In vitro susceptibilities of bloodstream isolates of Candida species to six antifungal agents: results from a population-based active surveillance programme, Barcelona, Spain, 2002-2003

OBJECTIVES: The antifungal drug susceptibilities of 351 isolates of Candida species, obtained through active laboratory-based surveillance in the period January 2002-December 2003, were determined (Candida albicans 51%, Candida parapsilosis 23%, Candida tropicalis 10%, Candida glabrata 9%, Candida krusei 4%). METHODS: The MICs of amphotericin B, flucytosine, fluconazole, itraconazole, voriconazole and caspofungin were established by means of the broth microdilution reference procedure of the European Committee on Antibiotic Susceptibility Testing. RESULTS AND CONCLUSIONS: Amphotericin B and flucytosine were active in vitro against all strains. A total of 24 isolates (6.8%) showed decreased susceptibility to fluconazole (MIC > or = 16 mg/L) and 43 (12.3%) showed decreased susceptibility to itraconazole (MIC > or = 0.25 mg/L). Voriconazole and caspofungin were active in vitro against the majority of isolates, even those that were resistant to fluconazole.     

Azasordarins: susceptibility of fluconazole-susceptible and fluconazole-resistant clinical isolates of Candida spp. to GW 471558

The in vitro activity of the azasordarin GW 471558 was compared with those of amphotericin B, flucytosine, itraconazole, and ketoconazole against 177 clinical isolates of Candida spp. GW 471558 showed potent activity against Candida albicans, Candida glabrata, and Candida tropicalis, even against isolates with decreased susceptibility to azoles. Candida krusei, Candida parapsilosis, Candida lusitaniae, and Candida guilliermondii are resistant to GW 471558 in vitro (MICs, >128 microg/ml).     

In-vitro activity of five antifungal agents against uncommon clinical isolates of Candida spp

A broth microdilution method and an agar dilution method were used for testing fluconazole, itraconazole, ketoconazole, flucytosine and amphotericin B against 98 clinical isolates belonging to seven species of Candida. The approximate rank order of fluconazole MICs was Candida lusitaniae approximately Candida kefyr < Candida famata approximately Candida guilliermondii < Candida pelliculosa approximately C. lipolytica approximately Candida inconspicua. Candida lypolitica and C. pelliculosa were the species least susceptible to itraconazole and ketoconazole. Flucytosine MICs revealed the highest prevalence of resistant strains among C. lipolytica and C. lusitaniae. All isolates were susceptible to amphotericin B.     

In vitro activities of isavuconazole and other antifungal agents against Candida bloodstream isolates

Isavuconazole is the active component of the new azole antifungal agent BAL8557, which is entering phase III clinical development. This study was conducted to compare the in vitro activities of isavuconazole and five other antifungal agents against 296 Candida isolates that were recovered consecutively from blood cultures between 1995 and 2004 at a tertiary care university hospital. Microdilution testing was done in accordance with CLSI (formerly NCCLS) guideline M27-A2 in RPMI-1640 MOPS (morpholinepropanesulfonic acid) broth. The antifungal agents tested were amphotericin B, flucytosine, fluconazole, itraconazole, voriconazole, and isavuconazole. C. albicans was the most common species, representing 57.1% of all isolates. There was no trend found in favor of non-Candida albicans species over time. In terms of MIC(50)s, isavuconazole was more active (0.004 mg/liter) than amphotericin B (0.5 mg/liter), itraconazole (0.008 mg/liter), voriconazole (0.03 mg/liter), flucytosine (0.125 mg/liter), and fluconazole (8 mg/liter). For isavuconazole, MIC(50)s/MIC(90)s ranged from 000.2/0.004 mg/liter for C. albicans to 0.25/0.5 mg/liter for C. glabrata. Two percent of isolates (C. glabrata and C. krusei) were resistant to fluconazole; C. albicans strains resistant to fluconazole were not detected. There were only two isolates with MICs for isavuconazole that were >0.5 mg/liter: both were C. glabrata isolates, and the MICs were 2 and 4 mg/liter, respectively. In conclusion, isavuconazole is highly active against Candida bloodstream isolates, including fluconazole-resistant strains. It was more active than itraconazole and voriconazole against C. albicans and C. glabrata and appears to be a promising agent against systemic Candida infections.     

Activity of a new triazole, Sch 56592, compared with those of four other antifungal agents tested against clinical isolates of Candida spp. and Saccharomyces cerevisiae.

Sch 56592 is a new triazole agent with potent, broad-spectrum antifungal activity. The in vitro activities of Sch 56592, itraconazole, fluconazole, amphotericin B, and flucytosine (5-FC) against 404 clinical isolates of Candida spp. (382 isolates) and Saccharomyces cerevisiae (22 isolates) were investigated. In vitro susceptibility testing was performed by a broth microdilution method performed according to National Committee for Clinical Laboratory Standards guidelines. Overall, Sch 56592 was very active (MIC at which 90% of isolates are inhibited [MIC90], 0.5 microgram/ml) against these yeast isolates. Sch 56592 was most active against Candida tropicalis, Candida parapsilosis, candida lusitaniae, and Candida stellatoidea (MIC90, < or = 0.12 microgram/ml) and was least active against Candida glabrata (MIC90, 2.0 micrograms/ml). Sch 56592 was 2- to 32-fold more active than amphotericin B and 5-FC against all species except C. glabrata. By comparison with the other triazoles, Sch 56592 was equivalent to itraconazole and greater than or equal to eightfold more active than fluconazole. On the basis of these results, Sch 56592 has promising antifungal activity, and further in vitro and in vivo investigations are warranted.     

Susceptibility of fluconazole-resistant clinical isolates of Candida spp. to echinocandin LY303366, itraconazole and amphotericin B

The in vitro activity of LY303366 was compared with those of itraconazole and amphotericin B against 156 fluconazole-resistant (MIC > or = 16 mg/L) clinical isolates of CANDIDA: spp. An adaptation of the NCCLS reference method was employed for determination of MICs. LY303366 was more potent than either itraconazole or amphotericin B against Candida albicans, Candida glabrata, Candida krusei and Candida tropicalis, even against isolates with itraconazole MICs > or = 1 mg/L. LY303366 was less potent in vitro against Candida parapsilosis and Candida guilliermondii isolates. LY303366 has promising antifungal activity and warrants further investigation.     

Influence of Human Serum on Antifungal Pharmacodynamics with Candida albicans

Antifungal susceptibilities (NCCLS, approved standard M27-A, 1997) were determined for the reference strain ATCC 90028 and 21 clinical isolates of Candida albicans with varying levels of fluconazole susceptibility using RPMI 1640 (RPMI) and 80% fresh human serum-20% RPMI (serum). Sixty-four percent (14 of 22) of the isolates tested demonstrated significant decreases (> or = 4-fold) in fluconazole MICs in the presence of serum, and the remaining eight isolates exhibited no change. Itraconazole and ketoconazole, two highly protein-bound antifungal agents, had MICs in serum that were increased or unchanged for 46% (10 of 22) and 41% (9 of 22) of the isolates, respectively. All 10 isolates tested against an investigational antifungal agent, LY303366, demonstrated significant increases in the MIC required in serum, while differences in amphotericin B MICs in the two media were not observed. Four of 10 isolates tested demonstrated fourfold higher flucytosine MICs in serum than in RPMI. Postantifungal effects (PAFEs) and 24-h kill curves were determined by standard methods for selected isolates. At the MIC, fluconazole, itraconazole, ketoconazole, flucytosine, and LY303366 kill curves and PAFEs in RPMI were similar to those in serum. Isolates of fluconazole-resistant C. albicans required lower MICs in serum than in RPMI, without relative increases in fungal killing or PAFEs. Isolates tested against amphotericin B demonstrated significantly reduced killing and shorter PAFEs in serum than in RPMI without observable changes in MIC. In conclusion, antifungal pharmacodynamics in RPMI did not consistently predict antifungal activity in serum for azoles and amphotericin B. Generally speaking, antifungal agents with high protein binding exhibited some form of reduced activity (MIC, killing, or PAFE) in the presence of serum compared to those with low protein binding.     

Flow cytometry antifungal susceptibility testing of pathogenic yeasts other than Candida albicans and comparison with the NCCLS broth microdilution test

Candida species other than Candida albicans frequently cause nosocomial infections in immunocompromised patients. Some of these pathogens have either variable susceptibility patterns or intrinsic resistance against common azoles. The availability of a rapid and reproducible susceptibility-testing method is likely to help in the selection of an appropriate regimen for therapy. A flow cytometry (FC) method was used in the present study for susceptibility testing of Candida glabrata, Candida guilliermondii, Candida krusei, Candida lusitaniae, Candida parapsilosis, Candida tropicalis, and Cryptococcus neoformans based on accumulation of the DNA binding dye propidium iodide (PI). The results were compared with MIC results obtained for amphotericin B and fluconazole using the NCCLS broth microdilution method (M27-A). For FC, the yeast inoculum was prepared spectrophotometrically, the drugs were diluted in either RPMI 1640 or yeast nitrogen base containing 1% dextrose, and yeast samples and drug dilutions were incubated with amphotericin B and fluconazole, respectively, for 4 to 6 h. Sodium deoxycholate and PI were added at the end of incubation, and fluorescence was measured with a FACScan flow cytometer (Becton Dickinson). The lowest drug concentration that showed a 50% increase in mean channel fluorescence compared to that of the growth control was designated the MIC. All tests were repeated once. The MICs obtained by FC for all yeast isolates except C. lusitaniae were in very good agreement (within 1 dilution) of the results of the NCCLS broth microdilution method. Paired t test values were not statistically significant (P = 0.377 for amphotericin B; P = 0.383 for fluconazole). Exceptionally, C. lusitaniae isolates showed higher MICs (2 dilutions or more) than in the corresponding NCCLS broth microdilution method for amphotericin B. Overall, FC antifungal susceptibility testing provided rapid, reproducible results that were statistically comparable to those obtained with the NCCLS method.     

Antifungal susceptibilities of clinical isolates of Candida species, Cryptococcus neoformans, and Aspergillus species from Taiwan: surveillance of multicenter antimicrobial resistance in Taiwan program data from 2003

The susceptibilities of nonduplicate isolates to six antifungal agents were determined for 391 blood isolates of seven Candida species, 70 clinical isolates (from blood or cerebrospinal fluid) of Cryptococcus neoformans, and 96 clinical isolates of four Aspergillus species, which were collected in seven different hospitals in Taiwan (as part of the 2003 program of the study group Surveillance of Multicenter Antimicrobial Resistance in Taiwan). All isolates of Candida species other than C. glabrata and C. krusei were susceptible to fluconazole. Among the 59 C. glabrata isolates, 16 (27%) were not susceptible to fluconazole, and all were dose-dependently susceptible or resistant to itraconazole. For three (5.1%) C. glabrata isolates, voriconazole MICs were 2 to 4 microg/ml, and for all other Candida species isolates, voriconazole MICs were /=2 microg/ml were 100% (3 isolates) for C. krusei, 11% (23 of 207 isolates) for Candida albicans, 3.0% (2 of 67 isolates) for Candida tropicalis, 20% (12 of 59 isolates) for C. glabrata, and 0% for both Candida parapsilosis and Candida lusitaniae. For three (4%) Cryptococcus neoformans isolates, fluconazole MICs were >/=16 microg/ml, and two (3%) isolates were not inhibited by 1 mug of amphotericin B/ml. For four (4.2%) of the Aspergillus isolates, itraconazole MICs were 8 microg/ml. Aspergillus flavus was less susceptible to amphotericin B, with the MICs at which 50% (1 microg/ml) and 90% (2 microg/ml) nsrsid417869\delrsid7301351 of isolates were inhibited being twofold greater than those for Aspergillus fumigatus and Aspergillus niger. All Aspergillus isolates were inhibited by 相似文献   

Initial results from a longitudinal international surveillance programme for anidulafungin (2003)

OBJECTIVES: This longitudinal study evaluated the in vitro activity of anidulafungin against 880 clinical yeast isolates and 68 mould isolates from 64 medical centres in North America, Latin America and Europe. METHODS: MICs of anidulafungin, amphotericin B, 5-fluorocytosine, fluconazole, itraconazole, ketoconazole and voriconazole were determined using reference method (M27-A2) guidelines. The M38-A reference method was used for the filamentous fungi, including determination of minimum effective concentrations (MECs) of anidulafungin. RESULTS: Anidulafungin was more active when compared with fluconazole and itraconazole for Candida albicans (MIC(90), 0.06 mg/L), Candida tropicalis (MIC(90), 0.06 mg/L), Candida glabrata (MIC(90), 0.12 mg/L), Candida krusei (MIC(90), 0.06 mg/L) and Candida lusitaniae (MIC(90), 1 mg/L) as well as the less-often encountered yeast species. Anidulafungin was less active against Candida parapsilosis, Candida guilliermondii and Candida famata (MIC(50), 1-2 mg/L). Anidulafungin also exhibited excellent activity against all Aspergillus spp. (MEC(90), < or =0.03 mg/L). Anidulafungin was also evaluated comparing two end point reading criteria and two incubation intervals. Data indicate that longer incubation periods do not significantly influence overall MIC ranges. These international surveillance results for anidulafungin confirm the activity observed in studies of smaller numbers of isolates.     

In vitro susceptibility of 245 yeast isolates to amphotericin B, 5-fluorocytosine, ketoconazole, fluconazole and itraconazole.

The in vitro activity of amphotericin B, 5-fluorocytosine, ketoconazole, fluconazole and itraconazole was tested against 245 yeast strains isolated from clinical specimens (68 Candida albicans, 74 Candida tropicalis, 43 Candida krusei, 28 Candida glabrata, 19 Candida parapsilosis, 8 Candida lusitaniae and 5 Candida guilliermondii). An agar dilution method was employed to carry out testing. Minimal inhibitory concentrations to restrain 90% of isolate growth (MIC90) ranged from 0.12 to 2 mg/l for amphotericin B and for 5-fluorocytosine, from 0.03 to 8 mg/l for ketoconazole, from 0.05 to 50 mg/l for itraconazole and from 0.1 to > 100 mg/l for fluconazole. Among the azole derivatives, the most active was ketoconazole, followed by itraconazole. Only 1 strain of C. albicans was resistant to amphotericin B (MIC > 4 mg/l). Both C. tropicalis and C. krusei responded poorly to fluconazole and the former to itraconazole as well. The species most susceptible to the antifungal agents tested was C. glabrata and the most resistant were C. tropicalis and C. krusei.     

In-vitro antifungal activity of liposomal nystatin in comparison with nystatin, amphotericin B cholesteryl sulphate, liposomal amphotericin B, amphotericin B lipid complex, amphotericin B desoxycholate, fluconazole and itraconazole.

The in-vitro susceptibilities of 120 clinical isolates of yeasts to liposomal nystatin were compared with those to amphotericin B lipid complex (ABLC), liposomal amphotericin B (LAB), amphotericin B cholesteryl sulphate (ABCD), amphotericin B desoxycholate, nystatin, fluconazole and itraconazole. Yeast isolates examined included strains of Candida albicans, Candida parapsilosis, Candida glabrata, Candida krusei, Candida guilliermondii, Candida tropicalis, Candida kefyr, Candida viswanathii, Candida famata, Candida rugosa, Rhodotorula rubra, Trichosporon spp., Cryptococcus laurentii and Cryptococcus neoformans. The mean MICs for all strains examined were: liposomal nystatin 0.96 mg/L; nystatin 0.54 mg/L; ABLC 0.65 mg/L; LAB 1.07 mg/L; ABCD 0.75 mg/L; amphotericin B 0.43 mg/L; fluconazole 5.53 mg/L; and itraconazole 0.33 mg/L. No significant differences were seen between the activity of liposomal nystatin and the polyene drugs or itraconazole, but liposomal nystatin was more active than fluconazole. MICs were lower than the reported blood concentrations following therapeutic doses of this drug, indicating the potential for a therapeutic use of liposomal nystatin in humans. These results indicate good activity in vitro against medically important yeasts, which compares favourably with the activities of other currently available antifungal drugs. Liposomal nystatin may have a role in the treatment of disseminated and systemic mycoses.     

In vitro activity of a new pneumocandin antifungal agent, L-733,560 against azole-susceptible and -resistant Candida and Torulopsis species.

The activity of a new water-soluble pneumocandin, L-733,560, was evaluated with 107 pathogenic strains of Candida and Torulopsis, which included 23 strains with known multi-azole resistance patterns. In vitro evaluation of L-733,560 activity was performed by a broth microdilution method, and the activity was compared with the activities of amphotericin B, fluconazole, ketoconazole, itraconazole, and flucytosine. The mean MICs of L-733,560 were 0.15 microgram/ml for C. lusitaniae, 0.72 microgram/ml for C. parapsilosis, 0.78 micrograms/ml for C. krusei, and 1.25 micrograms/ml for C. guilliermondii. The results indicate that the new antifungal agent L-733,560 demonstrated the best activity with the lowest MICs against C. albicans, T. glabrata, C. tropicalis, and C. kefyr, less activity against C. krusei, C. lusitaniae, and C. parapsilosis, and the least activity against C. guilliermondii. L-733,560 also demonstrated good activity against the various multi-azole-resistant Candida and T. glabrata isolates.     

In vitro activities of ravuconazole and voriconazole compared with those of four approved systemic antifungal agents against 6,970 clinical isolates of Candida spp

The in vitro activities of ravuconazole and voriconazole were compared with those of amphotericin B, flucytosine (5FC), itraconazole, and fluconazole against 6,970 isolates of Candida spp. obtained from over 200 medical centers worldwide. Both ravuconazole and voriconazole were very active against all Candida spp. (MIC at which 90% of the isolates tested are inhibited [MIC(90)], 0.25 microg/ml; 98% of MICs were < or 1 microg/ml); however, a decrease in the activities of both of these agents was noted among isolates that were susceptible-dose dependent (fluconazole MIC, 16 to 32 microg/ml) and resistant (MIC, > or = 64 microg/ml) to fluconazole. Candida albicans was the most susceptible species (MIC(90) of both ravuconazole and voriconazole, 0.03 microg/ml), and C. glabrata was the least susceptible species (MIC(90), 1 to 2 microg/ml). Ravuconazole and voriconazole were each more active in vitro than amphotericin B, 5FC, itraconazole, and fluconazole against all Candida spp. and were the only agents with good in vitro activity against C. krusei. These results provide further evidence for the spectrum and potency of ravuconazole and voriconazole against a large and geographically diverse collection of Candida spp.     

In vitro susceptibilities of clinical yeast isolates to a new echinocandin derivative, LY303366, and other antifungal agents.

LY303366 is a new semisynthetic echinocandin derivative with potent, broad-spectrum fungicidal activity. We investigated the in vitro activity of LY303366, amphotericin B, flucytosine (5FC), fluconazole, and itraconazole against 435 clinical yeast isolates (413 Candida and 22 Saccharomyces cerevisiae isolates) obtained from over 30 different medical centers. MICs for all five antifungal agents were determined by the National Committee for Clinical Laboratory Standards method with RPMI 1640 test medium. LY303366 was also tested in antibiotic medium 3 as specified by the manufacturer. Overall, LY303366 was quite active against all of the yeast isolates when tested in RPMI 1640 (MIC at which 90% of the isolates are inhibited [MIC90], 1.0 microg/ml) but appeared to be considerably more potent when tested in antibiotic medium 3 (MIC90, 0.03 microg/ml). When tested in antibiotic medium 3, LY303366 was 16- to >2,000-fold more active than itraconazole, fluconazole, amphotericin B, or 5FC against all species except Candida parapsilosis. When tested in RPMI 1640, LY303366 was comparable to amphotericin B and itraconazole and more active than fluconazole and 5FC. All of the isolates for which fluconazole and itraconazole had elevated MICs (> or = 128 and > or = 2.0 microg/ml, respectively) were inhibited by < or = 0.007 microg of LY303366/ml when tested in antibiotic medium 3 and < or = 0.5 microg/ml when tested in RPMI 1640. Based on these studies, LY303366 has promising antifungal activity and warrants further in vitro and in vivo investigation.     

Comparison of the Etest and microdilution method for antifungal susceptibility testing of Cryptococcus neoformans to four antifungal agents

We performed a prospective study to compare the Etest and the microdilution method (NCCLS guidelines) for determining the MICs of fluconazole, itraconazole, flucytosine and amphotericin B for 35 strains of Cryptococcus neoformans. For the microdilution method (MDM) RPMI 1640 medium with 2% glucose was used for fluconazole, itraconazole and flucytosine, and Antibiotic Medium 3 for amphotericin B. For the Etest, RPMI 1640 medium with 2% glucose and solidified with 1.5% agar was used for the four antifungal agents. Amphotericin B was also tested on Antibiotic Medium 3 solidified with 1.5% agar. Fluconazole and flucytosine MICs by the Etest showed good correlation with the broth MDM (81.1 and 89.2% agreement within two dilutions, respectively). With the tested population of itraconazole- and amphotericin B-susceptible isolates, the MIC agreement for itraconazole was 54%; amphotericin B showed the lowest agreement (8.1% on Antibiotic Medium 3 and 13.5% on RPMI).     

The European Confederation of Medical Mycology (ECMM) survey of candidaemia in Italy: antifungal susceptibility patterns of 261 non-albicans Candida isolates from blood

OBJECTIVES: To analyse the in vitro antifungal susceptibility of 261 non-albicans Candida bloodstream strains isolated during the European Confederation of Medical Mycology survey of candidaemia performed in Lombardia, Italy (September 1997-December 1999). METHODS: In vitro susceptibility to flucytosine, fluconazole, itraconazole, posaconazole and voriconazole was determined using the broth microdilution method described in the NCCLS M27-A guidelines. Etest strips were used to assess susceptibility to amphotericin B. In vitro findings were correlated with the patient's underlying condition and previous antifungal treatment. RESULTS: MICs (mg/L) at which 90% of the strains were inhibited were, respectively, 2 for flucytosine, 8 for fluconazole, 0.5 for itraconazole, 0.25 for voriconazole and 0.25 for posaconazole. Amphotericin B MIC endpoints were <0.50 mg/L in all the isolates tested. Flucytosine resistance was detected in 19 isolates (7%), mainly among Candida tropicalis strains (30%). Innate or secondary fluconazole resistance was detected in 13 strains (5%). Among the 13 patients with fluconazole-resistant Candida bloodstream infection, three were HIV positive, including one treated with fluconazole for oral candidosis; the four who were HIV negative had received the azole during the 2 weeks preceding the candidaemia. Cross-resistance among fluconazole and other azoles was a rare event. CONCLUSIONS: Resistance is still uncommon in non-albicans Candida species recovered from blood cultures. However, in fungaemias caused by C. tropicalis, Candida glabrata and Candida krusei, there is a high prevalence of resistance to fluconazole and flucytosine. Fluconazole resistance should be suspected in patients treated previously with azoles, mainly those with advanced HIV infection.     

Rates of antifungal resistance among Spanish clinical isolates of Cryptococcus neoformans var. neoformans

OBJECTIVES: Activities in vitro of six antifungal agents were tested against a collection of 317 Cryptococcus neoformans var. neoformans clinical isolates. METHODS: The procedure described in document 7.1 by the European Committee on Antibiotic Susceptibility Testing with minor modifications was employed. RESULTS: Amphotericin B, itraconazole, voriconazole and ravuconazole exhibited a potent activity with geometric mean (GM) MICs under 0.26 mg/L. The GM MIC of flucytosine was 7.33 mg/L and that of fluconazole was 4.16 mg/L. The rates of antifungal resistance were 5.3% for amphotericin B, 0.9% for voriconazole and 3.1% for ravuconazole. Fifteen point eight per cent of strains had itraconazole MICs > or = 1 mg/L, and 46% of strains had flucytosine MICs > or = 8 mg/L. Fluconazole susceptibility (MIC < or = 8 mg/L) stood at 53.4%. CONCLUSIONS: The percentage of fluconazole susceptibility was significantly lower than that in other surveys. Cross-resistance to itraconazole was common (33.8%) but almost the whole collection was susceptible to voriconazole and ravuconazole. These results should be confirmed with prospective and population-based surveillance programmes.     

Antifungal susceptibility testing of isolates from a randomized, multicenter trial of fluconazole versus amphotericin B as treatment of nonneutropenic patients with candidemia. NIAID Mycoses Study Group and the Candidemia Study Group.

The antifungal susceptibilities of 232 pathogenic blood stream Candida isolates collected during a recently completed trial comparing fluconazole (400 mg/day) with amphotericin B (0.5 mg/kg of body weight per day) as treatment for candidemia in the nonneutropenic patient were determined both by the National committee for Clinical Laboratory Standards M27-P macrobroth methodology and by a less cumbersome broth microdilution methodology. For amphotericin B, M27-P yielded a very narrow range of MICs (0.125 to 1 microgram/ml) and there were no susceptibility differences among species. For fluconazole, a broad range of MICs were seen (0.125 to > 64 micrograms/ml), with characteristic MICs seen for each species in the rank order Candida albicans < C. parapsilosis approximately equal to C. lusitaniae < C. glabrata approximately equal to C. krusei approximately equal to C. lipolytica. The MIC distribution for C. tropicalis was bimodal and could not be ranked. Both microdilution MICs were within one tube dilution of the M27-P MIC for > 90% of isolates with amphotericin B and for > or = 77% of isolates with fluconazole. For both methods, elevated MICs did not predict treatment failure. In the case of amphotericin B, the MIC range was too narrow to permit identification of resistant isolates. In the case of fluconazole, MICs for isolates associated with failure to clear the bloodstream consistently were equivalent to the median MIC for the given species. Successful courses of therapy were seen with four isolates from four patients despite MICs of > or = 32 micrograms/ml. As MICs obtained by M27-P and similar methods correlate with responsiveness to fluconazole therapy in animal models and in AIDS patients with oropharyngeal candidiasis, the lack of correlation in this setting suggests that the MICs for these isolates are at or below the relevant fluconazole breakpoint for this dose of fluconazole and patient setting and that host factors such as failure to exchange intravenous catheters were more important than MIC in predicting outcome.     

Antifungal susceptibility testing of yeasts: evaluation of technical variables for test automation.

The technical parameters for antifungal susceptibility testing with Candida species were reexamined to determine the optimal conditions for testing with semiautomated preparations of broth microdilution cultures, automated spectrophotometric readings of the cultures, and dose-response and endpoint determinations by means of a computer spreadsheet. Tests were based on proposed standard method M27P of the National Committee for Clinical Laboratory Standards for antifungal agents. RPMI 1640 broth with extra glucose to a final concentration of 2% gave higher and more reproducible drug-free control readings without affecting susceptibility endpoint readings. An inoculum of 8 x 10(4) yeasts per ml prepared from a carbon-limiting broth culture without further standardization was found to give optimal control readings after 48 h of incubation at 37 degrees C. For flucytosine, fluconazole, itraconazole, and ketoconazole, endpoints based on 50% growth inhibition (50% inhibitory concentration) gave the minimum variation with inoculum size and the fewest endpoint differences with RPMI 1640 medium obtained from two different suppliers. The 50% inhibitory concentration was also the optimal endpoint for fluconazole and ketoconazole susceptibilities in comparison with broth macrodilution MICs determined by the method of the National Committee for Clinical Laboratory Standards. Intralaboratory reproducibility was determined by retrospective analysis of replicate results for isolates retested at random over a 2-year period. This approach showed less favorable reproducibility than has been reported from purpose-designed, prospective antifungal susceptibility studies, but it may better reflect real-life test reproducibility. Susceptibility data for 616 clinical isolates of yeasts, representing 16 Candida and Saccharomyces spp., confirmed the tendency of Candida lusitaniae isolates to show relatively low susceptibilities to amphotericin B, the tendency of Candida krusei isolates to show low flucytosine and fluconazole susceptibilities, and the presence of some isolates in the species Candida albicans, Candida glabrata, and Candida tropicalis with low susceptibilities to azole derivative antifungal agents. The study demonstrates the value of automation and standardization in all stages of yeast susceptibility testing, from plate preparation to data analysis.