INDUCIBLE AND CONSTITUTIVE EXPRESSION OF RESISTANCE TO GLYCOPEPTIDES AND VANCOMYCIN DEPENDENCE IN GLYCOPEPTIDE-RESISTANT ENTEROCOCCUS-AVIUM

A clinical isolate of Enterococcus avium, Ea1, which exhibited inducib le, low-level resistance to vancomycin and teicoplanin, and two mutant s selected from this strain, Ea3 and Ea31, were studied, Ea3 was vanco mycin dependent and derived from Ea1, while Ea31 was not vancomycin de pendent, was constitutively resistant, and was derived from Ea3. Hybri dization studies revealed that vanA was present in Ea1 and suggested t hat it was located on a high-molecular-weight plasmid, Ln the absence of induction, Ea1 synthesized only the natural UDP-MurNAc-pentapeptide precursor, and after induction it synthesized an additional precursor identified as UDP-MurNAc-tetrapeptide-D-lactate. The latter was the o nly precursor found in Ea3 and Ea31, even after precursor accumulation . From these results, we infer that (i) the low level of resistance to glycopeptides in strain Ea1 may be in part due to the residual synthe sis of the normal precursor and (ii) the vancomycin dependence of muta nt Ea3 could be due to the fact that this strain does not produce any peptidoglycan precursor in the absence of induction.