Evaluation of methods for detecting susceptibility of Staphylococcus aureus to Vancomycin

Objective To investigate the effective methods for detecting the susceptibility of Staphylococcus aureus to Vancomycin. Methods An isolate of h-VRSA (heterogeneous Vancomycin-resistant Staphylococcus aureus) isolated from clinical specimen was inoculated on the increasing concentration of vancomycin agars. Varied degree of vancomycin of resistant S. aureus were obtained. The susceptibilities of these S. aureus to vancomycin were tested by agar screening test, broth microdilution method, E-test, disk diffusion method and automated methods. Results Agar screening test, broth microdilution method and E-test are effective for detection of vancomycin-intermediate S. aureus VISA, but disk diffusion and automated methods could not detect VISA. Conclusion Broth microdilution method and E-test are acceptable methods for susceptibility testing of S. aureus to vancomycin. The laboratories using automated methods and disk diffusion method as routine susceptibility test should consider adding a vancomycin agar screen plate to enhance detection of VRSA and VISA.