In vitro susceptibility of Candida species to micafungin: a comparison of methods
Abstract number: P2167
Gray V.L., Duddy N.E., Harris S., Howard S.J., Denning D.W., Moore C.B.
Objective: Clinical isolates of Candida species (n = 123) were taken from sterile and non-sterile sites to determine in vitro MIC's and minimum fungicidal concentrations (MFC) to the echinocandins micafungin and caspofungin. Differing methodologies for testing micafungin were employed for comparison.
Table 1. GM MIC's and MFC's for mica fungin are shown for various Candida species determined using various methods
Methods: Four methods were employed to determine MIC and MFC values to micafungin: EUCAST, Odds (Odds et. al., 2004, JCM 42:3475), CLSI M27-A2 (24 h and 48 h incubation). Parameters for EUCAST, Odds and CLSI methods respectively were as follows: inocula: 1×105, 1×103 and 1×103 CFU/ml; media: 2% glucose, no additional glucose and 2% glucose; incubation period: 24, 24 and 48 h; endpoint calculation: 50, 50 and 80%. Caspofungin was tested using the Odds method and 24 h MFC's. Data analysis was performed substituting 16 for >8 mg/L. Drug dilution stability at -80°C was assessed monthly using the EUCAST QC panel. For each species and method GM MIC and MFC values and ranges (mg/L) were calculated. MFC's (99% kill on 0.1 ml) for the CLSI method MFC's were recorded for both time points.
Results: Micafungin drug dilutions were stable for 6 months at -80°C. All species exhibited low MIC values to micafungin however inter-species variation was observed. Where the GM MIC was relatively higher, e.g. C. guilliermondii and C. parapsilosis, the differing methods produced notable intra-species variation in MIC values. Reproducibility data (20%) was excellent. For C. parapsilosis MIC's to micafungin varied from 0.1251.0, and caspofungin from 0.52 (Odds). MFC's for micafungin produced markedly different results dependent on the method utilised; the MFC value frequently ranged from <0.015 to >8 mg/L for a single isolate. A significant range of results for MFC's was noted for all species.
Conclusion: The differing methods did not produce markedly different MIC values for the echinocandin micafungin, with most isolates exhibiting low MIC's to the drug, typically lower than caspofungin. In contrast Micafungin and caspofungin MFC values varied significantly dependent on the method employed; this correlated with the inoculum level.
|Session name:||18th European Congress of Clinical Microbiology and Infectious Diseases|
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