Use of high-performance liquid chromatography (HPLC) to separate peptidoglycan precursor extracts substantiated this finding because the serine-terminating pentapeptide precursor UDP-MurNAc-L-Ala-D-Glu-L-Lys-D-Ala-D-Ser was produced in the presence and absence of vancomycin, whereas no UDP-MurNAc-L-Ala-D-Glu-L-Lys-D-Ala-D-Ala was detected. In contrast, results with strain GS1 were consistent with inducible expression. GS1 demonstrated a lag time that was 3 to 4 h longer when it was subcultured to vancomycin-containing broth than when it was subcultured in unsupplemented broth. HPLC analysis showed that in the absence of vancomycin only UDP-MurNAc-L-Ala-D-Glu-L-Lys-D-Ala-D-Ala was detected, but in the presence of drug only UDP-MurNAc-L-Ala-D-Glu-L-Lys-D-Ala-D-Ala was found. Inducible expression of vanC-1-mediated resistance in E. gallinarum is consistent with recent findings suggesting the presence of at least two ligases in this species. Although vanC-1 may be intrinsic to E. gallinarum, our findings raise doubt regarding the natural mechanism of this gene's expression.
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000502:physiology; D001483:Base Sequence; D004352:Drug Resistance, Microbial / Q000235:genetics; D016983:Enterococcus / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D004790:Enzyme Induction; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D014640:Vancomycin / Q000494:pharmacology*
D001426:Bacterial Proteins; C079914:VanC protein, Bacteria; D014640:Vancomycin