Background: Scopulariopsis/Microascus is a rare but devastating pathogen due to its intrinsic resistance to nearly all available antifungal agents. Microascus gracilis, an ascomycetous mould in the order Microascales, family Microascaceae, has recently emerged as a significant invasive pathogen causing opportunistic infections. Objectives and Methods: We present a case of pleural infection caused by M. gracilis with pulmonary aspergillosis in an immunocompromised man after COVID-19 pneumonia. To further understand the characteristics of the pathogen isolated from the patient, we identified the strain through mycological characteristics, matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MALDI-TOF MS) and internal transcribed spacer (ITS)-based sequencing, and performed in vitro drug susceptibility testing against common antifungal agents. Moreover, we assessed lymphocyte subsets and programmed cell death protein 1 (PD-1) expression in peripheral blood and pleural effusion to monitor the efficacy of therapy with thymosin-α-1 and intravenous immunoglobulin. Results: Filamentous fungi isolated from pleural fluid were identified as M. gracilis based on classical morphology, mass spectrometry and molecular biology methods. The susceptibility results in vitro revealed that multiple antifungal agents were inactive against the strain. Adjuvant immunomodulatory treatment successfully increased the levels of CD3+ T and CD4+ T cells while decreasing the levels of CD3+PD-1+ and CD4+PD-1+ T cells in both peripheral blood and pleural effusion. Conclusions: The immunocompromised host with opportunistic M. gracilis infection, rapid and accurate recognition through direct microscopic testing with calcofluor white and MOLDI-TOF MS, is the key to achieving a definite diagnosis, and a combination of antifungal therapy with immunomodulatory therapy is vital for improving survival.

The authors have declared no competing interest.

This work was supported by the Wuhan Health Scientifc Research Key Project (No.WX18A06), and the Wuhan Health Scientifc Research Program(No.WH21C21).

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