Agar well diffusion assay testing of bacterial susceptibility to various antimicrobials in concentrations non-toxic for human cells in culture.

Previously, we showed that microbial susceptibility to antimicrobials in concentrations non-toxic for human cells in culture could be tested using the wet disc topical antimicrobial assay. In this report, wet disc assay and agar well diffusion assay results were compared testing the susceptibility of Ps. aeruginosa isolates from burn patients to concentrations of Polymyxin B non-toxic for cultured cells. Both assays were performed on the same agar plates. No differences in results were observed. Further agar well diffusion assay testing showed that susceptibility/resistance could be demonstrated when testing several antimicrobials in concentrations non-toxic for cultured cells against a variety of bacteria isolated from burn patients. Therefore, the more familiar agar well diffusion as well as the wet disc assay can be used to test microbial susceptibility to these concentrations of antimicrobials.