Abstract

Background: Bovine mastitis caused by Prototheca spp. is the most significant animal disease of algal origin, with an increasing number of cases reported worldwide. Currently, there is no effective treatment, so control requires the culling of infected animals. In Chile, information is limited, and a discrepancy remains in the literature regarding the Prototheca species involved in bovine mastitis. Methods: This study aimed to molecularly type and phenotypically characterize Prototheca isolates associated with bovine mastitis in Chile. Sixty-six Prototheca isolates obtained from individual bovine mastitis milk samples and bulk tank milk samples were analyzed through cytochrome b gene (cytb) sequencing, Random Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR) analysis, and phenotypic evaluation (morphology, antimicrobial susceptibility, and biofilm formation). Results: Sixty-five isolates were identified as P. bovis and one as P. ciferrii, marking the first report of the latter in bovine mastitis in Chile. RAPD analysis revealed a high genetic diversity in P. bovis. All strains exhibited resistance to the antibiotics tested from the Fluoroquinolone, beta-lactam, and sulfonamide groups; however, 100% of the strains showed susceptibility to aminoglycosides, with gentamicin standing out as a potential therapeutic option. Most P. bovis strains formed weak (81.5%, 53/65) or moderate (15.4%, 10/65) biofilms, which could favor the persistence of infection. Conclusions: These findings provide novel insights into the molecular and phenotypic characteristics of Prototheca spp. in Chile, highlighting the predominance of P. bovis, the emergence of P. ciferri, and the implications for antimicrobial management and disease control.