Effect of medium composition on results of macrobroth dilution antifungal susceptibility testing of yeasts

Doern, G V; Tubert, Tracy A.; Chapin, Kimberle; Rinaldi, Michael G.

doi:10.1128/jcm.24.4.507-511.1986

Cited by 52 publications

(13 citation statements)

References 15 publications

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“…Armelles (2) reported no significant difference in the MICs of ketoconazole, miconazole, and econazole determined in either BYNB or SAAMF by broth macrodilution. Some investigators previously showed that MICs were higher for AMB but lower for 5FC when determined in BYNB compared with other media (5). In contrast, using broth microdilution, we found the MIC50s of AMB in BYNB to be twoto eightfold lower than those in other media, while the MIC50s of 5FC were similar in all media.…”

Section: Discussioncontrasting

confidence: 82%

Collaborative investigation of broth microdilution and semisolid agar dilution for in vitro susceptibility testing of Candida albicans

et al. 1992

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A study was performed in two laboratories to evaluate the effect of growth medium and test methodology on interand intralaboratory variations in the MICs of amphotericin B (AMB), flucytosine (5FC), fluconazole (FLU), itraconazole (ITRA), and the triazole Sch 39304 (SCH) against 14 isolates of Candida albicans. Testing was performed by broth microdilution and semisolid agar dilution with the following media, buffered to pH 7.0 with morpholinepropanesulfonic acid (MOPS): buffered yeast nitrogen base (BYNB), Eagle's minimal essential medium (EMEM), RPMI 1640 medium (RPMI), and synthetic amino acid medium for fungi (SAAMF). Inocula were standardized spectrophotometrically, and endpoints were defined by the complete absence of growth for AMB and by no more than 25% of the growth in the drug-free control for all other agents. Comparative analyses of median MICs, as determined by each test method, were made for all drug-medium combinations. Both methods yielded similar (±1 twofold dilution) median MICs for AMB in EMEM and RPMI, 5FC in all media, and FLU in EMEM, RPMI, and SAAMF. In contrast, substantial between-method variations in median MICs were seen for AMB in BYNB and SAAMF, FLU in BYNB, and ITRA and SCH in all media. Interlaboratory concordance of median MICs was good for AMB, 5FC, and FLU but poor for fTRA and SCH in all media. Endpoint determinations were analyzed by use of kappa statistical analyses for evaluating the strength of observer agreement. Moderate to almost perfect interlaboratory agreement occurred with AMB and 5FC in all media and with FLU in EMEM, RPMI, and SAAMF, irrespective of the test method. Slight to almost perfect interlaboratory agreement occurred with ITRA and SCH in EMEM, RPMI, and SAAMF when tested by semisolid agar dilution but not broth microdilution. Kappa values assessing intralaboratory agreement between methods were high for 5FC in all media, for AMB in BYNB, EMEM, and RPMI, and for FLU in EMEM, RPMI, and SAAMF. One laboratory, but not the other, reported substantial to almost perfect agreement between methods for ITRA and SCH in EMEM, RPMI, and SAAMF. Both laboratories reported poor agreement between methods for the azoles in BYNB. Discrepancies noted in azole-BYNB combinations were largely due to the greater inhibitory effect of these agents in BYNB than in other media. These results indicate that the semisolid agar dilution and broth microdilution methods with EMEM or RPMI yield equivalent and reproducible MICs for AMB, 5FC, and FLU but not ITRA and SCH.

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Section: Discussioncontrasting

confidence: 82%

Collaborative investigation of broth microdilution and semisolid agar dilution for in vitro susceptibility testing of Candida albicans

et al. 1992

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“…Broth dilution testing of Candida albicans susceptibility to azole antifungal agents has been difficult because of a number of poorly controlled sources of test variation. The major sources of susceptibility test variation for fluconazole and other azoles in vitro have been reported to be the pH, the composition of the test medium, the inoculum size, and the temperature and duration of incubation (2,6,8,9,11,12,(14)(15)(16)(17)(18)). These factors have been the focus of a series of collaborative studies by the National Committee for Clinical Laboratory Standards (NCCLS) Subcommittee on Antifungal Susceptibility Tests (1,3,5,7,12,16).…”

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confidence: 99%

Comparative evaluation of alternative methods for broth dilution susceptibility testing of fluconazole against Candida albicans

et al. 1994

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A comparative evaluation of methods for broth macro-and microdilution susceptibility testing of fluconazole was conducted with 119 clinical isolates of Candida albicans. Macro-and microdilution testing were performed according to National Committee for Clinical Laboratory Standards recommendations. For reference macrodilution testing, an 80% inhibition endpoint (MIC 80%o) was determined after 48 h of incubation in accordance with National Committee for Clinical Laboratory Standards proposed standard M27-P. Microdilution endpoints were scored as the first tube or well in which a prominent reduction in turbidity (score 2 out of a possible 4) was observed compared with the growth control (Micro MIC-2). Alternative endpoint criteria were assessed independently of the reference MIC 80%o and Micro MIC-2 values and included a colorimetric microdilution endpoint determined by using an oxidation-reduction indicator (Alamar Blue; Alamar Biosciences Inc., Sacramento, Calif.). The MICs for the two microdilution test systems were read after 24 and 48 h of incubation. The percentage of fluconazole MICs within 2 doubling dilutions of the macrodilution reference values was 94% for both microdilution tests read at 24 h. Agreement was slightly lower at 48 h and ranged from 91 to 93%. Comparison of Micro MIC-2 and colorimetric microdilution MICs resulted in agreements of 97 and 93% at 24 and 48 h, respectively. These results show excellent agreement among alternative methods for fluconazole susceptibility testing.

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“…The differences between the methods did not allow an analysis-in-depth of the results because the MIC test is highly dependent of factors such as the inoculum concentration, chemical composition of the medium, pH, temperature, and incubation time. 6,7,16,28,30,34 The results found in this work showed that it is possible to compare the degree of susceptibility to each antifungal drug but without compare the MICs. To compare the MIC values, it is necessary an agreement for the drug concentrations to be tested in both methods because the Etest ® have a broader range for drug concentrations than the broth Microdilution test.…”

Section: Resultsmentioning

confidence: 83%

Comparação da técnica de microdiluição em caldo e ETEST para o cetoconazol frente à Malassezia pachydermatis

Nascente

Cleff

Meinerz

et al. 2009

Braz. J. Vet. Res. Anim. Sci.

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Malassezia pachydermatis is recognized as a normal inhabitant and an opportunistic pathogen of the external ear canal and skin of dogs and cats. In special clinical conditions, and mainly in the cases of therapeutic failure related to external otitis and dermatitis complicated by this yeast, is recommended testing susceptibility to antifungal drugs. Different approaches of evaluating the susceptibility of yeasts faced to antifungals in laboratory exist, some of them are commercial approaches and others previously standardized by the CLSI (NCCLS, 2002). The purpose of this study was to evaluate the susceptibility of 17 samples of M. pachydermatis from canine external otitis using two different in vitro antifungal susceptibility methods: the Etest ® and the broth Microdilution Method (MD) with ketoconazole. The mean MIC observed between the 17 samples were 0.103mg/mL to ETEST and 0.0012mg/mL to MD ranging from 0.004 to 0.75mg/ mL in ETEST and 0.0019 and 0.03mg/mL in MD using the same samples. By ETEST, two (11.8%) samples were resistant, eight (47.1%) susceptible and seven (41.1%) showed intermediate susceptibility. Through the MD it was observed four (23.5%) resistant samples, seven (41.2%) susceptible and six (35.3%) samples with intermediate susceptibility. Despite of the percentages being equivalent in each rank of susceptibility through the two techniques, the results do not correspond to the same sample. These results showed that there is an urgent need to standardize those values considered as parameters for growth inhibition of this yeast. Then a simple and efficient method could be used routinely in the laboratory practice.

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Effect of medium composition on results of macrobroth dilution antifungal susceptibility testing of yeasts

Cited by 52 publications

References 15 publications

Collaborative investigation of broth microdilution and semisolid agar dilution for in vitro susceptibility testing of Candida albicans

Collaborative investigation of broth microdilution and semisolid agar dilution for in vitro susceptibility testing of Candida albicans

Comparative evaluation of alternative methods for broth dilution susceptibility testing of fluconazole against Candida albicans

Comparação da técnica de microdiluição em caldo e ETEST para o cetoconazol frente à Malassezia pachydermatis

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