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Antimicrobial Agents and Chemotherapy, November 2007, p. 4077-4084, Vol. 51, No. 11
0066-4804/07/$08.00+0 doi:10.1128/AAC.00602-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Effect of Caspofungin on Metabolite Profiles of Aspergillus Species Determined by Nuclear Magnetic Resonance Spectroscopy
R. Plummer,1
J. Bodkin,1,
D. Power,2
N. Pantarat,2
W. A. Bubb,1
P. W. Kuchel,1 and
T. C. Sorrell2*
School of Molecular & Microbial Biosciences, University of Sydney, Sydney, NSW 2006, Australia,1 Centre for Infectious Diseases & Microbiology and Centre of Clinical Research Excellence in Infections and Bioethics in Haematological Malignancies, University of Sydney, Westmead, NSW 2145, Australia2
Received 8 May 2007/ Returned for modification 2 July 2007/ Accepted 21 August 2007
Invasive aspergillosis remains a potentially life-threatening infection, the incidence of which is increasing. Current methods used to determine the susceptibilities of Aspergillus strains to antifungal drugs are often unreliable. Nuclear magnetic resonance (NMR) spectroscopy can identify the metabolic complement of microorganisms while monitoring nutrient utilization from the incubation medium. We used 600-MHz 1H NMR spectroscopy to monitor the metabolic responses of five Aspergillus species cultured in RPMI 1640-2% glucose-morpholinepropanesulfonate buffer to various concentrations of the antifungal drugs amphotericin B (AMB) and caspofungin. The metabolic endpoint (MEP) was determined from nutrient and metabolite resonances, measured as a function of the drug concentration, and was defined as a 
50% reduction in nutrient consumption or metabolite production. MICs were evaluated by a modification of Clinical and Laboratory Standards Institute broth microdilution method M27-A, and minimal effective concentrations (MECs) were determined by microscopic examination of fungal hyphae. For AMB, the MEPs coincided with the MICs. For caspofungin, the MEPs agreed with the MECs for several Aspergillus strains, but the effect of drug pressure was more complex for others. Expansion of the MEP definition to include any significant changes in metabolite production resulted in agreement with the MEC in most cases. Paradoxical metabolic responses were observed for several Aspergillus strains at either high or low caspofungin concentrations and for one Aspergillus terreus strain with AMB. NMR spectroscopy proved to be a powerful tool for detecting the subtle effects of drug pressure on fungal metabolism and has the potential to provide an alternative method for determining the susceptibilities of Aspergillus species to antifungal drugs.
* Corresponding author. Mailing address: Centre for Infectious Diseases and Microbiology, Rm. 3114, ICPMR Bldg., Westmead Hospital, Darcy Road, Westmead, NSW 2145, Australia. Phone: 61 2 9845 6012. Fax: 61 2 9891 5317. E-mail: tania_sorrell{at}wmi.usyd.edu.au
Published ahead of print on 4 September 2007.
Present address: School of Chemistry, University of New South Wales, Kensington, NSW, Australia.
Antimicrobial Agents and Chemotherapy, November 2007, p. 4077-4084, Vol. 51, No. 11
0066-4804/07/$08.00+0 doi:10.1128/AAC.00602-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
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