Measures of Susceptibility from a Spiral Gradient of Drug Concentrations

  • Samuel Schalkowsky
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 349)


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.


Minimum Inhibitory Concentration Growth Transition Clinical Laboratory Standard Zone Diameter Twofold Dilution 
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  1. 1.
    S. Schalkowsky, Plating systems, in: “Foodborne Microorganisms and their Toxins: Developing Methodology,” Pierson M. D. and Stern N. J. ed., Marcel Dekker, New York (1986).Google Scholar
  2. 2.
    L. S. Weckbach and J. L. Staneck, Examination of spiral gradient endpoint (SGE) for the determination of MICs [abstract no. C-65]. In: Program and abstracts of the 27th annual meeting of American Society for Microbiology. Washington, DC: American Society for Microbiology, (1987).Google Scholar
  3. 3.
    J. H. Paton, H. A. Holt and M. J. Bywater, Measurement of MICs of antibacterial agents by spiral gradient endpoint compared with conventional dilution method. Int. J. Experimental and Clin. Chemother. 3:1, 31–38 (1990).Google Scholar
  4. 4.
    G. B. Hill and S. Schalkowsky, Development and evaluation of the spiral gradient endpoint method for susceptibility testing of anaerobic gram-negative bacilli Rev.Infect. Diseases 12 suppl. 2, S200–S209 (1990).CrossRefGoogle Scholar
  5. 5.
    H. M. Wexler, E. Molitoris, F. Jashnian and S. M. Finegold, Comparison of spiral gradient and conventional agar dilution for susceptibility testing of anaerobic bacteria, Antimicrob. Agents Chemother. 35:6, 1196–1202 (1991).CrossRefGoogle Scholar
  6. 6.
    National Committee for Clinical Laboratory Standards, Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically, 2nd ed. Approved standard M7–A2. National Committee for Clinical Laboratory Standards, Villanova, Pa. (1990).Google Scholar
  7. 7.
    National Committee for Clinical Laboratory Standards, Methods for antimicrobial susceptibility testing of anaerobic bacteria, 2nd ed. Approved standard M11–A2. National Committee for Clinical Laboratory Standards, Villanova, Pa. (1990).Google Scholar
  8. 8.
    S. Schalkowsky, SGE susceptibility measures. Appendix A in User Guide: Spiral Gradient Endpoint Antimicrobial Susceptibility Test. Spiral System Instruments Inc., Bethesda MD (August 1990).Google Scholar
  9. 9.
    P. Summanen, E. Molitoris, H. M. Wexler and S. M. Finegold, Use of triphenyltetrazolium chloride color reaction as an aid in susceptibility testing of Bilophila wadsworthia, Abstract 182, 31st Interscience Conference on Antimicrobial Agents and Chemotherapy (1991).Google Scholar
  10. 10.
    H. M. Ericsson and J. C. Sherris, Antibiotic sensitivity testing. Report of an international collaborative study. Acta Pathol. Microbiol. Scand. (B) Suppl. 217:67–68 (1971).Google Scholar
  11. 11.
    J. A. Korvick and V. L. Yu, Antimicrobial agent therapy for Pseudomonas aeruginosa. Antimicrob. Agents and Chemother. 35:11, 2167–2172 (1991).CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1994

Authors and Affiliations

  • Samuel Schalkowsky
    • 1
  1. 1.Spiral System Instruments, Inc.BethesdaUSA

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