Activity of glycopeptides against vancomycin-resistant gram-positive bacteria

Gram-positive bacteria resistant to vancomycin are rare; but they include members of the genera Leuconostoc, Lactobacillus, and Pediococcus, as well as recently emerging vancomycin-resistant strains of Enterococcus faecium and Enterococcus faecalis. Vancomycin, teicoplanin, and several vancomycin derivatives were tested for their activities against vancomycin-resistant gram-positive bacteria. Vancomycin-resistant E. faecium and E. faecalis were generally cross-resistant to other glycopeptides, but some N-substituted vancomycin derivatives were active against the resistant strains, with MICs of 2 to 32 micrograms/ml. These vancomycin derivatives also had significant levels of activity against intrinsically vancomycin-resistant organisms such as Leuconostoc sp. While vancomycin resistance in E. faecium and E. faecalis was inducible, resistance in members of the genera Leuconostoc, Lactobacillus, and Pediococcus appeared to be expressed constitutively. Antibody to a vancomycin-induced membrane protein found in membranes of resistant enterococci did not detect a cross-reacting protein in other vancomycin-resistant species.