Spiral Gradient Endpoint Test

Spiral Biotech, Inc.Gradient Endpoint (SGE) test provides highly sensitive and repeatable MIC determinations by the agar dilution method. One spiral gradient plate is equivalent to eight twofold dilution plates. A gradient of antimicrobial concentrations is produced in the agar by deposition of a stock solution with a spiral plater. Up to 15 test strains are then swabbed along radial lines on the surface of the agar.

The MIC is computed from the measured radial location of the transition from growth to no growth. Biocidal effects, which exhibit a sharp transition, can be distinguished from biostatic action, which results in progressively decreasing colony size in the tail.

The software computes MIC values and includes a correction for antimicrobial agent diffusion in the agar. Laboratory evaluations show equivalence of SGE MIC's with MIC's obtained by the standard agar dilution method, with superior repeatability and greater sensitivity since the endpoint is read from a continuous gradient.

The software includes analysis programs for quality control purposes and for evaluating the correlation between MIC's obtained by the SGE and other methods. Tables of cumulative-percent-susceptible and SGE rank-ordered data can be printed out. The data can also be exported for alternate analyses and displays.

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