A novel method for identifying and distinguishing Cryptococcus neoformans and Cryptococcus gattii by surface-enhanced Raman scattering using positively charged silver nanoparticles

Shan Hu,Zhe Zhou,Jia Li,Feng Gu,Jian Yang,Chongwen Wang,Min Chen,Ying Yang,Guangyu Wang

doi:10.1038/s41598-020-68978-0

Abstract

There are approximately 1 million cryptococcal infections per year among HIV+ individuals, resulting in nearly 625,000 deaths. Cryptococcus neoformans and Cryptococcus gattii are the two most common species that cause human cryptococcosis. These two species of Cryptococcus have differences in pathogenicity, diagnosis, and treatment. Cryptococcal infections are usually difficult to identify because of their slow growth in vitro. In addition, the long detection cycle of Cryptococcus in clinical specimens makes the diagnosis of Cryptococcal infections difficult. Here, we used positively charged silver nanoparticles (AgNPs+) as a substrate to distinguish between C. neoformans and C. gattii in clinical specimens directly via surface-enhanced Raman scattering (SERS) and spectral analysis. The AgNPs+ self-assembled on the surface of the fungal cell wall via electrostatic aggregation, leading to enhanced SERS signals that were better than the standard substrate negatively charged silver nanoparticles (AgNPs). The SERS spectra could also be used as a sample database in the multivariate analysis via orthogonal partial least-squares discriminant analysis. This novel SERS detection method can clearly distinguish between the two Cryptococcus species using principal component analysis. The accuracy of the training data and test data was 100% after a tenfold crossover validation.

Highlights

There are approximately 1 million cryptococcal infections per year among HIV+ individuals, resulting in nearly 625,000 deaths
A report by the United Nation’s HIV/AIDS (Human Immunodeficiency Virus/Acquired Immunodeficiency Syndrome) program and the World Health Organization in December 2018 showed that 37.9 million people were living with HIV/AIDS; 1.7 million individuals were newly infected with the disease in 2018, and 770,000 died of AIDS-related causes
In 2002, Kwon-Chung et al.[4] found that there were some differences in phenotype, biology, and genetic taxonomy between C. neoformans and C. neoformans var. gattii ; C. gattii was reclassified as a single species

Summary

Introduction

There are approximately 1 million cryptococcal infections per year among HIV+ individuals, resulting in nearly 625,000 deaths. Cryptococcus neoformans and Cryptococcus gattii are the two most common species that cause human cryptococcosis These two species of Cryptococcus have differences in pathogenicity, diagnosis, and treatment. We used positively charged silver nanoparticles ( AgNPs+) as a substrate to distinguish between C. neoformans and C. gattii in clinical specimens directly via surface-enhanced Raman scattering (SERS) and spectral analysis. The SERS spectra could be used as a sample database in the multivariate analysis via orthogonal partial least-squares discriminant analysis This novel SERS detection method can clearly distinguish between the two Cryptococcus species using principal component analysis. Traditional detection methods for cryptococcus, such as ink staining and antigen kit testing, are relatively fast but cannot distinguish between C. neoformans and C. gattii[2,5]. This is true for cryptococcus—a special fungal pathogen that contains a c apsule[15,16]

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Discussion

Conclusion