Activities of Available and Investigational Antifu
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微生物临床杂志 2005年第1期
Departments of Internal Medicine
Pathology, Roy J. and Lucille A. Carver College of Medicine
Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, Iowa
ABSTRACT
Rhodotorula species are emerging pathogens in immunocompromised patients. We report the in vitro activities of eight antifungals against 64 Rhodotorula isolates collected in surveillance programs between 1987 and 2003. Rhodotorula strains are resistant in vitro to fluconazole (MIC at which 50% of the isolates tested are inhibited [MIC50], >128 μg/ml) and caspofungin (MIC50, >8 μg/ml). Amphotericin B (MIC50,1 μg/ml) and flucytosine (MIC50, 0.12 μg/ml) are both active in vitro, and the new and investigational triazoles all have some in vitro activity, with ravuconazole being the most active (MIC50, 0.25 μg/ml).
TEXT
Rhodotorula species, yeasts that belong to the family Cryptococcaceae, have been increasingly recognized as important human pathogens (1, 4, 7, 8, 10-12, 14, 18, 21, 23). Immunocompromised patients, particularly those with central venous catheters or other indwelling devices, are at highest risk for infection (10, 14, 18). While Rhodotorula strains appear to be less virulent than the more common yeast pathogens such as Candida and Cryptococcus neoformans, Rhodotorula infection has been associated with a crude mortality of up to 15% (12) and can cause sepsis syndrome and other life-threatening complications (4, 10, 13). Rhodotorula bloodstream infections have been successfully managed with line removal alone, antifungal therapy without line removal, and with a combination of these approaches (7, 10). Regarding choice of antifungal therapy, previously reported data have shown amphotericin B and flucytosine (5-FC) to have good in vitro activities and fluconazole and the echinocandins to have poor in vitro activities (2, 5, 6, 20, 23). However, most reports describe fewer than 10 organisms, not all utilize standard NCCLS methodology, and only a few report data on the newer extended-spectrum triazoles (2, 5, 6, 23).
For these reasons, we decided to examine the in vitro activities of agents against over 60 Rhodotorula isolates we have collected as part of antifungal resistance surveillance surveys since the late 1980s, utilizing standardized NCCLS methods and including new and investigational antifungal agents. To our knowledge, this represents the largest collection of clinical Rhodotorula isolates for which susceptibility test results obtained by standard NCCLS methods have been reported.
Sixty-four isolates of Rhodotorula were collected between 1987 and 2003 as part of several antifungal surveillance surveys (19). Sixty (94%) were human clinical isolates, the majority (n = 36 [56%]) from bloodstream (n = 28) or other sterile sites (n = 8). All isolates were stored as suspensions in sterile distilled water at room temperature until used in the study. Prior to testing, each isolate was subcultured at least twice on potato dextrose agar plates (Remel, Lenexa, Kans.) to ensure purity and optimal growth. We confirmed species identification by using the Vitek and API yeast identification systems (bioMerieux, Inc., Hazelwood, Mo.) supplemented by conventional methods as needed (9). Voriconazole (Pfizer), fluconazole (Pfizer), itraconazole (Janssen), ravuconazole (Bristol-Myers Squibb), posaconazole (Schering), and caspofungin (Merck) were obtained from their respective manufacturers, and 5-FC and amphotericin B were obtained from Sigma (St. Louis, Mo.). Stock solutions were prepared in dimethyl sulfoxide, polyethylene glycol (itraconazole), or water (5-FC) and further diluted in RPMI 1640 medium buffered to pH 7.0 with 0.165 M morpholinepropanesulfonic acid (MOPS) buffer (Sigma) and were dispensed into 96-well microdilution trays. Trays containing a 0.1-ml aliquot of the appropriate drug solution (two times the final concentration) in each well were subjected to quality control (QC) testing and then sealed and stored at –70°C until used in the study. Fluconazole and 5-FC concentrations in the wells ranged from 0.12 to 128 μg/ml and 0.06 to 64 μg/ml, respectively, while concentrations of all other agents ranged from 0.007 to 8 μg/ml.
Susceptibility testing was performed by the broth microdilution method according to the recommendations of NCCLS document M27-A2 (16). An inoculum suspension to match the turbidity of a 0.5 McFarland standard, diluted to a concentration of 1.0 x 103 to 5.0 x 103 cells per ml, was standardized spectrophotometrically, and an aliquot of 0.1 ml was added to each well of the microdilution tray (final inoculum, 0.5 x 103 to 2.5 x 103 cells/ml). In each case, the inoculum size was verified by colony counting. The microdilution trays were incubated at 35°C. However, two isolates were also incubated at 30°C because growth at 35°C was insufficient for endpoint determination. The MIC endpoints were read visually following 72 h of incubation. The MIC of amphotericin B was defined as the lowest concentration that produced complete inhibition of growth (first clear well). The MICs of all other tested agents were defined as the lowest concentration that produced a prominent decrease in turbidity compared to the drug-free control well.
Because broth dilution testing of amphotericin B may not be sensitive enough to detect some antifungal-resistant yeasts (e.g., Candida) (22), we also tested this agent by the Etest method as we have previously described for testing amphotericin B against C. neoformans (15).
QC testing was performed in accordance with NCCLS document M27-A2 and limits established by Barry et al. (3), using Candida krusei ATCC 6258 and Candida parapsilosis ATCC 22019 (16).
Of the 64 Rhodotorula isolates examined, 29 were R. glutinis, 24 were R. mucilaginosa, 5 were R. minuta, and 6 were not identified to the species level. The results of susceptibility testing overall and by the two major species are outlined in Table 1.
Amphotericin B MICs by broth dilution clustered around a value of 1 μg/ml, but Etest demonstrated a wider range of MICs and detected eight isolates for which the MIC was >1 μg/ml, raising the possibility that some Rhodotorula isolates may be less susceptible in vitro or in vivo than prior data would suggest.
5-FC was the most active in vitro of all the agents tested, with all isolates inhibited at 0.5 μg/ml. This agent has been used in treatment of serious Rhodotorula infections (4, 17), and it should be considered a first-line agent in combination with amphotericin B for invasive Rhodotorula infections.
Our data confirm that the echinocandin caspofungin does not have in vitro activity against Rhodotorula, as would be expected given the lack of activity of echinocandins against other members of the family Cryptococcaceae (6).
Our collection of Rhodotorula isolates is large enough to highlight the differences in potency within the azole antifungal class. As has been previously described, fluconazole is not active in vitro, and the MIC of itraconazole for almost 30% of isolates is >4 μg/ml. The newer broad-spectrum azoles are more active, with MICs at which 90% of the isolates tested are inhibited (MIC90s) of 4 μg/ml. Interestingly, of the broad-spectrum azoles tested, ravuconazole MICs were about fourfold lower than voriconazole or posaconazole MICs (MIC50/MIC90, 0.25/1 versus 2/4).
We noted no significant differences in the activities of any of the tested agents according to the species of Rhodotorula.
In summary, our results confirm previous reports of the in vitro activities of amphotericin B and 5-FC against Rhodotorula, as well as the absence of activity of the commonly used agents fluconazole and caspofungin. Each of the newer triazoles has some activity and may be useful as an alternative agent, but additional clinical experience is needed. Ravuconazole in particular showed excellent in vitro activity, and if this agent were further developed for clinical use, it might have a role in treatment of life-threatening or refractory Rhodotorula infections.
REFERENCES
Alliot, C., B. Desablens, R. Garidi, and S. Tabuteau. 2000. Opportunistic infection with Rhodotorula in cancer patients treated by chemotherapy: two case reports. Clin. Oncol. 12:115-117.
Barchiesi, F., D. Arzeni, A. W. Fothergill, L. F. Di Francesco, F. Caselli, M. G. Rinaldi, and G. Scalise. 2000. In vitro activities of the new antifungal triazole SCH 56592 against common and emerging yeast pathogens. Antimicrob. Agents Chemother. 44:226-229.
Barry, A. L., M. A. Pfaller, S. D. Brown, A. Espinel-Ingroff, M. A. Ghannoum, C. Knapp, R. P. Rennie, J. H. Rex, and M. G. Rinaldi. 2000. Quality control limits for broth microdilution susceptibility tests of ten antifungal agents. J. Clin. Microbiol. 38:3457-3459.
Braun, D. K., and C. A. Kaufmann. 1999. Rhodotorula fungemia: a life-threatening complication of indwelling central venous catheters. Mycoses 35:305-308.
Espinel-Ingroff, A. 1998. In vitro activity of the new triazole voriconazole (UK-109,496) against opportunistic filamentous and dimorphic fungi and common and emerging yeast pathogens. J. Clin. Microbiol. 36:198-202.
Espinel-Ingroff, A. 1998. Comparison of in vitro activities of the new triazole SCH56592 and the echinocandins MK-0991 (L-743,872) and LY303366 against opportunistic filamentous and dimorphic fungi and yeasts. J. Clin. Microbiol. 36:2950-2956.
Goldani, L. Z., D. E. Craven, and A. M. Sugar. 1995. Central venous catheter infection with Rhodotorula minuta in a patient with AIDS taking suppressive doses of fluconazole. J. Med. Vet. Mycol. 33:267-270.
Hazen, K. C. 1995. New and emerging yeast pathogens. Clin. Microbiol. Rev. 8:462-478.
Hazen, K. C., and S. A. Howell. 2003. Candida, Cryptococcus, and other yeasts of medical importance, p. 1693-1711. In P. R. Murray, E. J. Baron, J. H. Jorgensen, M. A. Pfaller, and R. H. Yolken (ed.), Manual of clinical microbiology, 8th ed. ASM Press, Washington, D.C.
Kiehn, T. E., E. Gorey, A. E. Brown, F. F. Edwards, and D. Armstrong. 1992. Sepsis due to Rhodotorula related to use of indwelling central venous catheters. Clin. Infect. Dis. 14:841-846.
Kiraz, N., Z. Gulbas, and Y. Agkun. 2000. Case report: Rhodotorula rubra fungemia due to use of indwelling venous catheters. Mycoses 43:209-210.
Krcmery, V., I. Krupova, and D. W. Denning. 1999. Invasive yeast infections other than Candida spp. in acute leukaemia. J. Hosp. Infect. 41:181-194.
Leeber, D. A., and I. Scher. 1969. Rhodotorula fungemia presenting as ‘endotoxic’ shock. Arch. Intern. Med. 123:78-81.
Lo Re, V., III, N. O. Fishman, and I. Nachamkin. 2003. Recurrent catheter-related Rhodotorula rubra infection. Clin. Microbiol. Infect. 9:897-900.
Maxwell, M. J., S. A. Messer, R. J. Hollis, D. J. Diekema, and M. A. Pfaller. 2003. Evaluation of Etest method for determining voriconazole and amphotericin B MICs for 162 clinical isolates of Cryptococcus neoformans. J. Clin. Microbiol. 41:97-99.
National Committee for Clinical Laboratory Standards. 2002. Reference method for broth dilution antifungal susceptibility testing of yeasts: approved standard, 2nd ed. NCCLS document M27-A2. NCCLS, Wayne, Pa.
Naveh, Y., A. Friedman, D. Merzbach, and N. Hashman. 1975. Endocarditis caused by Rhodotorula successfully treated with 5-flucytosine. Br. Heart J. 37:100-104.
Petrocheilou-Paschou, V., H. Prifti, E. Kostis, C. Papadimitriou, M. A. Dimopoulos, and S. Stamatelopoulos. 2001. Rhodotorula septicemia: case report and minireview. Clin. Microbiol. Infect. 7:100-102.
Pfaller, M. A., and D. J. Diekema. 2002 The role of sentinel surveillance of candidemia: trends in species distribution and antifungal susceptibility. J. Clin. Microbiol. 40:3551-3557.
Preney, L., M. Theraud, C. Guiguen, and J. P. Gangneux. 2003. Experimental evaluation of antifungal and antiseptic agents against Rhodotorula spp. Mycoses 46:492-495.
Samonis, G., M. Anatolotaki, H. Apostolakou, S. Maraki, D. Mavroudis, and V. Georgoulas. 2001. Transient fungemia due to Rhodotorula rubra in a cancer patient: case report and review of the literature. Infection 29:173-176.
Wanger, A., K. Mills, P. W. Nelson, and J. H. Rex. 1995. Comparison of Etest and National Committee for Clinical Laboratory Standards broth macrodilution method for antifungal susceptibility testing: enhanced ability to detect amphotericin B-resistant Candida isolates. Antimicrob. Agents Chemother. 39:2520-2522.
Zaas, A. K., M. Boyce, W. Schell, B. Alexander Lodge, J. L. Miller, and J. R. Perfect. 2003. Risk of fungemia due to Rhodotorula and antifungal susceptibility testing of Rhodotorula isolates. J. Clin. Microbiol. 41:5233-5235.(D. J. Diekema, B. Petroel)
Pathology, Roy J. and Lucille A. Carver College of Medicine
Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, Iowa
ABSTRACT
Rhodotorula species are emerging pathogens in immunocompromised patients. We report the in vitro activities of eight antifungals against 64 Rhodotorula isolates collected in surveillance programs between 1987 and 2003. Rhodotorula strains are resistant in vitro to fluconazole (MIC at which 50% of the isolates tested are inhibited [MIC50], >128 μg/ml) and caspofungin (MIC50, >8 μg/ml). Amphotericin B (MIC50,1 μg/ml) and flucytosine (MIC50, 0.12 μg/ml) are both active in vitro, and the new and investigational triazoles all have some in vitro activity, with ravuconazole being the most active (MIC50, 0.25 μg/ml).
TEXT
Rhodotorula species, yeasts that belong to the family Cryptococcaceae, have been increasingly recognized as important human pathogens (1, 4, 7, 8, 10-12, 14, 18, 21, 23). Immunocompromised patients, particularly those with central venous catheters or other indwelling devices, are at highest risk for infection (10, 14, 18). While Rhodotorula strains appear to be less virulent than the more common yeast pathogens such as Candida and Cryptococcus neoformans, Rhodotorula infection has been associated with a crude mortality of up to 15% (12) and can cause sepsis syndrome and other life-threatening complications (4, 10, 13). Rhodotorula bloodstream infections have been successfully managed with line removal alone, antifungal therapy without line removal, and with a combination of these approaches (7, 10). Regarding choice of antifungal therapy, previously reported data have shown amphotericin B and flucytosine (5-FC) to have good in vitro activities and fluconazole and the echinocandins to have poor in vitro activities (2, 5, 6, 20, 23). However, most reports describe fewer than 10 organisms, not all utilize standard NCCLS methodology, and only a few report data on the newer extended-spectrum triazoles (2, 5, 6, 23).
For these reasons, we decided to examine the in vitro activities of agents against over 60 Rhodotorula isolates we have collected as part of antifungal resistance surveillance surveys since the late 1980s, utilizing standardized NCCLS methods and including new and investigational antifungal agents. To our knowledge, this represents the largest collection of clinical Rhodotorula isolates for which susceptibility test results obtained by standard NCCLS methods have been reported.
Sixty-four isolates of Rhodotorula were collected between 1987 and 2003 as part of several antifungal surveillance surveys (19). Sixty (94%) were human clinical isolates, the majority (n = 36 [56%]) from bloodstream (n = 28) or other sterile sites (n = 8). All isolates were stored as suspensions in sterile distilled water at room temperature until used in the study. Prior to testing, each isolate was subcultured at least twice on potato dextrose agar plates (Remel, Lenexa, Kans.) to ensure purity and optimal growth. We confirmed species identification by using the Vitek and API yeast identification systems (bioMerieux, Inc., Hazelwood, Mo.) supplemented by conventional methods as needed (9). Voriconazole (Pfizer), fluconazole (Pfizer), itraconazole (Janssen), ravuconazole (Bristol-Myers Squibb), posaconazole (Schering), and caspofungin (Merck) were obtained from their respective manufacturers, and 5-FC and amphotericin B were obtained from Sigma (St. Louis, Mo.). Stock solutions were prepared in dimethyl sulfoxide, polyethylene glycol (itraconazole), or water (5-FC) and further diluted in RPMI 1640 medium buffered to pH 7.0 with 0.165 M morpholinepropanesulfonic acid (MOPS) buffer (Sigma) and were dispensed into 96-well microdilution trays. Trays containing a 0.1-ml aliquot of the appropriate drug solution (two times the final concentration) in each well were subjected to quality control (QC) testing and then sealed and stored at –70°C until used in the study. Fluconazole and 5-FC concentrations in the wells ranged from 0.12 to 128 μg/ml and 0.06 to 64 μg/ml, respectively, while concentrations of all other agents ranged from 0.007 to 8 μg/ml.
Susceptibility testing was performed by the broth microdilution method according to the recommendations of NCCLS document M27-A2 (16). An inoculum suspension to match the turbidity of a 0.5 McFarland standard, diluted to a concentration of 1.0 x 103 to 5.0 x 103 cells per ml, was standardized spectrophotometrically, and an aliquot of 0.1 ml was added to each well of the microdilution tray (final inoculum, 0.5 x 103 to 2.5 x 103 cells/ml). In each case, the inoculum size was verified by colony counting. The microdilution trays were incubated at 35°C. However, two isolates were also incubated at 30°C because growth at 35°C was insufficient for endpoint determination. The MIC endpoints were read visually following 72 h of incubation. The MIC of amphotericin B was defined as the lowest concentration that produced complete inhibition of growth (first clear well). The MICs of all other tested agents were defined as the lowest concentration that produced a prominent decrease in turbidity compared to the drug-free control well.
Because broth dilution testing of amphotericin B may not be sensitive enough to detect some antifungal-resistant yeasts (e.g., Candida) (22), we also tested this agent by the Etest method as we have previously described for testing amphotericin B against C. neoformans (15).
QC testing was performed in accordance with NCCLS document M27-A2 and limits established by Barry et al. (3), using Candida krusei ATCC 6258 and Candida parapsilosis ATCC 22019 (16).
Of the 64 Rhodotorula isolates examined, 29 were R. glutinis, 24 were R. mucilaginosa, 5 were R. minuta, and 6 were not identified to the species level. The results of susceptibility testing overall and by the two major species are outlined in Table 1.
Amphotericin B MICs by broth dilution clustered around a value of 1 μg/ml, but Etest demonstrated a wider range of MICs and detected eight isolates for which the MIC was >1 μg/ml, raising the possibility that some Rhodotorula isolates may be less susceptible in vitro or in vivo than prior data would suggest.
5-FC was the most active in vitro of all the agents tested, with all isolates inhibited at 0.5 μg/ml. This agent has been used in treatment of serious Rhodotorula infections (4, 17), and it should be considered a first-line agent in combination with amphotericin B for invasive Rhodotorula infections.
Our data confirm that the echinocandin caspofungin does not have in vitro activity against Rhodotorula, as would be expected given the lack of activity of echinocandins against other members of the family Cryptococcaceae (6).
Our collection of Rhodotorula isolates is large enough to highlight the differences in potency within the azole antifungal class. As has been previously described, fluconazole is not active in vitro, and the MIC of itraconazole for almost 30% of isolates is >4 μg/ml. The newer broad-spectrum azoles are more active, with MICs at which 90% of the isolates tested are inhibited (MIC90s) of 4 μg/ml. Interestingly, of the broad-spectrum azoles tested, ravuconazole MICs were about fourfold lower than voriconazole or posaconazole MICs (MIC50/MIC90, 0.25/1 versus 2/4).
We noted no significant differences in the activities of any of the tested agents according to the species of Rhodotorula.
In summary, our results confirm previous reports of the in vitro activities of amphotericin B and 5-FC against Rhodotorula, as well as the absence of activity of the commonly used agents fluconazole and caspofungin. Each of the newer triazoles has some activity and may be useful as an alternative agent, but additional clinical experience is needed. Ravuconazole in particular showed excellent in vitro activity, and if this agent were further developed for clinical use, it might have a role in treatment of life-threatening or refractory Rhodotorula infections.
REFERENCES
Alliot, C., B. Desablens, R. Garidi, and S. Tabuteau. 2000. Opportunistic infection with Rhodotorula in cancer patients treated by chemotherapy: two case reports. Clin. Oncol. 12:115-117.
Barchiesi, F., D. Arzeni, A. W. Fothergill, L. F. Di Francesco, F. Caselli, M. G. Rinaldi, and G. Scalise. 2000. In vitro activities of the new antifungal triazole SCH 56592 against common and emerging yeast pathogens. Antimicrob. Agents Chemother. 44:226-229.
Barry, A. L., M. A. Pfaller, S. D. Brown, A. Espinel-Ingroff, M. A. Ghannoum, C. Knapp, R. P. Rennie, J. H. Rex, and M. G. Rinaldi. 2000. Quality control limits for broth microdilution susceptibility tests of ten antifungal agents. J. Clin. Microbiol. 38:3457-3459.
Braun, D. K., and C. A. Kaufmann. 1999. Rhodotorula fungemia: a life-threatening complication of indwelling central venous catheters. Mycoses 35:305-308.
Espinel-Ingroff, A. 1998. In vitro activity of the new triazole voriconazole (UK-109,496) against opportunistic filamentous and dimorphic fungi and common and emerging yeast pathogens. J. Clin. Microbiol. 36:198-202.
Espinel-Ingroff, A. 1998. Comparison of in vitro activities of the new triazole SCH56592 and the echinocandins MK-0991 (L-743,872) and LY303366 against opportunistic filamentous and dimorphic fungi and yeasts. J. Clin. Microbiol. 36:2950-2956.
Goldani, L. Z., D. E. Craven, and A. M. Sugar. 1995. Central venous catheter infection with Rhodotorula minuta in a patient with AIDS taking suppressive doses of fluconazole. J. Med. Vet. Mycol. 33:267-270.
Hazen, K. C. 1995. New and emerging yeast pathogens. Clin. Microbiol. Rev. 8:462-478.
Hazen, K. C., and S. A. Howell. 2003. Candida, Cryptococcus, and other yeasts of medical importance, p. 1693-1711. In P. R. Murray, E. J. Baron, J. H. Jorgensen, M. A. Pfaller, and R. H. Yolken (ed.), Manual of clinical microbiology, 8th ed. ASM Press, Washington, D.C.
Kiehn, T. E., E. Gorey, A. E. Brown, F. F. Edwards, and D. Armstrong. 1992. Sepsis due to Rhodotorula related to use of indwelling central venous catheters. Clin. Infect. Dis. 14:841-846.
Kiraz, N., Z. Gulbas, and Y. Agkun. 2000. Case report: Rhodotorula rubra fungemia due to use of indwelling venous catheters. Mycoses 43:209-210.
Krcmery, V., I. Krupova, and D. W. Denning. 1999. Invasive yeast infections other than Candida spp. in acute leukaemia. J. Hosp. Infect. 41:181-194.
Leeber, D. A., and I. Scher. 1969. Rhodotorula fungemia presenting as ‘endotoxic’ shock. Arch. Intern. Med. 123:78-81.
Lo Re, V., III, N. O. Fishman, and I. Nachamkin. 2003. Recurrent catheter-related Rhodotorula rubra infection. Clin. Microbiol. Infect. 9:897-900.
Maxwell, M. J., S. A. Messer, R. J. Hollis, D. J. Diekema, and M. A. Pfaller. 2003. Evaluation of Etest method for determining voriconazole and amphotericin B MICs for 162 clinical isolates of Cryptococcus neoformans. J. Clin. Microbiol. 41:97-99.
National Committee for Clinical Laboratory Standards. 2002. Reference method for broth dilution antifungal susceptibility testing of yeasts: approved standard, 2nd ed. NCCLS document M27-A2. NCCLS, Wayne, Pa.
Naveh, Y., A. Friedman, D. Merzbach, and N. Hashman. 1975. Endocarditis caused by Rhodotorula successfully treated with 5-flucytosine. Br. Heart J. 37:100-104.
Petrocheilou-Paschou, V., H. Prifti, E. Kostis, C. Papadimitriou, M. A. Dimopoulos, and S. Stamatelopoulos. 2001. Rhodotorula septicemia: case report and minireview. Clin. Microbiol. Infect. 7:100-102.
Pfaller, M. A., and D. J. Diekema. 2002 The role of sentinel surveillance of candidemia: trends in species distribution and antifungal susceptibility. J. Clin. Microbiol. 40:3551-3557.
Preney, L., M. Theraud, C. Guiguen, and J. P. Gangneux. 2003. Experimental evaluation of antifungal and antiseptic agents against Rhodotorula spp. Mycoses 46:492-495.
Samonis, G., M. Anatolotaki, H. Apostolakou, S. Maraki, D. Mavroudis, and V. Georgoulas. 2001. Transient fungemia due to Rhodotorula rubra in a cancer patient: case report and review of the literature. Infection 29:173-176.
Wanger, A., K. Mills, P. W. Nelson, and J. H. Rex. 1995. Comparison of Etest and National Committee for Clinical Laboratory Standards broth macrodilution method for antifungal susceptibility testing: enhanced ability to detect amphotericin B-resistant Candida isolates. Antimicrob. Agents Chemother. 39:2520-2522.
Zaas, A. K., M. Boyce, W. Schell, B. Alexander Lodge, J. L. Miller, and J. R. Perfect. 2003. Risk of fungemia due to Rhodotorula and antifungal susceptibility testing of Rhodotorula isolates. J. Clin. Microbiol. 41:5233-5235.(D. J. Diekema, B. Petroel)