Torulopsis glabrata: azole susceptibilities by microdilution colorimetric and macrodilution broth assays

Candida glabrata Fungemia: Experience in a Tertiary Care Center

BACKGROUND

During the past decade, Candida glabrata has emerged as an important cause of fungemia. We reviewed demographic data, risk factors, treatment, and outcomes associated with C. glabrata fungemia from 1995-2002 and performed susceptibility testing of isolates.

METHODS

Data on all episodes of fungemia were prospectively recorded, and the associated isolates were saved. Medical records were reviewed retrospectively. Susceptibility testing was performed for fluconazole, itraconazole, and voriconazole.

RESULTS

C. glabrata caused 103 (17%) of 609 fungemic episodes during the 8-year period that we studied. Medical records and isolates were available for 94 episodes that occurred in 91 patients. The patients included 42 men and 49 women. The mean age was 51 years. Thirty-four episodes (36%) occurred in patients >60 years old; only 3 episodes occurred in patients <1 year old. The most common predisposing factors were use of broad-spectrum antibiotics (in 86% of episodes), use of central venous catheters (77%), stay in an intensive care unit (48%), renal failure (46%), and receipt of parenteral nutrition (45%). Of the 94 episodes, 83 were treated with antifungal agents. The overall mortality rate at day 30 was 29%. For the 11 episodes that were not treated, the mortality rate was 64% (7 of 11 episodes). Outcome appeared to be unrelated to whether fluconazole or amphotericin B was administered. In vitro, 60% of isolates were resistant to fluconazole, 83% to itraconazole, and 44% to voriconazole. Susceptibility to these azoles did not change over the 8 years of the study.

CONCLUSION

C. glabrata fungemia was most often seen in older adults and was associated with a mortality rate of 29%. Outcomes appeared to be unrelated to in vitro susceptibility results and to the antifungal agent used.

In vitro susceptibility of yeasts for fluconazole and itraconazole. Evaluation of a microdilution test

In vitro susceptibilities were determined for a total of 159 clinical isolates and 12 reference strains of yeasts belonging to different Candida species including 94 Candida albicans strains, and further genera such as Cryptococcus, Trichosporon, Geotrichum and Saccharomyces. Minimum inhibitory concentration (MIC) values for fluconazole and itraconazole were assessed using a microdilution technique with the semisynthetic high resolution (HR) medium supplemented with glucose and asparagine but without sodium hydrogen carbonate (pH 7.0), according to a proposal of the working group 'Clinical Mycology' of the German Speaking Mycological Society. Fluconazole MIC values for C. albicans were between 0.125 and > or = 128 micrograms ml-1. Thus, the median of 1 microgram ml-1 showed that the overall fluconazole susceptibility was good. As expected, Candida krusei (seven strains) exhibited diminished in vitro susceptibility with MIC values for fluconazole of 8 to 128 micrograms ml-1 with a median of 64 micrograms ml-1. Some Candida kefyr strains seemed to be less susceptible against fluconazole which was indicated by a MIC90 of 64 micrograms ml-1. Surprisingly, no Candida glabrata isolate exhibited a MIC value greater than 16 micrograms ml-1. Other Candida species, Trichosporon cutaneum, Geotrichum candidum and Saccharomyces cerevisiae showed low MICs to fluconazole. In vitro susceptibility testing of itraconazole revealed that all Candida species except C. albicans, but also Trichosporon cutaneum, Geotrichum candidum, and Saccharomyces cerevisiae exhibited acceptable low MIC values against itraconazole (0.03-2 micrograms ml-1). Their MIC90 values for itraconazole were in the close range between 0.125 and 2 micrograms ml-1. MIC values between 0.125 and 2 micrograms ml-1 were obtained, even for C. krusei strains. On the other hand, the range of C. albicans MICs was between 0.0125 and > or = 16 micrograms ml-1 with MIC50 and MIC90 values of 0.125 and > or = 16 micrograms ml-1, respectively, indicating that a considerable number of yeast strains have high MICs. The comparative evaluation of different experimental conditions revealed that there exists a marked influence both of inoculum size and incubation time on the results of susceptibility testing. Therefore, for routine usage 10(2) CFU ml-1 and 18-24 h incubation time for this microdilution method with HR medium are recommended.

Colorimetric method for susceptibility testing of voriconazole and other triazoles against Candida species

A microdilution assay using Alamar Blue, a colorimetric indicator, was compared with the NCCLS macrodilution broth assay for voriconazole, fluconazole, and itraconazole against Candida albicans, Candida glabrata, and Candida krusei. Concordance (+/- 2 dilutions) between the two methods was highest for voriconazole (98.3%), and for fluconazole and itraconazole it was 94.3 and 95.4%, respectively. Twenty-six of 32 (81.2%) discordant readings (> or = 3 dilutions different) were noted in C. glabrata isolates, and all but two isolates showing discordance had higher minimum inhibitory concentration readings with the colorimetric method.

Detection of Candida dubliniensis in oropharyngeal samples from human immunodeficiency virus-infected patients in North America by primary CHROMagar candida screening and susceptibility testing of isolates

Candida dubliniensis has been associated with oropharyngeal candidiasis in patients infected with human immunodeficiency virus (HIV). C. dubliniensis isolates may have been improperly characterized as atypical Candida albicans due to the phenotypic similarity between the two species. Prospective screening of oral rinses from 63 HIV-infected patients detected atypical dark green isolates on CHROMagar Candida compared to typical C. albicans isolates, which are light green. Forty-eight atypical isolates and three control strains were characterized by germ tube formation, differential growth at 37, 42, and 45 degreesC, identification by API 20C, fluorescence, chlamydoconidium production, and fingerprinting by Ca3 probe DNA hybridization patterns. All isolates were germ tube positive. Very poor or no growth occurred at 42 degreesC with 22 of 51 isolates. All 22 poorly growing isolates at 42 degreesC and one isolate with growth at 42 degreesC showed weak hybridization of the Ca3 probe with genomic DNA, consistent with C. dubliniensis identification. No C. dubliniensis isolate but only 18 of 28 C. albicans isolates grew at 45 degreesC. Other phenotypic or morphologic tests were less reliable in differentiating C. dubliniensis from C. albicans. Antifungal susceptibility testing showed fluconazole MICs ranging from </=0.125 to 64 microgram/ml. Two isolates were resistant to fluconazole (MIC, 64 microgram/ml) and one strain was dose dependent susceptible (MIC, 16 microgram/ml). MICs of other azoles, including voriconazole, itraconazole, and SCH 56592, for these isolates were lower. C. dubliniensis was identified in 11 of 63 (17%) serially evaluated patients. Variability in phenotypic characteristics dictates the use of molecular and biochemical techniques to identify C. dubliniensis. This study identifies C. dubliniensis in HIV-infected patients from San Antonio, Tex., and shows that C. dubliniensis is frequently detected in those patients by using a primary CHROMagar screen.

Persistent oral candidosis by non-albicans Candida strains including Candida glabrata in a human immunodeficiency virus-infected patient observed over a period of 6 years

A 38-year-old woman infected with human immunodeficiency virus (HIV) presented with persistent oral candidosis in which non-albicans Candida strains were the predominant yeasts in most of the examinations performed over a period of 6 years. Oral treatment with fluconazole had no effect on clinical signs of oral candidosis. In 8 of a total of 11 specimens, Candida glabrata, Candida parapsilosis and Candida tropicalis were at least suspected as the causative pathogens of oral candidosis. The non-response to fluconazole in our patient could be explained by in vitro resistance to fluconazole of detected Candida glabrata and Candida tropicalis isolates.

In vitro activity of voriconazole against Candida species

The in vitro activity of voriconazole was compared with that of itraconazole and fluconazole against 181 isolates of Candida albicans, 124 isolates of Candida glabrata, and 20 isolates of Candida krusei obtained from the early 1980s through the mid-1990s. Voriconazole had greater intrinsic activity than fluconazole or itraconazole against all three Candida species. For C. glabrata, C. krusei, and C. albicans, the MIC50 values for voriconazole were 1 microgram/mL, 0.5 microgram/mL, and 0.01 microgram/mL, respectively compared with fluconazole MIC50 values of 8 micrograms/mL, 64 micrograms/mL, and 0.25 microgram/mL, respectively. If isolates from AIDS patients were excluded, MIC values for isolates from the 1990s were no higher than those noted for isolates from the 1980s. Voriconazole, a new triazole antifungal agent, appears to have enhanced activity against these three species of Candida; the clinical relevance of these findings should be studied in treatment trials.

Comparison of a photometric method with standardized methods of antifungal susceptibility testing of yeasts

We determined the fluconazole MICs for 101 clinical isolates of Candida and Cryptococcus neoformans using the macro- and microdilution methods recommended by the National Committee for Clinical Laboratory Standards. We compared the MICs obtained by these methods with those obtained by a photometric assay that quantified the reduction of 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) by viable fungi. The MIC determined by this method was defined as the highest fluconazole concentration associated with the first precipitous drop in optical density. For Candida, both the MTT and the microdilution methods demonstrated excellent agreement with the standard macrodilution method. The MTT method, however, generated MICs at 24 h that were comparable to those generated by the standard macrodilution method, whereas the microdilution method required 48 h. For C. neoformans, the levels of agreement between the MICs determined by the MTT and microdilution methods after 48 h and those determined by the standard 72-h macrodilution method were 94% (29 of 31) and 94% (29 of 31), respectively. The MTT method therefore provided results comparable to those of currently recommended methods and had the advantages of a more rapid turnaround time and potential adaptability to use as an automated system. Furthermore, the MICs determined by the MTT method were determined photometrically, thereby eliminating reader bias.

Multicenter randomized trial of fluconazole versus amphotericin B for treatment of candidemia in non-neutropenic patients. Canadian Candidemia Study Group

A randomized trial was conducted to compare the efficacy and safety of fluconazole versus that of amphotericin B in the treatment of candidemia in non-neutropenic adults. Enrollment was stratified by disease severity (APACHE II score). Patients were randomized (1:1) to receive amphotericin B 0.6 mg/kg/day (cumulative dose 8 mg/kg) or fluconazole 800 mg intravenous loading dose, then 400 mg daily for four weeks (intravenous for at least 10 days). Patients were monitored for six months. A total of 106 patients were enrolled. A protocol amendment implemented midway through the trial required patients to be removed from the study and treated with amphotericin B if species identification indicated candidemia due to Candida glabrata or Candida krusei. Baseline characteristics were similar for the two groups; 103 patients (fluconazole, 50; amphotericin B, 53) met the major enrollment criteria. The intention-to-treat analysis indicated successful therapy in 50% of fluconazole recipients compared to 58% of the amphotericin B group (p = 0.39; one-sided 95% CI, -8 to 24%). The efficacy analysis included 84 patients (fluconazole, 42; amphotericin B, 42); successful outcomes were observed in 57% and 62% of cases in the fluconazole and amphotericin B groups, respectively (p = 0.66: one-sided 95% CI, -12 to 22%). The mortality at day 14 for the fluconazole group was 26% and for the amphotericin B group 21% (p = 0.52; chi-square test) and remained similar throughout the course of follow-up, Drug-related adverse events were more frequent with amphotericin B than with fluconazole and prompted switching of therapy for two (4%) and zero cases, respectively. Fluconazole and amphotericin B were associated with similar clinical response rates and survival in the treatment of candidemia among non-neutropenic patients; however, drug-related adverse events were more frequent with amphotericin B.

Antifungal agents in the 1990s. Current status and future developments

Significant advances in antifungal therapy have occurred in the last decade. Most of these advances have been tied to the introduction of the triazoles, itraconazole and fluconazole. Itraconazole has proved efficacious for the treatment of subacute to chronic infections with the endemic mycoses and other opportunistic filamentous fungi, including Aspergillus spp. Fluconazole is now routinely used for mucocutaneous and systemic candidiasis, and its use for coccidioidal meningitis has obviated the need for intrathecal amphotericin B in most patients. Large, well controlled trials in AIDS patients with cryptococcal meningitis have shown the benefit of induction therapy with amphotericin B and flucytosine, followed by consolidation and life-long maintenance therapy with fluconazole. Concomitant with the increased use of these well tolerated, effective oral triazole agents has come the emergence of drug resistance in AIDS patients and shifts in the species of yeasts causing infection in hospitalised patients. Amphotericin B remains the drug of choice for many fungal infections, especially those that are life-threatening. Lipid-containing formulations of amphotericin B have recently been approved: these preparations significantly reduce the risk of amphotericin B-induced nephrotoxicity. Several new fungicidal agents are currently in early trials. With the increasing number of available antifungal drugs, future studies will help define the appropriate niche for each and the possible benefit of therapy with combinations of drugs.

Comparison of rapid testing methods for enzyme production with the germ tube method for presumptive identification of Candida albicans

The observation of germ tube production as a method for the presumptive identification of Candida albicans has been in use for many years. Methods have recently been developed for detecting the production of the enzymes L-proline aminopeptidase and beta-galactosaminidase by yeast isolates grown in culture. Both enzymes are produced by C. albicans; other yeasts may produce either L-proline aminopeptidase or beta-galactosaminidase but not both enzymes. One hundred thirty-three clinical yeast isolates, including 55 C. albicans, 27 Candida tropicalis, 22 Torulopsis (Candida) glabrata, and 29 other yeast isolates were tested by the germ tube production method and three tests for enzyme production, with the API 20C method used as a "gold standard." All three enzymatic methods evaluated provided more objective and rapid nonmicroscopic alternatives to the germ tube test and may be used to accurately distinguish C. albicans from other yeasts.

[In vitro susceptibility testing of Candida species against fluconazole using the microdilution test with Alamar Blue]

The investigation of susceptibility of Candida species to fluconazole was performed in microdilution to a supplemented HR-medium. The sufficient reproducibility of the test was verified using special control isolates and isolates of patients. The excellent applicability of the method in routine diagnostics was evaluated by in vitro testing of susceptibility of 279 Candida isolates from patients being colonised or suffering from endomycoses. The Candida species showed different susceptibility against fluconazole: 96% of the C. albicans isolates were sensitive, 55% of the C. glabrata isolates had a reduced sensitivity, and 26% were resistant against fluconazole (MIC > 25 micrograms/ml). C. krusei isolates were highly resistant (9 of 11 strains).

Saccharomyces cerevisiae infections and antifungal susceptibility studies by colorimetric and broth macrodilution methods

Saccharomyces cerevisiae was isolated in large numbers from operative specimens from two patients with perforated bowel and peritonitis and from the blood of another patient treated with extracorporeal membrane oxygenation. Susceptibility studies were performed on these three isolates and another 29 isolates that colonized or caused infection in a total of 19 patients seen over the last decade. All isolates had low minimum inhibitory concentration (MIC) values for amphotericin B (MIC90 of < or = 0.02 microgram/ml) and flucytosine (MIC90 of 0.2 microgram/ml), and a broader range of MIC values for itraconazole (MIC90 of 0.8 microgram/ml) and fluconazole (MIC90 of 4 micrograms/ml). A colorimetric method using Alamar blue reagent showed good concordance with the standard broth macrodilution method for amphotericin B, flucytosine, and fluconazole, but less good concordance for itraconazole. Serious infections with S. cerevisiae probably should be treated with amphotericin B, with or without the addition of flucytosine.