Skip to main content

Spiral gradient endpoint method compared to standard agar dilution for susceptibility testing of anaerobic gram-negative bacilli.

Publication ,  Journal Article
Hill, GB
Published in: J Clin Microbiol
May 1991

More efficient and reproducible alternative methods of performing agar dilution susceptibility testing are desirable, particularly for anaerobic bacteria. Anaerobes generally grow more reliably on solid media than they do in broth microdilution wells. A new method, the revised spiral gradient endpoint (SGE) method, was evaluated against the standard agar dilution (SAD) method by using a wide variety of anaerobic gram-negative bacilli (161 strains) and eight antimicrobial agents. For the SGE method, a spiral plater was used to set up a concentration gradient of an antimicrobial agent within an agar plate across which bacterial strains were inoculated as radial streaks. After incubation, the MIC of the antimicrobial agent was calculated from the radial endpoint location where bacterial growth ceased along the streak. The MICs for 90% of strains tested (in micrograms per milliliter) and the cumulative percentages of susceptible strains at the breakpoints for the SGE and SAD methods, respectively, and for all 161 strains were as follows: for metronidazole, 2 and 100 versus 2 and 100; for imipenem, 1 and 99 versus 0.5 and 98; for ampicillin-sulbactam, 8 and 97 versus 8 and 98; for clindamycin, 4 and 90 versus 4 and 91; for cefoxitin, 32 and 95 versus 32 and 95; for mezlocillin, 256 and 88 versus greater than 128 and 86; for ampicillin, greater than or equal to 256 and 51 versus greater than 64 and 51; and for penicillin (in units per milliliter), greater than or equal to 512 and 71 versus greater than 64 and 65. The excellent agreement of these data and the greater sensitivity reproducibility, and efficiency of the revised SGE method warrant further evaluations. Assuming that these advantages are confirmed, the revised SGE method should be a useful alternative test method when detailed susceptibility data are desired.

Duke Scholars

Published In

J Clin Microbiol

DOI

ISSN

0095-1137

Publication Date

May 1991

Volume

29

Issue

5

Start / End Page

975 / 979

Location

United States

Related Subject Headings

  • Sensitivity and Specificity
  • Reproducibility of Results
  • Microbiology
  • Microbial Sensitivity Tests
  • Humans
  • Gram-Negative Anaerobic Bacteria
  • Evaluation Studies as Topic
  • Drug Resistance, Microbial
  • Agar
  • 3207 Medical microbiology
 

Citation

APA
Chicago
ICMJE
MLA
NLM
Hill, G. B. (1991). Spiral gradient endpoint method compared to standard agar dilution for susceptibility testing of anaerobic gram-negative bacilli. J Clin Microbiol, 29(5), 975–979. https://doi.org/10.1128/jcm.29.5.975-979.1991
Hill, G. B. “Spiral gradient endpoint method compared to standard agar dilution for susceptibility testing of anaerobic gram-negative bacilli.J Clin Microbiol 29, no. 5 (May 1991): 975–79. https://doi.org/10.1128/jcm.29.5.975-979.1991.
Hill, G. B. “Spiral gradient endpoint method compared to standard agar dilution for susceptibility testing of anaerobic gram-negative bacilli.J Clin Microbiol, vol. 29, no. 5, May 1991, pp. 975–79. Pubmed, doi:10.1128/jcm.29.5.975-979.1991.

Published In

J Clin Microbiol

DOI

ISSN

0095-1137

Publication Date

May 1991

Volume

29

Issue

5

Start / End Page

975 / 979

Location

United States

Related Subject Headings

  • Sensitivity and Specificity
  • Reproducibility of Results
  • Microbiology
  • Microbial Sensitivity Tests
  • Humans
  • Gram-Negative Anaerobic Bacteria
  • Evaluation Studies as Topic
  • Drug Resistance, Microbial
  • Agar
  • 3207 Medical microbiology