Commercially prepared strips are available from bioMérieux (Etest(r)) and Liofilchem
Diagnostici (MIC Test Strip(r)). The method consists of a predefined gradient of
antifungal drug concentrations on a plastic strip that is used to determine the MIC.
When the strip is applied on an inoculated agar surface, the antifungal agent is
immediately transferred to the agar matrix and after an incubation time, an
inhibition ellipse centered along the strip is formed. The recommended agar is RPMI
1640 supplemented with 2% glucose, prepared with MOPS in a 1.5% agar base. The
Etest(r) provides strips with fluconazole, itraconazole, amphotericin B, flucytosine,
voriconazole, posaconazole, and caspofungin. The MIC Test Strips(r) contains the same
antifungal drugs plus anidulafungin, micafungin and ketoconazole. The incubation time
range from 24-48 h for Candida species, from 48-72 h for C.
neoformans, and for filamentous fungi it lasts 16 h or longer depending
on the fungus' genus. The MIC is read directly from the scale at the point where the
edge of the ellipse intersects the strip. However, it is important to consider that,
as for any test evaluating the antimicrobial susceptibility, the medium formulation
and, in this case, the depth of the agar can strongly influence MIC results.
Therefore, the manufacturer's recommendations should be strictly followed to obtain
MICs using strips16
,17
,21 .
Results obtained by the E-test method shows a > 71% correlation with those
obtained by the AFST-EUCAST method. In both methods, the CLSI and EUCAST AFST, the
agar-based E-test has been proposed as a more sensitive technology to discriminate
strains of Candida species with fks mutations from
wild-type (WT) strains by virtue of much higher MIC results observed in mutant
strain. Considering Cryptococcus, the overall agreement level using
the E-test MICs and the EUCAST AFST-MICs seems to be higher for voriconazole,
fluconazole, itraconazole and flucytosine, than for amphotericin B, which has the
lowest level of agreement. Regarding filamentous fungi, the agreement is higher for
itraconazole than for amphotericin B, and the E-test method showed a good correlation
with the CLSI M38-AFST one to detect Aspergillus resistance.
Systematic comparisons between MIC results from reference laboratories and routine
results obtained using commercially available methods could be more representative
than the current practice to perform quality control with a specific set of reagents
using a limited number of isolates14 (link).
Diagnostici (MIC Test Strip(r)). The method consists of a predefined gradient of
antifungal drug concentrations on a plastic strip that is used to determine the MIC.
When the strip is applied on an inoculated agar surface, the antifungal agent is
immediately transferred to the agar matrix and after an incubation time, an
inhibition ellipse centered along the strip is formed. The recommended agar is RPMI
1640 supplemented with 2% glucose, prepared with MOPS in a 1.5% agar base. The
Etest(r) provides strips with fluconazole, itraconazole, amphotericin B, flucytosine,
voriconazole, posaconazole, and caspofungin. The MIC Test Strips(r) contains the same
antifungal drugs plus anidulafungin, micafungin and ketoconazole. The incubation time
range from 24-48 h for Candida species, from 48-72 h for C.
neoformans, and for filamentous fungi it lasts 16 h or longer depending
on the fungus' genus. The MIC is read directly from the scale at the point where the
edge of the ellipse intersects the strip. However, it is important to consider that,
as for any test evaluating the antimicrobial susceptibility, the medium formulation
and, in this case, the depth of the agar can strongly influence MIC results.
Therefore, the manufacturer's recommendations should be strictly followed to obtain
MICs using strips16
,17
,21 .
Results obtained by the E-test method shows a > 71% correlation with those
obtained by the AFST-EUCAST method. In both methods, the CLSI and EUCAST AFST, the
agar-based E-test has been proposed as a more sensitive technology to discriminate
strains of Candida species with fks mutations from
wild-type (WT) strains by virtue of much higher MIC results observed in mutant
strain. Considering Cryptococcus, the overall agreement level using
the E-test MICs and the EUCAST AFST-MICs seems to be higher for voriconazole,
fluconazole, itraconazole and flucytosine, than for amphotericin B, which has the
lowest level of agreement. Regarding filamentous fungi, the agreement is higher for
itraconazole than for amphotericin B, and the E-test method showed a good correlation
with the CLSI M38-AFST one to detect Aspergillus resistance.
Systematic comparisons between MIC results from reference laboratories and routine
results obtained using commercially available methods could be more representative
than the current practice to perform quality control with a specific set of reagents
using a limited number of isolates14 (link).
