Measures of Susceptibility from a Spiral Gradient of Drug Concentrations
The Spiral Gradient Endpoint (SGE) test utilizes the spiral plating method to deposit a liquid suspension in a spiral pattern on the surface of a pre-poured agar plate. Deposition is in exponentially decreasing amounts as the dispensing stylus moves radially outward, starting from the near-center of the plate. The original, and well established application of this method is for the enumeration of bacteria in the suspension, providing for substantial reduction in time and materials because the variable dilution on one spiral plate serves the same purpose as a multiple number of serially diluted pour-plates; colony counting is done only on the portion of the spiral plate containing well separated colonies1. Since its introduction in the mid 1970’s, this method has achieved wide-spread use for bacterial enumeration, demonstrating the ability of the instrumentation to maintain accuracy and reproducibility while greatly increasing test efficiency.
KeywordsMinimum Inhibitory Concentration Growth Transition Clinical Laboratory Standard Zone Diameter Twofold Dilution
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