Specificity of Induction of the vanA and vanB Operons in Vancomycin-Resistant Enterococci by Telavancin

Telavancin is a bactericidal, semisynthetic lipoglycopeptide indicated in the United States for the treatment of complicated skin and skin structure infections caused by susceptible Gram-positive bacteria and is under investigation as a once-daily treatment for nosocomial pneumonia. The related vanA and vanB gene clusters mediate acquired resistance to glycopeptides in enterococci by remodeling the dipeptide termini of peptidoglycan precursors from D-alanyl-D-alanine (D-Ala-D-Ala) to D-alanyl-D-lactate (D-Ala-D-Lac). In this study, we assessed the ability of telavancin to induce the expression of van genes in VanA-and VanB-type strains of vancomycin-resistant enterococci. Vancomycin, teicoplanin, and telavancin efficiently induced VanX activity in VanA-type strains, while VanX activity in VanB-type isolates was inducible by vancomycin but not by teicoplanin or telavancin. In VanA-type strains treated with vancomycin or telavancin, high levels of D-Ala-D-Lac-containing pentadepsipeptide were measured, while D-Ala-D-Ala pentapeptide was present at very low levels or not detected at all. In VanB-type strains, vancomycin but not telavancin induced high levels of pentadepsipeptide, while pentapeptide was not detected. Although vancomycin, teicoplanin, and telavancin induced similar levels of VanX activity in VanA-type strains, these organisms were more sensitive to telavancin, which displayed MIC values that were 32- and 128-fold lower than those of vancomycin and teicoplanin, respectively.