T2 Magnetic Resonance Enables Nanoparticle-Mediated Rapid Detection of Candidemia in Whole Blood

Nanoparticles and T2 magnetic resonance allow for DNA amplification and detection of Candida species in clinical whole-blood specimens. Nanoparticle Clusters Rapidly Detect Candida Time is not on the side of patients suspected of blood infection (sepsis). Patients with bloodstream infections of Candida species are often misdiagnosed. Or, the diagnosis comes too late. These two factors contribute to a high mortality rate of 40% from this fungus. To deliver a quick and accurate diagnosis for candidemia, Neely and colleagues designed an assay that combines nanotechnology and clinical imaging. The authors developed a nano-inspired platform that detects DNA from five of the most common Candida species found in patient blood. Candida cells were first lysed mechanically, and then polymerase chain reaction primers and a polymerase-like enzyme were added to selectively amplify the released DNA. Nanoparticles with complementary “capture probes” could then bind to the amplified DNA. At that point, the free particles clustered together, allowing for detection with T2 magnetic resonance (T2MR). Neely et al. built a portable T2MR instrument for detecting the fungal DNA at the patient’s bedside. With this technology, they were able to detect down to three colony-forming units (CFU) of C. albicans and C. tropicalis per milliliter of blood; even lower limits of detection (1 to 2 CFU/ml) were observed for C. krusei, C. glabrata, and C. parapsilosis. Using whole-blood samples from 24 patients, the authors were able to correctly identify the 8 candidemic patients, without any false-positive readouts from blood samples that contained bacteria. The combination of nanoparticles and clinical MR detection allowed for specific detection of Candida species in infected patients’ blood. The T2MR readouts were even more sensitive than blood culture, showing residual Candida cells in patients undergoing treatment with antifungal medication days after blood culture tests were negative. With such portability and sensitivity, this nanoparticle platform could be used in the clinic to diagnose blood infection earlier than standard culture, thus allowing for rapid treatment of septic patients, where time is of the essence. Candida spp. cause both local and disseminated infections in immunocompromised patients. Bloodstream infections of Candida spp. , known as “candidemia,” are associated with a high mortality rate (40%), which is mainly attributed to the long diagnostic time required by blood culture. We introduce a diagnostic platform based on T2 magnetic resonance (T2MR), which is capable of sensitive and rapid detection of fungal targets in whole blood. In our approach, blood-compatible polymerase chain reaction is followed by hybridization of the amplified pathogen DNA to capture probe–decorated nanoparticles. Hybridization yields nanoparticle microclusters that cause large changes in the sample’s T2MR signal. With this T2MR-based method, Candida spp. can be detected directly in whole blood, thus eliminating the need for analyte purification. Using a small, portable T2MR detection device, we were able to rapidly, accurately, and reproducibly detect five Candida species within human whole blood with a limit of detection of 1 colony-forming unit/ml and a time to result of <3 hours. Spiked blood samples showed 98% positive agreement and 100% negative agreement between T2MR and blood culture. Additionally, performance of the assay was evaluated on 21 blinded clinical specimens collected serially. This study shows that the nanoparticle- and T2MR-based detection method is rapid and amenable to automation and offers clinicians the opportunity to detect and identify multiple human pathogens within hours of sample collection.