Resistance (R) of ASP to itraconazole (ITR) and other azoles is a growing concern that merits monitoring by standardized susceptibility testing. We used CLSI BMD and the European Committee for Antimicrobial Susceptibility Testing (EUCAST) method to test ASP, including amphotericin B (AMB)- and azole-R strains.
CLSI and EUCAST methods were used to test 78 ASP (20 A. flavus [AFL], 22 A. fumigatus [AFM], 13 A. niger [ANG] and 23 A. terreus [ATR]), including15 AMB-R (MIC, ≥ 2 Âµg/ml) ATR strains and 10 ITR-R (MIC, ≥ 4 Âµg/ml) AFM (7), ANG (2) and ATR (1). Comparators included caspofungin (CSF), ITR, and posaconazole (PSC). All isolates were read visually after 48-h incubation. For ANF and CSF the minimum effective concentration (MEC) was determined as described by CLSI (M38-A2). For ITR, PSC, and VRC an MIC endpoint of complete growth inhibition was used for both methods.
CLSI and EUCAST methods were highly concordant for ANF, VRC and all comparators. The essential agreement (EA; Â± 2 log2 dilutions) was 100% for all comparisons with the exception of PSC and ATR (EA = 91.3%). Both ANF and VRC were highly active against all isolates. The MEC/MIC90 values (Âµg/ml) for ANF, CSF, ITR, PSC, and VRC, respectively, were as follows for each species: AFL (8804;0.008, 0.12, 1, 1, 1), AFM (0.015, 0.12, >8, 1, 4), ANG (0.03, 0.12, 4, 1, 2), ATR (0.015, 0.12, 1, 0.5, 1). ANF was very active against AMB-R strains of ATR (MEC range, 0.008-0.015 Âµg/ml) and ITR-R strains of AFM (MEC range, 0.008-0.015 Âµg/ml), ANG (MEC, 0.008 Âµg/ml) and ATR (MEC, 0.008 Âµg/ml). VRC was active against AMB-R strains of ATR (MIC range of 0.25- >8 Âµg/ml) but showed cross-resistance with ITR against ITR-R strains of AFM (MIC range, of 0.25-8 Âµg/ml).
ANF showed excellent activity against AMB- and ITR-R strains of ASP. VRC was active against AMB-R ATR, but demonstrated cross-resistance with ITR for ITR-R AFM. In vitro susceptibility testing of ANF, VRC and other mould-active antifungal agents may be accomplished by either CLSI or EUCAST BMD methods with comparable results.
Full conference title:
- ASM 111th (2011)