渡辺 哲

BACKGROUND: Azoles target Cyp51A and Cyp51B in Aspergillus fumigatus. Mutations in cyp51A are known as the primary mechanisms of azole resistance. However, not all of them cause azole resistance. Among them, mutations related to improved susceptibility have not been reported so far. We found that two isolates that carry frameshift or nonsense mutations in cyp51A are more susceptible to azoles, even to fluconazole (FLCZ) (IC50: frameshift, 32 μg/mL; nonsense, 32 μg/mL) compared to other azole-susceptible strains (IC50: > 256 μg/mL). OBJECTIVES: We investigated the contribution of these two mutations to azole sensitivity and their effect on Cyp51A functions. METHODS: We transformed an experimental strain, AfS35, by replacing cyp51AWT with each of the mutated cyp51A and measured its MICs to azoles. We also evaluated the functions of mutated Cyp51A after suppression of Cyp51B, based on the notion that Cyp51A and Cyp51B complement each other. RESULTS: Induction of mutated cyp51A in AfS35 led to higher susceptibility to FLCZ (IC50: frameshift, 32-64 μg/mL; nonsense, 32 μg/mL). Transformants carrying either of the mutated cyp51A could not survive when cyp51B was suppressed, indicating that these cyp51A mutations result in Cyp51A dysfunction. Furthermore, a cyp51A-deleted mutant strain also showed increased susceptibility to FLCZ (IC50: 32 μg/mL), similar to cyp51A dysfunctional strains, while a cyp51B-deleted mutant strain showed unchanged susceptibility (IC50: > 256 μg/mL) from AfS35. CONCLUSIONS: It was suggested that FLCZ can inhibit Cyp51B rather than Cyp51A and that this unequal inhibition leads to higher azole susceptibility of the two isolates harbouring Cyp51A dysfunction.

Abstract Allodiploid hybrid species,Aspergillus latus, belonging to sectionNidulantes, is a hybrid ofA. spinulosporusand unknown species closely related toA. quadrilineatusandA. subltus. This hybrid has often been misidentified as the species in sectionNidulantes, such asA. nidulans,A. spinulosporus,A. sublatus, or other cryptic species. A. latushas not been reported in Japan as well as Asia so far. In this study, we screened 23 clinical strains identified asA. spinulosporusisolated in Japan from 2012 to 2023 and found sevenA. latusstrains. To characterize theA. latusstrains, we conducted comprehensive phenotyping including morphological observation, whole genome sequences and phylogenetic analysis based on calmodulin (CaM) gene. In addition, we conducted antifungal susceptibility testing forA. latusstrains. As a result, the morphological characters ofA. latuswere more similar to those ofA. spinulosporuscompared toA. sublatus. However, the ascospore ofA. latusdiffered from that ofA. spinulosporus.A. latusphylogenetically clustered withA. spinulosporusandA. sublatus. Furthermore,A. latusstrains showed reduced susceptibility to caspofungin and amphotericin B compared toA. spinulosporus, while they were susceptible to azoles. Our results suggest thatA. latushas been a causative pathogen of aspergillosis in Japan since 2013.

Schizophyllum commune is the third most common causative fungus of allergic bronchopulmonary mycosis(ABPM). Two-thirds of ABPM caused by S. commune can be positive for Aspergillus fumigatus-specific IgE, which can be difficult to diagnose. Our patient presented to our hospital with wet cough for 3 months and chest pain for 3 days. Blood tests showed IgE 1522 IU/mL, eosinophils 688/mm3, A. fumigatus -specific IgE 2.24 UA/mL, and chest computed tomography showed high-attenuation mucus. Bronchoscopy showed mucus plugs and speculum examination showed filamentous fungi, but various culture tests did not detect A. fumigatus, Asp f 1-specific IgE was negative, and S. commune was detected in the culture of bronchial washing. Since he was positive for S. commune-specific IgE and IgG, he diagnosed ABPM caused by S. commune. These findings demonstrate the importance of identifying the causative fungus in ABPM by detailed examination.

Pediatric myelodysplasia syndrome is often characterized by hypoplastic bone marrow morphology and predisposition to infection. Invasive aspergillosis during hematopoietic stem cell transplantation poses a significant threat and often requires voriconazole (VRCZ) therapy. However, difficulties in achieving appropriate VRCZ blood levels due to drug interactions have prompted the exploration of alternative treatments, such as isavuconazole (ISCZ). We present the case of a 4-year-old boy with myelodysplasia syndrome who developed multiple abscesses, including a brain abscess caused by Aspergillus fumigatus, and was successfully treated with ISCZ. Despite initial treatment with liposomal amphotericin B and VRCZ, the patient's condition deteriorated. Transitioning to ISCZ treatment resulted in significant clinical improvement, resolution of the abscesses, and reduced antigen levels. Although ISCZ induced hepatic enzyme elevation, supportive care improved without discontinuation of treatment. This case highlights the potential of ISCZ in cases of pediatric invasive aspergillosis where traditional therapies fail, underscoring the need for further research and formulation development to optimize its use in this population. As more cases accumulate, ISCZ may become a promising option for treating severe invasive aspergillosis in pediatric patients undergoing hematopoietic stem cell transplantation.