Emergence of cryptic <i>Aspergillus</i> species infection and importance of antifungal susceptibility testing

Abstract

Background: Amongst the list of >360 Aspergillus species, A. fumigatus, A. flavus, A. terreus and A. niger are the predominant species that cause human infection, but the clinical spectrum of Aspergillus infections has progressively diversified, largely due to the advancement of molecular technologies, which revealed numerous clinical isolates to be cryptic species. Currently, there is a lack of knowledge on the types of disease that these cryptic species cause. Moreover, these cryptic species may exhibit dissimilar antifungal susceptibilities to the four predominant Aspergillus species. Materials/methods: All Aspergillus strains isolated in this study were recovered from clinical specimens from five hospitals in Hong Kong, Shenzhen and Shanghai. Sequencing of two long-established markers, beta-tubulin and/or calmodulin genes was performed to ensure accurate species identification. Antifungal susceptibility testing was performed to investigate the susceptibility pattern of these cryptic species against 10 antifungal agents by the EUCAST reference protocol. Results: During 2012–2018, 21 clinical strains from 21 patients aged 26-78 years (male:female ratio = 2:1) were found belonging to twelve cryptic Aspergillus species (A. tubingensis [n = 4], A. caelatus [n = 3], A. amoenus [n = 2], A. brunneoviolaceus [n = 2], A. sydowii [n = 2], A. tamarii [n = 2], A. aculeatus [n = 1], A. austroafricanus [n = 1], A. nidulans [n = 1], A. neoniger [n = 1], A. quadrilineatus [n = 1], A. welwitschaie [n = 1]). Sixteen of the patients (76.2%) were burdened with underlying disease related to chronic respiratory diseases (56.2%). Infection manifested as a broad-spectrum of diseases mainly comprising of chronic pulmonary aspergillosis (33.3%), chronic otitis media (9.5%), invasive aspergillosis (9.5%), wound infection (9.5%) and onychomycosis (9.5). Susceptibility testing showed elevated azole MICs for A. tubingensis and A. neoniger (isavuconazole: 2 to >16 mg/L; voriconazole: 2 to >16 mg/L; itraconazole: 1 to >8 mg/L; posaconazole: 0.125 to 2 mg/L). Conclusions: Our results demonstrated a diverse spectrum of cryptic Aspergillus species infection and the potential emergence of antifungal resistance. Accurate identification of clinical Aspergillus isolates and in vitro antifungal susceptibility testing are crucial for better patient management.