Purpose: Monitoring antifungal susceptibility patterns for new or established antifungals is imperative. Antifungal resistance is frequent in molds, frequently leading to invasive mold infections (IMIs) in immunocompromised patients with high morbidity and mortality. Limited availability of effective antifungals for treatment of IMIs in China is an enormous challenge. The purpose of this study was to monitor in vitro antifungal resistance profiles of mold isolates from China, with a particular focus on evaluating in vitro isavuconazole (ISA) activity against these isolates, contributing to the treatment guidance in clinics.
Methods: We evaluated the in vitro activity of ISA and its comparators (voriconazole [VOR] and amphotericin B [AMB]) against 131 clinical isolates of Aspergillus spp. (n = 105) and Mucorales order (n = 26) collected between 2017 and 2020 from China.
Results: ISA and VOR exhibited similar in vitro activity against Aspergillus spp., with minimum inhibitory concentration (MIC)₅₀ of 1 μg/mL and MIC₉₀ of 2 μg/mL, respectively. Overall, AMB was less active than azoles against Aspergillus spp. (MIC₅₀: 4 μg/mL, MIC₉₀: 8 μg/mL). Against the Mucorales order, ISA demonstrated MIC₅₀ of 0.5 μg/mL and MIC₉₀ of 1 μg/mL; however, one strain each of Mucor circinelloides and Syncephalastrum racemosum were resistant to ISA (MICs: > 8 μg/mL). VOR exhibited little or no activity (MIC₅₀: 8 μg/mL, MIC₉₀: > 8 μg/mL) against the Mucorales order, whereas AMB had MIC₅₀ and MIC₉₀ of 1 μg/mL.
Conclusion: This was the first multicenter, in vitro study conducted in China and demonstrated the excellent activities of ISA against most species of the Mucorales order. MIC indicated an advantage over currently available azole antifungals, positioning ISA as a potential alternative to VOR for clinical management of IMIs. As with other antimicrobials, clinicians should employ stewardship and best practices in relation to potential resistance to new azole antifungals.
Keywords: Mucorales order, Aspergillus species, antifungal susceptibility testing, isavuconazole, resistance