Vancomycin binding to cell walls of non-streptococcal vancomycin-resistant bacteria.

The availability of peptidoglycan for binding to vancomycin was investigated in intrinsically vancomycin-resistant clinical isolates of Leuconostoc mesenteroides, Lactobacillus viridescens and Pediococcus pentosaceus. Intrinsic vancomycin resistance expressed by L. mesenteroides and P. pentosaceus was the result of poor binding of vancomycin to native or SDS-treated cell walls. Pre-exposure of L. viridescens to vancomycin decreased the subsequent binding of vancomycin to the cell walls, suggesting an alternative mechanism to that found in high-level vancomycin-resistant enterococci and intrinsically-resistant L. mesenteroides and P. pentosaceus. Vancomycin binding was sensitive to substitution of larger side chains at the C-terminus. Variations of peptidoglycan peptide types found in L. mesenteroides, L. viridescens and P. pentosaceus could account for their intrinsic vancomycin resistance.