Time-kill studies investigating the killing activity of caspofungin against Candida dubliniensis: comparing RPMI-1640 and antibiotic medium 3.
OBJECTIVE
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
We used 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 (10(3) cells/mL) and elevated (10(5) 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 10(5) cells/mL as the starting inoculum [paradoxical growth (PG)]. All MFCs in RPMI-1640 and AM3 were >8 and < or =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.
Varga
I
I
Faculty of Dentistry, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary.
Sóczó
G
G
Kardos
G
G
Majoros
L
L
D000935:Antifungal Agents / Q000494:pharmacology*; D002175:Candida / Q000187:drug effects* / Q000302:isolation & purification; D002177:Candidiasis / Q000382:microbiology; D000077336:Caspofungin; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry; D054714:Echinocandins / Q000494:pharmacology*; D055666:Lipopeptides; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability; D013997:Time Factors
D000935:Antifungal Agents; D003470:Culture Media; D054714:Echinocandins; D055666:Lipopeptides; D000077336:Caspofungin