Effects of incubation temperature, inoculum size, and medium on agreement of macro- and microdilution broth susceptibility test results for yeasts

R. A. Cook, K. A. McIntyre, John N Galgiani

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

We examined the effects of temperature and inoculum on the agreement of macro- and microdilution broth MICs of five antifungal agents against six isolates of Candida species or Torulopsis glabrata. Incubation temperature affected results with amphotericin B, flucytosine, fluconazole, and SCH 39304, producing better agreement at 35°C than at 37°C. Agreement between methods was better with an inoculum size of 102 than with one of 104 yeast cells per ml in testing fluconazole or SCH 39304, and the discrepancies seen with a higher incubation temperature and a larger inoculum appeared to be additive. However, inoculum size did not seem to affect agreement between methods in testing amphotericin B, flucytosine, or ketoconazole, Regardless of test conditions, macrodilution broth MICs of amphotericin B for different isolates were strikingly higher than microdilution test MICs, with mean differences being greater than ninefold under some test conditions. We conclude that for most currently available antifungal agents, an incubation temperature of 35°C and a starting yeast inoculum of less than 104 cells per ml improve the agreement between macro- and microdilution broth tests.

Original languageEnglish (US)
Pages (from-to)1542-1545
Number of pages4
JournalAntimicrobial Agents and Chemotherapy
Volume34
Issue number8
StatePublished - 1990
Externally publishedYes

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Amphotericin B
Yeasts
Candida glabrata
Flucytosine
Temperature
Fluconazole
Antifungal Agents
Ketoconazole

ASJC Scopus subject areas

  • Pharmacology (medical)

Cite this

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abstract = "We examined the effects of temperature and inoculum on the agreement of macro- and microdilution broth MICs of five antifungal agents against six isolates of Candida species or Torulopsis glabrata. Incubation temperature affected results with amphotericin B, flucytosine, fluconazole, and SCH 39304, producing better agreement at 35°C than at 37°C. Agreement between methods was better with an inoculum size of 102 than with one of 104 yeast cells per ml in testing fluconazole or SCH 39304, and the discrepancies seen with a higher incubation temperature and a larger inoculum appeared to be additive. However, inoculum size did not seem to affect agreement between methods in testing amphotericin B, flucytosine, or ketoconazole, Regardless of test conditions, macrodilution broth MICs of amphotericin B for different isolates were strikingly higher than microdilution test MICs, with mean differences being greater than ninefold under some test conditions. We conclude that for most currently available antifungal agents, an incubation temperature of 35°C and a starting yeast inoculum of less than 104 cells per ml improve the agreement between macro- and microdilution broth tests.",
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AU - Galgiani, John N

PY - 1990

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N2 - We examined the effects of temperature and inoculum on the agreement of macro- and microdilution broth MICs of five antifungal agents against six isolates of Candida species or Torulopsis glabrata. Incubation temperature affected results with amphotericin B, flucytosine, fluconazole, and SCH 39304, producing better agreement at 35°C than at 37°C. Agreement between methods was better with an inoculum size of 102 than with one of 104 yeast cells per ml in testing fluconazole or SCH 39304, and the discrepancies seen with a higher incubation temperature and a larger inoculum appeared to be additive. However, inoculum size did not seem to affect agreement between methods in testing amphotericin B, flucytosine, or ketoconazole, Regardless of test conditions, macrodilution broth MICs of amphotericin B for different isolates were strikingly higher than microdilution test MICs, with mean differences being greater than ninefold under some test conditions. We conclude that for most currently available antifungal agents, an incubation temperature of 35°C and a starting yeast inoculum of less than 104 cells per ml improve the agreement between macro- and microdilution broth tests.

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