Epidemiological Characteristics and Antimicrobial Resistance of Prototheca Isolated in China During 2002-2024

Recently, Prototheca has emerged as a global threat to human and animal health. This study aims to characterize the epidemiological features and antimicrobial resistance profiles of Prototheca isolates in China from 2002 to 2024, thereby providing critical insights for the management and control of protothecosis.

During 2002-2024, a total of 93 Prototheca isolates were collected from human, animals and environment in China. The strain identification, in vitro antimicrobial susceptibility test, and phylogenetic reconstruction were performed.

Among all 93 Prototheca isolates, azole antifungals such as itraconazole, posaconazole, and voriconazole exhibited potent in vitro activity, with MIC₅₀ values of 1 μg/mL. Isavuconazole demonstrated superior in vitro activity, yielding geometric mean (GM) MIC and MIC₅₀ of 0.09 μg/mL and 0.06 μg/mL, respectively. Similarly, amphotericin B showed strong activity, with MIC₅₀ of 0.5 μg/mL. Among antibacterial agents, levofloxacin, tigecycline, and gentamicin showed modest activity. Isavuconazole, itraconazole, posaconazole, and voriconazole exhibited significantly greater activity against P. ciferrii than against P. bovis and P. wickerhamii. P. wickerhamii isolates constituted the predominant clade, which exhibited a highly complex branching topology.

Amphotericin B and isavuconazole exhibit superior anti-Protothecal activity against isolates from both human and bovine mastitis; however, significant inter-species differences in drug susceptibility exist.