Skip to main content
NCBI home page
Antimicrobial Agents and Chemotherapy logoLink to Antimicrobial Agents and Chemotherapy
. 1976 Oct;10(4):721–726. doi: 10.1128/aac.10.4.721

Antimicrobial Susceptibility Testing of Yeasts: a Turbidimetric Technique Independent of Inoculum Size

John N Galgiani *, David A Stevens †
PMCID: PMC429820  PMID: 984806

Abstract

The current development of potent antifungal drugs necessitates reliable methods of in vitro susceptibility testing of clinical isolates. Other laboratories have noted with some antimicrobials that conventional tube dilution visual end points for determining minimal inhibitory concentrations (MIC) vary markedly with the inoculum. With seven isolates (four species) we compared the conventional method with one developed with a spectrophotometer. Yeasts were diluted to inocula of 102 to 105 cells/ml and incubated at 37°C with 5-fluorocytosine or miconazole or without drug in a synthetic defined medium. At frequent intervals MICs were determined by the lowest drug concentration without visible turbidity. Concurrently, the percent transmission of each tube was measured and an inhibitory concentration (IC½) was calculated from the turbidimetric measurements. MICs of both drugs for all strains varied with the inoculum. Intrastrain differences averaged 128-fold for miconazole and greater than 8-fold with 5-fluorocytosine. This variability in MIC occurred when readings were made after 12 to 48 h of incubation. In contrast, IC½ values of all isolates varied less than two-fold with the same range of inocula. Most isolates showed this independence when measured at 48 h. Fast-growing yeasts showed greater IC½ variability unless the turbidimetric measurements were taken earlier while the drug-free growth was still in a rapid growth phase. This method is reproducible, inoculum independent, rapid, free from subjectivity and observer variability, and suitable for adaptation to a clinical setting.

Full text

PDF
721

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Bennett J. E. Chemotherapy of systemic mycoses (first of two parts). N Engl J Med. 1974 Jan 3;290(1):30–32. doi: 10.1056/NEJM197401032900107. [DOI] [PubMed] [Google Scholar]
  2. Bindschadler D. D., Bennett J. E. A pharmacologic guide to the clinical use of amphotericin B. J Infect Dis. 1969 Oct;120(4):427–436. doi: 10.1093/infdis/120.4.427. [DOI] [PubMed] [Google Scholar]
  3. Block E. R., Jennings A. E., Bennett J. E. Variables influencing susceptibility testing of Cryptococcus neoformans to 5-fluorocytosine. Antimicrob Agents Chemother. 1973 Oct;4(4):392–395. doi: 10.1128/aac.4.4.392. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Frei E., 3rd, Levin R. H., Bodey G. P., Morse E. E., Freireich E. J. The nature and control of infections in patients with acute leukemia. Cancer Res. 1965 Oct;25(9):1511–1515. [PubMed] [Google Scholar]
  5. Hamilton J. D., Elliott D. M. Combined activity of amphotericin B and 5-fluorocytosine against Cryptococcus neoformans in vitro and in vivo in mice. J Infect Dis. 1975 Feb;131(2):129–137. doi: 10.1093/infdis/131.2.129. [DOI] [PubMed] [Google Scholar]
  6. Hoeprich P. D., Finn P. D. Obfuscation of the activity of antifungal antimicrobics by culture media. J Infect Dis. 1972 Oct;126(4):353–361. doi: 10.1093/infdis/126.4.353. [DOI] [PubMed] [Google Scholar]
  7. Seelig M. S., Speth C. P., Kozinn P. J., Taschdjian C. L., Toni E. F., Goldberg P. Patterns of Candida endocarditis following cardiac surgery: Importance of early diagnosis and therapy (an analysis of 91 cases). Prog Cardiovasc Dis. 1974 Sep-Oct;17(2):125–160. doi: 10.1016/0033-0620(74)90027-9. [DOI] [PubMed] [Google Scholar]

Articles from Antimicrobial Agents and Chemotherapy are provided here courtesy of American Society for Microbiology (ASM)

RESOURCES