Photoinactivation of vancomycin-resistant Enterococci and Bacillus subtilis by a novel norvancomycin–rhodamine B conjugate

Abstract

In order to accumulate photosensitizers on the cell walls of vancomycin-sensitive and vancomycin-resistant bacterial strains for labeling or/and photoinactivation of bacteria upon light irradiation, a simple and novel norvancomycin–rhodamine B (Van–Rh) conjugate was synthesized, characterized and confirmed using MALDI-TOF mass spectrometry. The properties of Van–Rh in photodynamic inactivation and fluorescent imaging of vancomycin-sensitive and vancomycin-resistant Enterococci (VRE) strains were investigated. The photodynamic assay indicated that Van–Rh effectively inactivated Bacillus subtilis (ATCC 6633), clinical isolates of VRE and Enterococcus faecalis (ATCC 51299, Van B genotype) with inactivation rates of 71, 54 and 47% at 9 μM upon 3 min of light exposure, respectively. Van–Rh enabled the fluorescent imaging of B. subtilis at 5 μM and two VRE strains at 20 μM, but not E. coli. The phototoxicity and binding affinity of rhodamine B were enhanced by conjugation with norvancomycin as an affinity ligand.