INDUCIBLE AND CONSTITUTIVE EXPRESSION OF VANC-1-ENCODED RESISTANCE TOVANCOMYCIN IN ENTEROCOCCUS-GALLINARUM

Clinical isolates Enterococcus gallinarum AIB39 and E. gallinarum GS1 were studied to establish whether the expression of vanC-1-mediated re sistance may be inducible or constitutive. By growth curve analysis, s train AIB39 exhibited the same lag period (i.e., 1 to 1.5 h) whether i t was subcultured to unsupplemented brain heart infusion broth or brot h containing 6 mu g of vancomycin per mi, a growth pattern typical of constitutively expressed resistance, Use of high-performance liquid ch romatography (HPLC) to separate peptidoglycan precursor extracts subst antiated this finding because the serine-terminating pentapeptide prec ursor UDP-MurNAc-L-Ala-D-Glu-L-Lys-D-Ala-D-Ser was produced in the pre sence and absence of vancomycin, whereas no UDP-MurNAc-L-Ala-D-Glu-L-L ys-D-Ala-D-Ala was detected. In contrast, results with strain GSI were consistent with inducible expression, GS1 demonstrated a lag time tha t was 3 to 4 h longer when it was subcultured to vancomycin containing broth than when it was subcultured in unsupplemented broth. HPLC anal ysis 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 U DP-MurNAc-L-Ala-D-Glu-L-Lys-D-Ala-D-Ser was found, Inducible expressio n of vanC-1-mediated resistance in E. gallinarum is consistent with re cent findings suggesting the presence of at least two ligases in this species, Although vanC-1 may be intrinsic to E. gallinarum, our findin gs raise doubt regarding the natural mechanism of this gene's expressi on.