Interlaboratory Comparison of Results of Susceptibility Testing with Caspofungin against Candida and Aspergillus Species

Abstract

Seventeen laboratories participated in a study of interlaboratory reproducibility with caspofungin microdilution susceptibility testing against panels comprising 30 isolates of Candida spp. and 20 isolates of Aspergillus spp. The laboratories used materials supplied from a single source to determine the influence of growth medium (RPMI 1640 with or without glucose additions and antibiotic medium 3 [AM3]), the same incubation times (24 h and 48 h), and the same end point definition (partial or complete inhibition of growth) for the MIC of caspofungin. All tests were run in duplicate, and end points were determined both spectrophotometrically and visually. The results from almost all of the laboratories for quality control and reference Candida and Aspergillus isolates tested with fluconazole and itraconazole matched the NCCLS published values. However, considerable interlaboratory variability was seen in the results of the caspofungin tests. For Candida spp. the most consistent MIC data were generated with visual "prominent growth reduction" (MIC 2 ) end points measured at 24 h in RPMI 1640, where 73.3% of results for the 30 isolates tested fell within a mode ؎ one dilution range across all 17 laboratories. MIC 2 at 24 h in RPMI 1640 or AM3 also gave the best interlaboratory separation of Candida isolates of known high and low susceptibility to caspofungin. Reproducibility of MIC data was problematic for caspofungin tests with Aspergillus spp. under all conditions, but the minimal effective concentration end point, defined as the lowest caspofungin concentration yielding conspicuously aberrant hyphal growth, gave excellent reproducibility for data from 14 of the 17 participating laboratories.

Paracoccidioides brasiliensis: chemical and molecular tools for research on cell walls, antifungals, diagnosis, taxonomy

“…On the other hand, values for Candida, a socalled caspofungin-sensitive genus, also shows ranges of action, e.g., C. albicans (0.03->16 lg/ml), C. krusei (0.03-2 lg/ml), C. glabrata (0.03-2 lg/ ml), C. tropicalis (0.06-1 lg/ml), or C. parapsilosis (0.5-16 lg/ml) [66]. As deduced by a large-scale study carried out simultaneously in 17 American and European laboratories, under strictly controlled identical conditions [67], considerable interlaboratory variability of MIC data on caspofungin are found when testing Candida and Aspergillus isolates, results that suggest the need for careful interpretation of the antifungal effect of this drug.…”

Use of Fluorescent Probes To Determine MICs of Amphotericin B and Caspofungin against Candida spp. and Aspergillus spp

“…The MIC of caspofungin for Candida spp. was defined as the lowest concentration of drug that significantly inhibits the organism compared to the drug-free growth control (15).…”

Global Surveillance of In Vitro Activity of Micafungin against Candida : a Comparison with Caspofungin by CLSI-Recommended Methods

“…BMD testing using RPMI 1640 broth, incubation for no longer than 24 h, and a MIC endpoint criterion of prominent reduction in growth (MIC-2 or Ն50% inhibition) relative to control growth provides both excellent reproducibility of results within and between laboratories and differentiation of isolates with "normal" or "wild-type" susceptibilities from glucan synthesis mutant strains with decreased susceptibilities to echinocandins (9,14).…”

“…In the present study we have employed the optimal testing conditions described previously (6,9,14), to examine geographic trends in the activity of micafungin against an interna- 3 of Candida pelliculosa, and 1 each of Candida rugosa and Candida zeylanoides. All isolates were obtained from blood or other normally sterile sites and represented individual infectious episodes.…”

“…Through a consensus process the Clinical and Laboratory Standards Institute (CLSI, formerly the National Committee for Clinical Laboratory Standards [NCCLS]) has developed a standardized method for broth microdilution (BMD) testing of echinocandins (i.e., caspofungin, micafungin, and anidulafungin) against Candida species (9,14). BMD testing using RPMI 1640 broth, incubation for no longer than 24 h, and a MIC endpoint criterion of prominent reduction in growth (MIC-2 or Ն50% inhibition) relative to control growth provides both excellent reproducibility of results within and between laboratories and differentiation of isolates with "normal" or "wild-type" susceptibilities from glucan synthesis mutant strains with decreased susceptibilities to echinocandins (9,14).…”