Time-kill studies investigating the killing activity of caspofungin against Candida dubliniensis: Comparing RPMI-1640 and antibiotic medium 3

I. Varga, G. Sóczó, G. Kardos, L. Majoros

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Abstract

Objectives: We evaluated the in vitro activity of caspofungin against Candida dubliniensis strains using MIC and minimum fungicidal concentration (MFC) measurements and time-kill methodology. Methods: Weused six C. dubliniensis clinical isolates and the CD 36 type strain. MICs and MFCs of caspofungin were determined using the standard broth microdilution method with normal (103 cells/mL) and elevated (105 cells/mL) starting inocula in RPMI-1640 and antibiotic medium 3 (AM3). MIC was determined after 24 h, and plating for MFC determination was performed after 48 h. In time-kill tests, all strains were tested at 0.06-16 mg/L caspofungin concentrations in RPMI-1640 and AM3. Results: In RPMI-1640, the MIC range was 0.06-8 mg/L. Trailing growth was observed regardless of the starting inoculum after 48 h, but not after 24 h. In AM3 regardless of starting inoculum, MICs were 0.03 mg/L. After 48 h, trailing was not detected; two isolates grew at a concentration of 8 mg/L using 105 cells/mL as the starting inoculum [paradoxical growth (PG)]. All MFCs in RPMI-1640 and AM3 were >8 and ≤0.12 mg/L, respectively. In AM3, all but a single isolate showed PG in the MFC tests. Time-kill tests confirmed the results obtained by MFC tests both in RPMI-1640 and AM3. Conclusions: In vitro activity of caspofungin against C. dubliniensis depended on the starting inoculum and medium used. Using AM3 eliminated trailing from MIC determinations but not PG in MIC, MFC and time-kill tests.

Original languageEnglish
Pages (from-to)149-152
Number of pages4
JournalJournal of Antimicrobial Chemotherapy
Volume62
Issue number1
DOIs
Publication statusPublished - Jul 1 2008

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Keywords

  • Eagle effect
  • Fungicidal
  • Paradoxical growth

ASJC Scopus subject areas

  • Pharmacology
  • Microbiology (medical)
  • Infectious Diseases
  • Pharmacology (medical)

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