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J Med Microbiol 53 (2004), 1201-1206; DOI: 10.1099/jmm.0.45742-0
© 2004 Society for General Microbiology
ISSN 0022-2615

Quantification and assessment of viability of Cryptococcus neoformans by LightCycler amplification of capsule gene mRNA

Muhammad Amjad1, Najla Kfoury1, Raymond Cha2,4 and Reem Mobarak3

1,2Clinical Laboratory Science Program1 and Department of Pharmacy Practice2, Eugene Applebaum College of Pharmacy and Health Services, Wayne State University, 259 Mack Avenue, Detroit, MI 48201, USA 3,4Medical Research Program3 and School of Medicine4, Wayne State University, 540 E. Canfield Street, Detroit, MI 48201, USA

Correspondence Muhammad Amjad m.amjad{at}wayne.edu

Received May 11, 2004
Accepted August 12, 2004

Cryptococcus neoformans is an opportunistic fungal pathogen. It infects the central nervous system causing meningitis, which is fatal if untreated, especially in AIDS and immunosuppressed patients. In this study a method of quantification and assessment of viability of C. neoformans by LightCycler RT-PCR amplification of the capsule gene mRNA is established. The sequence of primers and probes were derived from C. neoformans capsular CAP10 gene mRNA (GenBank accession number AF144574), and were species specific. Agarose gel electrophoresis analysis of LightCycler RT-PCR product showed a single band of 223 bp in length. In order to develop an internal control a 223 bp exon fragment of capsule mRNA was cloned in the pCR2.1 plasmid vector and RNA was generated by in vitro transcription. To determine the sensitivity of the assay, serial dilutions of in vitro-transcribed RNA with known concentrations and copy numbers, and serially diluted cultures of viable and nonviable C. neoformans were used. Under optimal conditions as little as 0.472 fg of capsule mRNA could be detected, corresponding to 1–10 c.f.u. ml–1 of the sample. No amplification was observed from up to105 heat/UV radiation-killed yeast cells and RNA of other bacterial and fungal pathogens and human genomic DNA or RNA. The amplification of capsule mRNA represents a sensitive, specific and quantitative means of detection of viable C. neoformans in clinical specimens and can be useful in the evaluation of the therapeutic efficacy of antifungal drugs in the treatment of C. neoformans meningitis.






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