1 Istituto di Malattie Infettive e Medicina Pubblica, Università degli Studi di Ancona, Azienda Ospedaliera Umberto I°, Via Conca 60020, Torrette di Ancona, Ancona; 2 Dipartimento di Medicina Interna e Medicina Pubblica, Sezione Igiene, Università degli Studi di Bari, Italy
Received 29 July 2002; returned 6 October 2002; revised 31 October 2002; accepted 4 November 2002
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Abstract |
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Keywords: antifungal susceptibility, yeast isolates
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Introduction |
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In this study, we analysed the antifungal susceptibility profiles of yeast isolates causing bloodstream infections in patients hospitalized between January 1998 and June 2001 at the University Hospital of Bari, Italy. The antifungal activities of three triazoles (fluconazole, itraconazole and posaconazole), 5-fluorocytosine and amphotericin B were investigated.
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Materials and methods |
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A total of 83 clinical yeast isolates were used in this study. The strains were isolated from the blood of 59 patients hospitalized in six departments of the University Hospital of Bari, Italy, from January 1998 to June 2001. The departments included: the Intensive Care Unit [number of patients (n) = 19], Oncology Paediatric Unit (n = 16), Surgery (n = 11), Neonatology (n = 8), Transplant Unit (n = 3) and Haematology (n = 2). Sixty of 83 isolates represented the first isolation strain (one patient had a mixed fungaemia). They included: 28 strains of Candida albicans, 23 strains of Candida parapsilosis, three strains of Candida tropicalis, two strains each of Candida glabrata and Trichosporon capitatum and one strain each of Saccharomyces cerevisiae and Hansenula anomala. There were 23 patients for whom fungaemia, sustained by the same yeast species of the first isolation, persisted despite antifungal therapy. Therefore, an additional 23 isolates (11 C. albicans, 10 C. parapsilosis, one C. tropicalis and one T. capitatum) were available for antifungal susceptibility testing. Intervals between the first and last isolation ranged from 6 to 27 days. Yeast isolates were identified at the species level by conventional morphological and biochemical methods, and were stored at room temperature. Before the initiation of the study, yeast isolates were subcultured on antimicrobial agent-free medium to ensure viability and purity. C. albicans ATCC 90029 and Candida krusei ATCC 6258 were used as quality controls and tested in each run of the experiments.2,3
Antifungal agents
Standard powders of fluconazole (Pfizer, Inc., New York, NY, USA), itraconazole (Janssen, Beerse, Belgium) and posaconazole (Schering-Plough Research Institute, Kenilworth, NJ, USA) were obtained from their respective manufacturers. 5-Fluorocytosine and amphotericin B were purchased from Sigma (Milan, Italy). Serial two-fold dilutions were prepared as recommended by the NCCLS.3 Final dilutions were made in RPMI 1640 medium (Sigma) buffered to pH 7.0 with 0.165 M MOPS buffer (Sigma). Following incubation at 35°C for 48 h, the MICs of triazoles and 5-fluorocytosine were determined as the lowest concentration at which a prominent decrease in turbidity relative to the growth control well was observed. Amphotericin B MIC was determined as the lowest concentration at which no growth was detectable.3
Definitions
Interpretative criteria for susceptibility to fluconazole, itraconazole and 5-fluorocytosine were those published by Rex et al.4 and by the NCCLS.3 According to that previously reported by Nguyen et al.5 and Pfaller et al.,1 we selected a breakpoint of >1.0 mg/L to define isolates as amphotericin B resistant. Owing to preliminary pharmacokinetic data, and according to that reported by Pfaller et al.,1 we selected a breakpoint of 1 mg/L to define isolates as posaconazole resistant.
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Results and discussion |
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In conclusion, we confirmed that up to 95% of yeast isolates causing bloodstream infections are susceptible in vitro to antifungal agents. Clearly, prospective MIC-directed clinical trials are warranted to further elucidate the potential predictive utility of antifungal susceptibility testing in this setting.
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Acknowledgements |
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Footnotes |
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References |
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2
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Barry, A. L., Pfaller, M. A., Brown, S. D., Espinel-Ingroff, A., Ghannoum, M. A., Knapp, C. et al. (2000). Quality control limits for broth microdilution susceptibility tests of 10 antifungal agents. Journal of Clinical Microbiology 38, 34579.
3 . National Committee for Clinical Laboratory Standards. (1997). Reference Method for Broth Dilution Antifungal Susceptibility Testing of Yeasts: Approved Standard M27-A. NCCLS, Wayne, PA, USA.
4 . Rex, J. H., Pfaller, M. A., Galgiani, J. N., Bartlett, M. S., Espinel-Ingroff, A., Ghannoum, M. A. et al. (1997). Development of interpretive breakpoints for antifungal susceptibility testing: conceptual framework and analysis of in vitroin vivo correlation data for fluconazole, itraconazole, and Candida infections. Clinical Infectious Diseases 24, 23547.[ISI][Medline]
5 . Nguyen, M. H., Clancy, C. J., Yu, V. L., Yu, Y. C., Morris, A. J., Snydman, D. R. et al. (1998). Do in vitro susceptibility data predict the microbiological response to amphotericin B? Results of a prospective study of patients with Candida fungemia. Journal of Infectious Diseases 177, 42530.[ISI][Medline]
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