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

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: 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.

Difference in killing activity of caspofungin and paradoxical growth between Candida albicans and C. krusei clinical isolates in different media.

Minimum fungicidal concentration (mFC) of caspofungin was determined against 16 Candida albicans and 16 C. krusei in Rpmi-1640 and antibiotic medium 3 (Am3). time-kill tests were performed on six C. albicans and four C. krusei strains at 0.06-16 mg/l caspofungin. mFC ranges after 48 h were 0.5-1 and 1-2 mg/l for C. albicans and C. krusei, respectively; one C. albicans and the C. krusei reference strain showed paradoxical growth (pG) in Rpmi-1640, respectively. in killing experiments, after 48 h caspofugin was fungicidal against two and four C. albicans in Rpmi-1640 (at 16 mg/l) and in Am3 (at >0.5 mg/l), respectively; pG was noted in three and two cases, respectively. Caspofungin at >2 and 0.5 mg/l was fungicidal against all tested C. krusei strains even after 24 h in Rpmi-1640 and Am3, respectively. Killing activity of caspofungin against C. albicans and C. krusei could be exactly measured only by killing curves.

Correlation of posaconazole minimum fungicidal concentration and time kill test against nine Candida species.

OBJECTIVES: We evaluated the in vitro activity of posaconazole against nine Candida species using minimum fungicidal concentration (MFC) measurements and time-kill methods. METHODS: MFCs of posaconazole were determined for 209 clinical isolates (32 Candida albicans, 30 Candida glabrata, 21 Candida tropicalis, 29 Candida krusei, 28 Candida parapsilosis sensu stricto, 50 Candida inconspicua, 13 Candida kefyr, 3 Candida lusitaniae and 3 Candida guilliermondii) and 7 ATCC Candida strains. The following strains were tested in time-kill studies: 3 strains each of C. glabrata, C. kefyr, C. guilliermondii and C. lusitaniae; 2 C. tropicalis; 4 C. albicans; 4 C. inconspicua; 9 C. krusei; 12 C. parapsilosis; and 7 ATCC strains. RESULTS: Posaconazole was fungicidal in both MFC and time-kill experiments (at 2 mg/L within 48 h in time-kill assays) against each C. krusei, C. inconspicua and C. lusitaniae strain and was fungistatic against each C. albicans, C. glabrata, C. tropicalis and C. guilliermondii strain. For the C. parapsilosis strains, posaconazole MFCs were

Posaconazole susceptibility testing against Candida species: comparison of broth microdilution and E-test methods.

Posaconazole (POS) is a newer triazole with activity against yeasts and moulds. POS and fluconazole were tested in vitro against 32 Candida albicans, 30 C. glabrata, 21 C. tropicalis, 29 C. krusei, 28 C. parapsilosis, 50 C. inconspicua, 13 C. kefyr and 5 C. famata isolates using CLSI broth microdilution method (BMD). We compared E-test and a modified BMD using polyethylene-glycol (PEG) as solvent to the CLSI method. BMDs and E-test were performed according to CLSI and the manufacturer's instructions respectively. Geometric means of POS MICs using BMD were 0.71, 0.22 and 0.21 microg ml(-1) against C. glabrata, C. krusei and C. inconspicua, respectively, and remained below 0.1 microg ml(-1) against all other species tested. One of two C. albicans and two of three C. glabrata isolates resistant to fluconazole showed MICs above 8 microg ml(-1) to POS. The impact of using PEG instead of DMSO had only a minor effect (agreements above 95% with the exception of C. parapsilosis). E-tests read after 24 h showed good agreement with the BMD. POS exhibited excellent in vitro activity against Hungarian Candida strains. E-test showed good correlation with the CLSI method, but to facilitate the comparability of results we believe that DMSO should be used as solvent in the BMD.

In vitro study of Candida tropicalis isolates exhibiting paradoxical growth in the presence of high concentrations of caspofungin.

Paradoxical growth was noted in RPMI 1640 and antibiotic medium 3 in the case of 14 and 1 of 15 Candida tropicalis strains, respectively, at a caspofungin concentration of 12.5 microg/ml using minimum fungicidal concentration tests. Time-kill assays showed that against isolates killed at lower concentrations, caspofungin at a concentration of 12.5 microg/ml was only fungistatic.