Colorimetric Microdilution Method Research Articles

Implication of genotypes for prognosis of Candida glabrata bloodstream infections.

Genotyping isolates of a specific pathogen may demonstrate unique patterns of antimicrobial resistance, virulence or outcomes. However, evidence for genotype-outcome association in Candida glabrata is scarce. We aimed to characterize the mycological and clinical relevance of genotypes on C. glabrata bloodstream infections (BSIs). Non-duplicated C. glabrata blood isolates from hospitalized adults were genotyped by MLST, and further clustered by the unweighted pair group method with arithmetic averages (UPGMA). A clonal complex (CC) was defined by UPGMA similarities of >90%. Antifungal susceptibility testing was performed by a colorimetric microdilution method and interpreted following CLSI criteria. Of 48 blood isolates evaluated, 13 STs were identified. CC7 was the leading CC (n = 14; 29.2%), including 13 ST7. The overall fluconazole and echinocandin resistance rates were 6.6% and 0%, respectively. No specific resistance patterns were associated with CC7 or other CCs. Charlson comorbidity index (adjusted OR, 1.49; 95% CI, 1.05-3.11) was the only predictor for CC7. By multivariable Cox regression analyses, CC7 was independently associated with 28 day mortality [adjusted HR (aHR), 3.28; 95% CI, 1.31-8.23], even after considering potential interaction with neutropenia (aHR, 3.41; 95% CI, 1.23-9.42; P for interaction, 0.24) or limited to 34 patients with monomicrobial BSIs (aHR, 2.85; 95% CI, 1.15-7.08). Also, the Kaplan-Meier estimate showed greater mortality with CC7 (P = 0.003). Fluconazole resistance or echinocandin therapy had no significant impact on mortality. Our data suggested comorbid patients were at risk of developing CC7 BSIs. Further, CC7 was independently associated with worse outcomes.

Antifungal susceptibility of clinically isolated invasive Candida tropicalis in East China from 2017 to 2021

Objective: To explore the epidemiological characteristics of sample distribution and antifungal susceptibilities of clinically invasive C. tropicalis isolates from 2017 to 2021 in East China. Methods: Using a retrospective analysis, the East China Invasive Fungal Infection Group (ECIFIG) collected C. tropicalis clinically isolated from 32 hospitals in East China between January 2017 and December 2021. The identification results of the strains were reviewed using mass spectrometry by the central laboratory of the Shanghai East Hospital. The minimum inhibitory concentrations (MICs) of the strains against fluconazole (FLU), voriconazole (VOR), itraconazole (ITR), Posaconazole (POS), isavuconazole (ISA), anidulafungin (ANI), caspofungin (CAS), micafungin (MICA) and 5-fluorocytosine (FCT) were tested by the ThermoFisher CMC1JHY colorimetric microdilution method. The MIC of amphotericin B (AMB) was tested by the broth microdilution method. The MIC results were analyzed based on the clinical breakpoints and epidemiological cutoff values (ECV) published by the Clinical and Laboratory Standards Institute (CLSI) M27 Ed3 and M57 Ed4 documents. Data analysis was conducted using the Kruskal-Wallis test and paired t-test. Results: In total, 305 C. tropicalis isolates were collected. There were 38.0% (116/305) strains isolated from blood, 11.5% (35/305) ascites, 8.9% (27/305) catheter and 8.9% (27/305) drainage fluid. The resistance rate of C. tropicalis to FLU was 32.5%, to VOR was 28.5%, and the cross-resistance rate to FLU and VOR was 28.5%. The wild-type proportions for ITR and POS were 79.3% and 29.2% respectively. There was no significant difference in resistance rates, MIC50, and MIC90 of FLU and VOR, or in the wild-type rates of ITR and POS over five years. More than 95.0% of the isolates were susceptible to echinocandins. However, one strain was identified as being multi-drug resistant. In azole antifungals, voriconazole, itraconazole, posaconazole, and isavuconazole have similar GM MIC values. The GM MIC of fluconazole is significantly higher than that of itraconazole (t=9.95, P<0.05), posaconazole (t=9.99, P<0.05), and voriconazole (t=10.01, P<0.05), Meanwhile, among echinocandins, the GM MIC of ANI was comparable to that of CAS (t=1.17, P>0.05), both of which were significantly higher than MICA (t=11.56, P<0.05; t=4.15, P<0.05). Conclusion: The clinical isolates of C. tropicalis in East China from 2017 to 2021 were relatively susceptible to echinocandins. However, there was consistently high resistance to fluconazole and voriconazole. More intensive efforts should be made on the monitoring of drug resistance in C. tropicalis.

Molecular identification, virulence factors and antifungal susceptibility patterns of Candida parapsilosis complex species isolated from clinical samples.

The aim of this study was to identify C. parapsilosis complex strains isolated from various clinical samples by sequence analysis and to investigate whether there are any differences between the species in terms of virulence factors and antifungal susceptibility. The study included a total of 42 isolates identified as C. parapsilosis complex based on the color they formed in chromogenic medium, colony morphology, and microscopic appearance in Corn Meal-Tween 80 Agar and they were confirmed with API 20 C AUX. For the DNA sequence analysis of clinical isolates, V9G forward and LS reverse primers were used as well as internal transcribed spacers (ITS1 and ITS4). Biofilm formation, esterase, phospholipase, and protease activities were evaluated as virulence factors. Antifungal susceptibility was investigated via colorimetric microdilution method. A total of 75 non-C. albicans isolates were obtained from various clinical samples between 2016 and 2017 in a Turkish Tertiary Care Hospital. Of them, 42 were identified as members of the C. parapsilosis complex. Of the 42 strains, 41 were identified as C. parapsilosis sensu stricto (CpSS), while only one was identified as C. orthopsilosis. Of the CpSS strains, 31 (75.6%) were biofilm-positive, six (14.6%) were esterase-positive, nine (21.9%) were positive for phospholipase activity, and 31 (75.6%) were positive for protease formation, whereas all virulence factors of C. orthopsilosis strain were found to be negative. All CpSS strains were found susceptible to amphotericin B, echinocandins, and flucytosine. It has been concluded that the use of molecular methods to identify CpSS would not be effective in routine laboratory practices as it is the most commonly isolated species from the C. parapsilosis complex and there are no significant differences between species in terms of antifungal susceptibility.

Antifungal susceptibility of clinical mould isolates in New Zealand, 2001–2019

The objective of this study was to review the antifungal susceptibility of clinical mould isolates performed by the New Zealand Mycology Reference Laboratory. Isolates were either local or referred for testing from other New Zealand laboratories. All isolates were tested by the broth colorimetric microdilution method, Sensititre YeastOne (SYO). Epidemiological cut-off values (ECVs) derived from either the Clinical and Laboratory Standards Institute (CLSI) method or SYO were used to determine the proportion of non-wild type (non-WT) isolates, i.e., those with an increased likelihood to harbour acquired mechanisms of resistance. A total of 614 isolates were tested. Most isolates (55%) were from the respiratory tract followed by musculoskeletal tissue (17%), eye (10%) and abdomen (5%). The azoles had similar activity except for voriconazole which was less active against the Mucorales. The echinocandins had good activity against Aspergillus spp., other hyaline moulds and dematiaceous isolates but were inactive against Fusarium spp., Lomentospora prolificans and the Mucorales. Amphotericin B had best activity against the Mucorales. The two least susceptible groups were Fusarium spp. and L.prolificans isolates. Three Aspergillus isolates were non-WT for amphotericin B, and four non-WT for azoles. Non-WT were not encountered for caspofungin. Non-Aspergillus isolates in New Zealand have susceptibility patterns similar to those reported elsewhere. In contrast to a growing number of other countries, azole resistance was rare in A.fumigatus sensu stricto. Non-WT isolates were uncommon. The results provide a baseline for monitoring emerging antifungal resistance in New Zealand and support current Australasian treatment guidelines for invasive fungal infections.

Antibacterial activity of methanol extracts of the leaves of\xa0three medicinal plants against selected bacteria isolated from wounds of lymphoedema patients

BackgroundPatients with lymphoedema are at high risk of getting bacterial and fungal wound infections leading to acute inflammatory episodes associated with cellulitis and erysipelas. In Ethiopia, wound infections are traditionally treated with medicinal plants.MethodsAgar well diffusion and colorimetric microdilution methods were used to determine the antibacterial activity of methanol extracts of the three medicinal plants against Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Shewanella alage, methicillin-resistant S. aureus ATCC®43300TM, Staphylococcus aureus ATCC25923, Escherichia coli ATCC25922, Klebsiella pneumoniae ATCC700603, and Pseudomonas aeruginosa ATCC37853.ResultsThe methanol extract of L. inermis leaves showed high activity against all tested bacterial species, which was comparable to the standard drugs. Similarly, the extracts of A. indica showed activity against all tested species though at higher concentrations, and higher activity was recorded against Streptococcus pyogenes isolates at all concentrations. However, the extract of A. aspera showed the lowest activity against all tested species except Streptococcus pyogenes isolates. The lowest minimum inhibitory concentration (MIC) was recorded with the extract of L. inermis against E. coli isolate and S. aureus ATCC 25923.ConclusionMethanol extracts of L. inermis, A. indica, and A. aspera leaves exhibited antimicrobial activity against selected bacterial isolates involved in wound infections, of which the methanol extracts of L. inermis exhibited the highest activity. The results of the present study support the traditional use of plants against microbial infections, which could potentially be exploited for the treatment of wound infections associated with lymphoedema.

Antileishmanial Potentialities of Croton linearis Leaf Essential Oil

The essential oil was obtained from Croton linearis Jacq. leaves. Its chemical composition was analyzed by Gas Chromatography-Mass Spectrometry. A total of 82 compounds were identified, being the principal components: guaiol (7.93%); eudesma-4(15),7-dien-1β-ol (4.94%) and guaia-3,10(14)-dien-11-ol (4.52%). Antimicrobial activity was determined against six Candida spp., three bacteria ( Staphylococcus aureus, Escherichia coli and Pseudomona aeruginosa) and two parasites ( Leishmania amazonensis and Trypanosoma cruzi). The selectivity index (SI) was computed through the determination of it cytotoxicity on peritoneal macrophages from BALB/c mice and murine fibroblasts L929 cells. Colorimetric microdilution methods as well as direct counting in optical microscopes were performed. The essential oil showed remarkable activity against L. amazonensis (IC50Promastigote: 20.0 ± 4.9 μg/mL; IC50Amastigote: 13.8 ± 4.3 μg/mL), moderate activity against T. cruzi (IC50Trypomastigote: 197.26 ± 8.7 μg/mL) and weak activity against P. aureginosa. Cytotoxicity values were CC50= 89.1 ± 3.4 μg/mL for macrophages BALB/c and CC50= 306 ± 110 μg/mL for L929 cells, rendering a SI of 6 for amastigote form of L. amazonensis. Croton linearis Jacq. leaf essential oil, therefore, could be a potential candidate for future investigations regarding Leishmaniasis treatment.

Differences in antibacterial effectiveness between the whole extract and high-performance liquid chromatography-separated constituents from the cultivated mushroom Agaricus bisporus

There is inadequate data regarding how components interact in the whole extract of mushrooms to confer antibacterial activities. This study evaluated differences in the antibacterial capability (both potency and spectrum of action) between the crude extract, an EtOAc/MeOH fraction, and reverse-phase high performance liquid chromatography (RP-HPLC)-separated constituents from the cultivated button mushroom using a colorimetric micro-dilution method. The total extract showed excellent activities at doses < 1 mg/mL towards Bacillus subtilis only. In contrast, the fraction inhibited a more range of the tested bacteria at concentrations higher than did the extract (p < 0.05). The only active HPLC-separated compound exhibited degrees of inhibition against all the Gram-negative and Gram-positive bacteria at concentrations higher than 5 mg/mL. These findings may point to antibacterial synergism in the crude extract, implying high nutritional values for the whole mushroom as a functional food. Conversely, the broader spectrum of action of individual components warrants further investigations to determine its efficacy against antibiotic-resistant or Gram-negative bacteria in combination with commercial antibiotics.

Unraveling the antifungal activity of a South American rattlesnake toxin crotamine

Crotamine is a highly basic peptide from the venom of Crotalus durissus terrificus rattlesnake. Its common gene ancestry and structural similarity with the β-defensins, mainly due to an identical disulfide bond pattern, stimulated us to assess the antimicrobial properties of native, recombinant, and chemically synthesized crotamine. Antimicrobial activities against standard strains and clinical isolates were analyzed by the colorimetric microdilution method showing a weak antibacterial activity against both Gram-positive and Gram-negative bacteria [MIC (Minimum Inhibitory Concentration) of 50->200 μg/mL], with the exception of Micrococcus luteus [MIC ranging from 1 to 2 μg/mL]. No detectable activity was observed for the filamentous fungus Aspergillus fumigatus and Trichophyton rubrum at concentrations up to 125 μg/mL. However, a pronounced antifungal activity against Candida spp., Trichosporon spp., and Cryptococcus neoformans [12.5-50.0 μg/mL] was observed. Chemically produced synthetic crotamine in general displayed MIC values similar to those observed for native crotamine, whereas recombinant crotamine was overridingly more potent in most assays. On the other hand, derived short linear peptides were not very effective apart from a few exceptions. Pronounced ultrastructure alteration in Candida albicans elicited by crotamine was observed by electron microscopy analyses. The peculiar specificity for highly proliferating cells was confirmed here showing potential low cytotoxic effect of crotamine against nontumoral mammal cell lines (HEK293, PC12, and primary culture astrocyte cells) compared to tumoral B16F10 cells, and no hemolytic activity was observed. Taken together these results suggest that, at low concentration, crotamine is a potentially valuable anti-yeast or candicidal agent, with low harmful effects on normal mammal cells, justifying further studies on its mechanisms of action aiming medical and industrial applications.

Antimicrobial activity of crude extracts from mangrove fungal endophytes

The aim of this work was to select endophytic fungi from mangrove plants that produced antimicrobial substances. Minimal inhibitory concentrations (MIC) and minimal bactericidal concentrations (MBC) or minimal fungicidal concentrations (MFC) of crude extracts from 150 isolates were determined against potential human pathogens by a colorimetric microdilution method. Ninety-two isolates (61.3%) produced inhibitory compounds. Most of the extracts (28–32%) inhibited Staphylococcus aureus (MIC/MBC 4–200/64–200 μg ml−1). Only two extracts inhibited Pseudomonas aeruginosa (MIC/MBC 200/>200 μg ml−1). 25.5 and 11.7% inhibited Microsporum gypseum and Cryptococcus neoformans (MIC/MFC 4–200/8–200 μg ml−1 and 8–200/8–200 μg ml−1, respectively), while 7.5% were active against Candida albicans (MIC/MFC 32–200/32–200 μg ml−1). None of the extracts inhibited Escherichia coli. The most active fungal extracts were from six genera, Acremonium, Diaporthe, Hypoxylon, Pestalotiopsis, Phomopsis, and Xylaria as identified using morphological and molecular methods. Phomopsis sp. MA194 (GU592007, GU592018) isolated from Rhizophora apiculata showed the broadest antimicrobial spectrum with low MIC values of 8–32 μg ml−1against Gram-positive bacteria, yeasts and M. gypseum. It was concluded that endophytic fungi from mangrove plants are diverse, many produce compounds with antimicrobial activity and could be suitable sources of new antimicrobial natural products.

In vitro antifungal susceptibility testing of filamentous fungi with Sensititre Yeast OneTM

Sensititre is a colorimetric microdilution method for in vitro antifungal susceptibility testing based on the M27-A document (National Committee for Clinical Laboratory Standards) for yeasts. Difference between both methods is the presence of Alamar-blue and RPMI 1640 (glucose 2%) as culture medium. Antifungal susceptibility to amphotericin B, fluconazole, itraconazole, ketoconazole and flucytosine, 100 opportunistic filamentous fungi (Aspergillus spp., Fusarium spp., Scedosporium spp.) obtained from pathological samples was determined by the Sensititre method. Induction to conidium and sporangiospore formation at 35 degrees C was used to get inoculum and plates were covered by 1 ml of saline and suspensions were made by gently probing by a sterile loop. Optical densities of the conidial suspensions were adjusted to 80-82% transmittance for Aspergillus spp. and 68-70% for the rest of strains tested. Final inoculum concentration size was 0.4 x 10(4)-5 x 10(4) CFU ml(-1). Readings were made at 72 h of incubation at 35 degrees C; amphotericin B and itraconazole was active against Aspergillus fumigatus with CMI90 1 and 0.5 microg ml(-1), respectively, opposite to Scedosporium prolificans and Scedosporium apiospermum. As it was expected, a CMI90 of 256 microg ml(-1) for fluconazole and CMI90 for flucytosine amounting to 64 g ml(-1) were obtained. Sensititre Yeast One is a useful method and an alternative to reference methods to determine antifungal susceptibility of filamentous fungi for clinical laboratory routine. Correlation with microdilution results is studied. New triazole derivatives should be included as soon as their clinical use will be feasible.

In vitro susceptibility of Cryptococcus neoformans clinical isolates from Egypt to seven antifungal drugs

The in vitro susceptibility of 29 clinical isolates of Cryptococcus neoformans to fluconazole, miconazole, itraconazole, ketoconazole, flucytosine, nystatin and amphotericin B was tested by broth and colorimetric microdilution methods. Most of the isolates showed uniform patterns of susceptibility to the used antifungal agents. Only three isolates exhibited resistance [fourfold or greater rise in the minimum inhibitory concentrations (MICs)] to the tested antifungal drugs. The MIC50 and MIC90 were 0.5-8 mg l(-1) for 5-flucytosine, 0.2-8.25 mg l(-1) for nystatin, 0.5-16 mg l(-1) for fluconazole and 0.2-12.5 mg l(-1) for miconazole. However, MIC50 and MIC90 were in narrow range for the clinical yeast isolates in both methods used and showed 0.5-1 mg l(-1) for amphotericin B and 0.016-0.25 mg l(-1) for both ketoconazole and itraconazole. The combination of fluconazole plus flucytosine showed greater synergistic and fungicidal activity compared with that of fluconazole plus amphotericin B or the use of individual drugs.

Antifungal Activity of Amphotericin B and Itraconazole against Filamentous Fungi: Comparison of the Sensititre Yeast OneŴ and NCCLS M38-A Reference Methods

The susceptibilities of 81 clinical isolates of Aspergillus spp.Fusarium spp., and Scedosporium spp., to amphotericin B and itraconazole were determined by the colorimetric microdilution method Sensititre® and the reference microdilution method of NCCLS standard M38-A for filamentous fungi. No major discrepancies were found and agreement ranged between 86.4% to 84% and 69.1% to 86.4% for amphotericin B and itraconazole respectively at 48 h and 72 h of incubation by using the recommended endpoints. Within two two-fold dilutions, high levels of agreement were found in general for amphotericin B at 48 or 72 h (86.4 to 87.7%) and itraconazole (91.4 to 93.8%). Relatively better agreement was found for itraconazole at 72 h of incubation and 48 for amphotericin B.

In Vitro Activities of Fluoroquinolones against the SpirocheteBorrelia burgdorferi

Little is known to date about the in vitro activity of fluoroquinolones against Borrelia species. Our study aimed at determining the in vitro activities of 15 quinolones against nine isolates of the Borrelia burgdorferi sensu lato complex in addition to one Borrelia valaisiana and one Borrelia bissettii tick isolate. For the determination of MICs, a standardized colorimetric microdilution method was applied. Determination of minimal borreliacidal concentrations providing 100% killing of the final inoculum (MBCs) after 72 h and time-kill experiments were performed by conventional culture in Barbour-Stoenner-Kelly medium in combination with dark-field microscopy. The rank order of potency on a microgram-per-milliliter basis for the substances with in vitro activity against B. burgdorferi was gemifloxacin (MIC at which 90% of the isolates tested are inhibited [MIC(90)], 0.12 microg/ml) > sitafloxacin (MIC(90), 0.5 microg/ml), grepafloxacin (MIC(90), 0.5 microg/ml) > gatifloxacin (MIC(90), 1 microg/ml), sparfloxacin (MIC(90), 1 microg/ml), trovafloxacin (MIC(90), 1 microg/ml) > moxifloxacin (MIC(90), 2 microg/ml), ciprofloxacin (MIC(90), 2 microg/ml) > levofloxacin (MIC(90), 4 microg/ml) > ofloxacin (MIC(90), 8 microg/ml), norfloxacin (MIC(90), 8 microg/ml) > fleroxacin (MIC(90), >16 microg/ml), and pefloxacin (MIC(90), 32 microg/ml) > nalidixic acid (MIC(90), 256 microg/ml). After 72 h of exposure, gemifloxacin was borreliacidal (100% killing) against the isolates investigated at a median MBC of 4 microg/ml. In the other compounds tested, median MBCs were higher (> or =8 microg/ml). Results of electron microscopy and time-kill studies clearly support an in vitro activity of some fluoroquinolones against borreliae. Our study demonstrates for the first time the enhanced in vitro effectiveness of some of the recently introduced 4-quinolones against B. burgdorferi.

In vitro activity of mezlocillin, meropenem, aztreonam, vancomycin, teicoplanin, ribostamycin and fusidic acid against Borrelia burgdorferi

The in vitro susceptibility profile of Borrelia burgdorferi is not yet well defined for several antibiotics. Our study explored the in vitro susceptibility of B. burgdorferi to mezlocillin, meropenem, aztreonam, vancomycin, teicoplanin, ribostamycin and fusidic acid. Minimal inhibitory concentrations (MICs) and minimal borreliacidal concentrations (MBCs) were measured using a standardised colorimetric microdilution method and conventional subculture experiments. MIC values were lowest for mezlocillin (MIC 90, ≤0.06 mg/l) and meropenem (MIC 90, 0.33 mg/l). Vancomycin (MIC 90, 0.83 mg/l) was less effective in vitro. Borreliae proved to be resistant to aztreonam (MIC 90, >32 mg/l), teicoplanin (MIC 90, 6.6 mg/l), ribostamycin (MIC 90, 32 mg/l), and fusidic acid (MIC 90, >4 mg/l). The mean MBCs resulting in 100% killing of the final inoculum after 72 h of incubation were lowest for mezlocillin (MBC, 0.83 mg/l). This study gathered further data on the in vitro susceptibility patterns of the B. burgdorferi complex. The excellent in vitro effectiveness of acylamino-penicillin derivatives and their suitability for the therapy of Lyme disease is emphasised.

New colorimetric microdilution method for in vitro susceptibility testing of Borrelia burgdorferi against antimicrobial substances.

A newly developed colorimetric microdilution method was used to analyze the activity of 12 antimicrobial agents against nine Borrelia burgdorferi isolates, including all three genospecies pathogenic for humans. In addition, in vitro antimicrobial resistance patterns of Borrelia valaisiana and Borrelia bissettii tick isolates were investigated. The applied test system is based upon color changes that occur in the presence of phenol red and result from the accumulation of nonvolatile acid produced by actively metabolizing spirochetes. After 72 h of incubation, minimal inhibitory concentrations (MICs) were determined from the decrease of absorbance by software-assisted calculation of growth curves. MIC values were lowest for azlocillin (MIC, < or = 0.125 microg/ml), ceftriaxone (MIC range, < or = 0.015-0.06 microg/ ml), and azithromycin (MIC range, < or = 0.015-0.06 microg/ml). Whereas tobramycin (MIC range, 8-64 microg/ml) exhibited little activity, spectinomycin (MIC range, 0.25-2 microg/ml) showed in vitro antimicrobial activity against Borrelia burgdorferi. The MICs of penicillin G for Borrelia afzelii isolates were ten times higher than those for Borrelia burgdorferi, Borrelia valaisiana, and Borrelia bissettii isolates (P<0.05) and 100 times higher than those for isolates belonging to the genospecies Borrelia garinii (P < 0.05). Further significant differences with respect to the MIC values of the other antimicrobial agents tested were not noted. The colorimetric microdilution method offered the advantages of reliability, reproducibility, and convenience and could handle large numbers of isolates and antibiotics.

Multisite reproducibility of colorimetric broth microdilution method for antifungal susceptibility testing of yeast isolates

MICs of fluconazole and amphotericin B were determined independently for 100 coded yeast isolates by each of six laboratories to determine reproducibility of results by using a colorimetric oxidation-reduction-based broth microdilution test. In addition, each site tested five quality control isolates on at least four different occasions during the study. Results agreed within a three-dilution range (mode +/- 1 log2 dilution) for 96.2% of fluconazole tests and 92.7% of amphotericin B tests. Agreement among tests with the quality control isolates was 99.4% with fluconazole and 98.6% with amphotericin B. These results indicate that the colorimetric microdilution method is reproducible among laboratories.

Multicenter comparison of a colorimetric microdilution broth method with the reference macrodilution method for in vitro susceptibility testing of yeast isolates

This multicenter study was performed to compare a colorimetric microdilution method with the NCCLS M27-P reference macrodilution method for the testing of yeast isolates against amphotericin B, fluconazole, and 5-fluorocytosine (5FC). Testing was performed on ten yeast isolates in five independent laboratories. All sites tested each isolate a total of 20 times with both methods. MICs were read after 48 h incubation. The macrodilution MIC reference range was defined as the modal MIC +/- 1-log2 dilution for each organism-antifungal agent combination. Agreement between the M27-P reference range results and the microdilution MICs was 86% with amphotericin B, 90% with fluconazole, and 93% with 5FC. Based on these data, it is apparent that new approaches, such as the colorimetric microdilution method, will provide MIC values comparable to the M27-P macrodilution method in a format that is more practical for use in a busy clinical laboratory.