Monoclonal Antibodies Can Aid in the Culture-Based Detection and Differentiation of Mucorales Fungi—The Flesh-Eating Pathogens Apophysomyces and Saksenaea as an Exemplar

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Background: The frequency of necrotising cutaneous and soft tissue infections caused by the Mucorales fungi Apophysomyces and Sakasenaea is increasing. The absence of sophisticated diagnostic technologies in low- and middle-income countries (LMICs) means that detection of cutaneous mucormycosis continues to rely on culture of the infecting pathogens from biopsy and their differentiation based on morphological characteristics. However, Apophysomyces and Sakasenaea are notorious for their failure to sporulate on standard mycological media used for the identification of human pathogenic fungi. Differentiation of these pathogens and their discrimination from Aspergillus fumigatus, the most common mould pathogen of humans, is essential due to their differing sensitivities to the antifungal drugs used to treat mucormycosis. Methods: A murine IgG1 monoclonal antibody, JD4, has been developed that is specific to Apophysomyces species. In Western blotting and enzyme-linked immunosorbent assay (ELISA), mAb JD4 is shown to bind to an extracellular 15 kDa protein, readily detectable in crude antigen extracts from non-sporulating cultures of Apophysomyces. Results: When combined with a Mucorales-specific lateral-flow immunoassay (LFIA), mAb JD4 allows the differentiation of Apophysomyces from Saksenaea species and discrimination from Aspergillus fumigatus. Monoclonal antibody JD4 enables the detection and differentiation of Apophysomyces species from other fungal pathogens that cause rapidly progressive cutaneous and soft tissue mycoses in humans. When this is combined with a rapid LFIA, improvements are offered in the sensitivity and specificity of Mucorales detection based on mycological culture, which remains a gold-standard procedure for mucormycosis detection in LMICs lacking access to more sophisticated diagnostic procedures.

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