Evaluation of a digital microfluidic real-time PCR platform to detect DNA of Candida albicans in blood.

Abstract

Species of Candida frequently cause life-threatening infections in neonates, transplant and intensive care unit (ICU) patients, and others with compromised host defenses. The successful management of systemic candidiasis depends upon early, rapid diagnosis. Blood cultures are the standard diagnostic method, but identification requires days and less than half of the patients are positive. These limitations may be eliminated by using real-time polymerase chain reaction (PCR) to detect Candida DNA in the blood specimens of patients at risk. Here, we optimized a PCR protocol to detect 5-10 yeasts in low volumes of simulated and clinical specimens. We also used a mouse model of systemic candidiasis and determined that candidemia is optimally detectable during the first few days after infection. However, PCR tests are often costly, labor-intensive, and inconvenient for routine use. To address these obstacles, we evaluated the innovative microfluidic real-time PCR platform (Advanced Liquid Logic, Inc.), which has the potential for full automation and rapid turnaround. Eleven and nine of 16 specimens from individual patients with culture-proven candidemia tested positive for C. albicans DNA by conventional and microfluidic real-time PCR, respectively, for a combined sensitivity of 94%. The microfluidic platform offers a significant technical advance in the detection of microbial DNA in clinical specimens.

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Citation

Published Version (Please cite this version)

10.1007/s10096-012-1561-6

Publication Info

Schell, WA, JL Benton, PB Smith, M Poore, JL Rouse, DJ Boles, MD Johnson, BD Alexander, et al. (2012). Evaluation of a digital microfluidic real-time PCR platform to detect DNA of Candida albicans in blood. Eur J Clin Microbiol Infect Dis, 31(9). pp. 2237–2245. 10.1007/s10096-012-1561-6 Retrieved from https://hdl.handle.net/10161/11061.

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Scholars@Duke

Schell

Wiley Alexander Schell

Associate Professor Emeritus in Medicine
Smith

Phillip Brian Smith

Samuel L. Katz Distinguished Professor of Pediatrics

Dr. Smith completed his residency in pediatrics and a fellowship in neonatal medicine at Duke University Medical Center in 2004 and 2007, respectively. He completed an MHS in clinical research from Duke University in 2006 and an MPH in biostatistics from the University of North Carolina at Chapel Hill in 2009. His research is focused on pediatric drug safety, neonatal pharmacology, and the epidemiology of neonatal infections. Dr. Smith is or has been the protocol chair for more than 14 studies of drugs in infants and children. He is the Principal Investigator for the Environmental Influences on Child Health Outcomes (ECHO) Coordinating Center.

Benjamin

Daniel Kelly Benjamin

Kiser-Arena Distinguished Professor

Dr. Danny Benjamin is the Principal Investigator and Chair of the National Institute of Child Health and Human Development’s Pediatric Trials Network. The Network is responsible for designing and leading clinical trials of off-patent medicines in children of all ages across all therapeutic areas. The team has established, or is actively studying, the correct dosing and safety of more than 70 of the most commonly used medicines in children. Each of these trials is conducted under an Investigational New Drug (IND) application with guidance from the Food and Drug Administration for labeling.

The Pediatric Trials Network has directly impacted the healthcare of over 90% of American children.

Signature programs of the Network include clinical trials in premature, term infants, breast feeding mothers, and obese children. Over the past 10 years, Danny’s group has enrolled more premature infants, at more sites, in more clinical trials of off-patent anti-infectives under an IND than all other academic medical centers, pharmaceutical companies, and government agencies in the world, combined.

Danny is recognized by the National Institutes of Health as a premiere mentor and educator. His research program serves as a platform to train students and early career investigators. Danny’s group has a clinical research summer program for high school and college students that has a focus on trainees under-represented in medicine, and he is the primary mentor for medical students, residents, subspecialty fellows, and multiple junior faculty. He has been the primary or secondary mentor for 10 faculty who have received career development awards and who have then gone on to secure their own funding.

Danny's service to the community is expressed through his passion for coaching baseball. He has coached over 500 recreation league, travel league, and scholastic baseball games and he is the head coach of Smith Middle School, the 5-year reigning southern conference champions. Danny and his wife own a charitable non-profit that provides athletic and fitness opportunities for disadvantaged school-aged boys and girls.

Perfect

John Robert Perfect

James B. Duke Distinguished Professor of Medicine

Research in my laboratory focuses around several aspects of medical mycology. We are investigating antifungal agents (new and old) in animal models of candida and cryptococcal infections. We have examined clinical correlation of in vitro antifungal susceptibility testing and with in vivo outcome. Our basic science project examines the molecular pathogenesis of cryptococcal infections. We have developed a molecular foundation for C. neoformans, including transformation systems, gene disruptions, differential gene expression screens, and cloning pathogenesis genes. The goal of this work is to use C. neoformans as a model yeast system to identify molecular targets for antifungal drug development. There are a series of clinical trials in fungal infections which are being coordinated through this laboratory and my work also includes a series of antibiotic trials in various aspects of infections. Finally, we have now been awarded a NIH sponsored Mycology Unit for 5 years with 6 senior investigators which is focused on C. neoformans as a pathogenic model system, but will include multiple areas of medical mycology from diagnosis to treatment.

Mitchell

Thomas Greenfield Mitchell

Associate Professor Emeritus in Molecular Genetics and Microbiology

Among patients with AIDS, leukemia or other cancers, organ or bone marrow transplants, and similar immunocompromising risk factors, the incidence of opportunistic mycoses and the number of different fungal pathogens are increasing dramatically. For many of these fungi, the definition of a species and the recognition of pathogen are highly problematic. Conventional methods of identification are based on morphological and physiological characteristics and are often time-consuming, difficult to interpret, and inconsistent. This laboratory is using DNA-based methods to (i) identify fungal pathogens, (ii) resolve taxonomic issues, (iii) facilitate epidemiological studies, (iv) recognize strains with clinically relevant phenotypes, such as resistance to antifungal drugs, (v) elucidate the origin(s) of diversity and the population genetics of the major pathogens, and (vi) explore functional genomics to identify virulence factors. We have developed reliable methods to genotype strains and are analyzing gene sequences to clarify the phylogeny of controversial taxa.

To conduct rigorous population studies of Candida albicans, we developed single-locus markers based on polymorphisms of PCR products. Genotypic frequencies and segregation patterns at these loci have confirmed that C. albicans is diploid and suggest that some form of recombination occurs in this "asexual" yeast. To investigate whether separate populations of C. albicans exist in disparate geographical locations, we compared strains collected from healthy and HIV-infected persons in U.S. and Brazil. Although a number of different genotypes were recognized at each location, the same multilocus genotype was prevalent among the clinical isolates, indicating a remarkable homogeneity among these populations.

We are using DNA-based methods to compare global isolates of Cryptococcus neoformans from patients with AIDS and other sources, to analyze the distribution and relatedness of strains, to identify genotypes of clinical importance, and to create linkage map of this pathogen. To determine the source of C. neoformans in patients, we developed a genetic markers to investigate the structure of clinical and environmental populations. With analysis of quantitative trait loci, specific genotypes will be identified that represent clones that have significantly diverged with respect to clinically relevant phenotypes, including susceptibility to antifungal drugs and the expression of virulence factors. We are investigating genomic evolution and phenotypic variation in natural populations of C. neoformans. These approaches will correlate genotypes with pathobiological phenotypes, leading to beneficial and predictive information about the epidemiology, diagnosis and prognosis of cryptococcosis in patients with AIDS.


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