A Rapid, Visible, and Highly Sensitive Method for Recognizing and Distinguishing Invasive Fungal Infections via CCP-FRET Technology

Invasive fungal infection (IFI) is one of the leading causes of death in the intensive care unit (ICU) due to its high morbidity and mortality among immunocompromised patients. Early diagnosis of IFI is typically infeasible because of the lack of clinical signs and symptoms. By virtue of the cationic conjugated polymer-based fluorescence resonance energy transfer (CCP-FRET) technology, we develop a rapid, visible, simple, and sensitive method for simultaneous detection and discrimination of three types of pathogens, including Candida albicans (C. albicans), Klebsiella pneumoniae (K pneumoniae), and Cryptococcus neoformans (C. neoformans). The CCP-FRET system contains a CCP fluorescent probe and pathogen-specific DNA labeled with fluorescent dyes. These two components spontaneously self- assemble into the complex under electrostatic attraction, resulting in an efficient FRET from CCP to fluorescent dyes when irradiated with a 380 nm ultraviolet (UV) light. The CCP-FRET method can specifically identify the DNA molecules that are extracted from culture pathogen strains or blood samples via PCR and single base extension (SBE) reactions, without any cross- reactions on the DNA of nonspecific strains. In particular, the sensitivity of this method is down to 0.03125 ng, which is ten times higher than that of real-time PCR. We further evaluate its detection efficiency by testing 15 blood samples from neonatal patients who suffer from pathogen infections, in which some of them have undergone antipathogen treatments. Using the CCP-FRET method, 33.3% (5/15) of samples tested positive for C albicans and/or K. pneumoniae infections, whereas no pathogen DNAs are recognized with real-time PCR, despite using the same primers. Interestingly, the CCP-FRET method can output unique fluorescent color as well as RGB patterns to different types of pathogen infections, by which the infection type can be conveniently determined. Collectively, the CCP-FRET method is a sensitive and reliable detection platform for rapid identification of fungal and bacterial multiple infections, holding great promise for uses in clinical testing.