Skip to main content
PMC home page
Journal of Clinical Microbiology logoLink to Journal of Clinical Microbiology
. 1995 May;33(5):1302–1307. doi: 10.1128/jcm.33.5.1302-1307.1995

Effect of increasing inoculum sizes of pathogenic filamentous fungi on MICs of antifungal agents by broth microdilution method.

A Gehrt 1, J Peter 1, P A Pizzo 1, T J Walsh 1
PMCID: PMC228150  PMID: 7615745

Abstract

Inoculum size is a critical variable in development of methods for antifungal susceptibility testing for filamentous fungi. In order to investigate the influence of different inoculum sizes on MICs of amphotericin B, 5-fluorocytosine, itraconazole, and miconazole, 32 clinical isolates (8 Aspergillus fumigatus, 8 Aspergillus flavus, 5 Rhizopus arrhizus, 8 Pseudallescheria boydii, and 3 Fusarium solani isolates) were studied by the broth microdilution method. Four inoculum sizes were studied: 1 x 10(2) to 5 x 10(2), 1 x 10(3) to 5 x 10(3), 1 x 10(4) to 5 x 10(4), and 1 x 10(5) to 5 x 10(5) CFU/ml. The National Committee for Clinical Laboratory Standards reference method for antifungal susceptibility testing in yeasts was modified and applied to filamentous fungi. The inoculum was spectrophotometrically adjusted, and all tests were performed in buffered medium (RPMI 1640) at pH 7.0 with incubation at 35 degrees C for 72 h. MICs were read at 24, 48, and 72 h. Amphotericin B showed a minimum effect of inoculum size on MICs for all species with the exception of P. boydii (P < 0.05). A significant effect of inoculum size on MICs was observed with 5-fluorocytosine, for which there was an increase of more than 10-fold in MICs against all Aspergillus spp. between inoculum concentrations of 10(2) and 10(4) CFU/ml (P < 0.001). For itraconazole, the results showed a more species-dependent increase of MICs, most strikingly for R. arrhizus and P. boydii. Miconazole, which was tested only with P. boydii, did not demonstrate a significant effect of inoculum size on MICs.(ABSTRACT TRUNCATED AT 250 WORDS)

Full Text

The Full Text of this article is available as a PDF (254.4 KB).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Anaissie E., Bodey G. P., Kantarjian H., Ro J., Vartivarian S. E., Hopfer R., Hoy J., Rolston K. New spectrum of fungal infections in patients with cancer. Rev Infect Dis. 1989 May-Jun;11(3):369–378. doi: 10.1093/clinids/11.3.369. [DOI] [PubMed] [Google Scholar]
  2. Brook I. Inoculum effect. Rev Infect Dis. 1989 May-Jun;11(3):361–368. doi: 10.1093/clinids/11.3.361. [DOI] [PubMed] [Google Scholar]
  3. Cook R. A., McIntyre K. A., Galgiani J. N. Effects of incubation temperature, inoculum size, and medium on agreement of macro- and microdilution broth susceptibility test results for yeasts. Antimicrob Agents Chemother. 1990 Aug;34(8):1542–1545. doi: 10.1128/aac.34.8.1542. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Denning D. W., Stevens D. A. Antifungal and surgical treatment of invasive aspergillosis: review of 2,121 published cases. Rev Infect Dis. 1990 Nov-Dec;12(6):1147–1201. doi: 10.1093/clinids/12.6.1147. [DOI] [PubMed] [Google Scholar]
  5. Espinel-Ingroff A., Kerkering T. M. Spectrophotometric method of inoculum preparation for the in vitro susceptibility testing of filamentous fungi. J Clin Microbiol. 1991 Feb;29(2):393–394. doi: 10.1128/jcm.29.2.393-394.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Espinel-Ingroff A., Kish C. W., Jr, Kerkering T. M., Fromtling R. A., Bartizal K., Galgiani J. N., Villareal K., Pfaller M. A., Gerarden T., Rinaldi M. G. Collaborative comparison of broth macrodilution and microdilution antifungal susceptibility tests. J Clin Microbiol. 1992 Dec;30(12):3138–3145. doi: 10.1128/jcm.30.12.3138-3145.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Francis P., Walsh T. J. Approaches to management of fungal infections in cancer patients. Oncology (Williston Park) 1992 May;6(5):133-44; discussion 144, 147-8. [PubMed] [Google Scholar]
  8. Fromtling R. A., Galgiani J. N., Pfaller M. A., Espinel-Ingroff A., Bartizal K. F., Bartlett M. S., Body B. A., Frey C., Hall G., Roberts G. D. Multicenter evaluation of a broth macrodilution antifungal susceptibility test for yeasts. Antimicrob Agents Chemother. 1993 Jan;37(1):39–45. doi: 10.1128/aac.37.1.39. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Patterson T. F., Andriole V. T., Zervos M. J., Therasse D., Kauffman C. A. The epidemiology of pseudallescheriasis complicating transplantation: nosocomial and community-acquired infection. Mycoses. 1990 Jun;33(6):297–302. [PubMed] [Google Scholar]
  10. Pfaller M. A., Burmeister L., Bartlett M. S., Rinaldi M. G. Multicenter evaluation of four methods of yeast inoculum preparation. J Clin Microbiol. 1988 Aug;26(8):1437–1441. doi: 10.1128/jcm.26.8.1437-1441.1988. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Pfaller M. A., Rinaldi M. G. Antifungal susceptibility testing. Current state of technology, limitations, and standardization. Infect Dis Clin North Am. 1993 Jun;7(2):435–444. [PubMed] [Google Scholar]
  12. Pfaller M. A., Rinaldi M. G., Galgiani J. N., Bartlett M. S., Body B. A., Espinel-Ingroff A., Fromtling R. A., Hall G. S., Hughes C. E., Odds F. C. Collaborative investigation of variables in susceptibility testing of yeasts. Antimicrob Agents Chemother. 1990 Sep;34(9):1648–1654. doi: 10.1128/aac.34.9.1648. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Reuben A., Anaissie E., Nelson P. E., Hashem R., Legrand C., Ho D. H., Bodey G. P. Antifungal susceptibility of 44 clinical isolates of Fusarium species determined by using a broth microdilution method. Antimicrob Agents Chemother. 1989 Sep;33(9):1647–1649. doi: 10.1128/aac.33.9.1647. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Rex J. H., Pfaller M. A., Rinaldi M. G., Polak A., Galgiani J. N. Antifungal susceptibility testing. Clin Microbiol Rev. 1993 Oct;6(4):367–381. doi: 10.1128/cmr.6.4.367. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Stratton C. W. Bactericidal testing. Infect Dis Clin North Am. 1993 Jun;7(2):445–459. [PubMed] [Google Scholar]
  16. Walsh T. J., Lee J. W., Roilides E., Pizzo P. A. Recent progress and current problems in management of invasive fungal infections in patients with neoplastic diseases. Curr Opin Oncol. 1992 Aug;4(4):647–655. doi: 10.1097/00001622-199208000-00008. [DOI] [PubMed] [Google Scholar]

Articles from Journal of Clinical Microbiology are provided here courtesy of American Society for Microbiology (ASM)

RESOURCES