Copyright © 1997, American Society for Microbiology The Effect of Vancomycin on the Structure of Vancomycin-Susceptible

Williamson et al. previously showed that a strain of Entero-coccus faecium with low-level resistance to vancomycin grown in the presence of one-half the MIC of vancomycin showed bizarre cell forms with abnormal septa without apparent cell division (3). In the current work, 10 strains of E. faecium suscep-tible to vancomycin (MIC,,2 mg/ml) and 10 resistant strains (MIC,.400 mg/ml) which were also resistant to teicoplanin (MIC,.40 mg/ml) were DNA fingerprinted to exclude the possibility of strain duplication. Vancomycin at one-half the MIC (0.3 to 0.6 mg/ml for susceptible and 200 to 250 mg/ml for resistant strains) was added to 10-ml volumes of Trypticase soy broth (TSB) which were inoculated with 100 ml of a 1/10 dilution of the respective 24-h TSB cultures. The products of incubation were sampled periodically throughout the 24-h pe-riod of incubation for Gram staining. Two strains resistant t