Bioelectrophoresis: a rapid procedure for the identification of antimicrobial agents.

Sensitivity discs were placed on 1% Noble agar for electrophoresis in a 20 mM phosphate-buffered, pH 8.5-8.8 system. The discs were removed after electrophoresis, and the agar was overlaid with Bacillus subtilis spores in Mueller-Hinton agar. After incubation at 37 C, each individual antimicrobial agent produced a distinctive identifying pattern of B. subtilis growth inhibition. The few antimicrobial agents with similar patterns could be easily differentiated by the use of a strain of Escherichia coli containing a multiple-resistance factor. Filter discs impregnated with commercial antibiotic preparations in buffer or serum yielded growth-inhibition patterns which usually resembled those obtained from corresponding sensitivity discs.