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Antimicrobial Agents and Chemotherapy, Jul 1995, 1480-1484, Vol 39, No. 7
DF Sahm, L Free and S Handwerger
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.
Copyright © 1995 by the American Society for Microbiology. All rights reserved.
Inducible and constitutive expression of vanC-1-encoded resistance to vancomycin in Enterococcus gallinarum
Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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