Protothecosis is an infectious disease of animals and humans. In animals, the most common clinical presentation is bovine mastitis protothecosis. Bovine mammary infection by P. zopfii determines commonly clinical mastitis, which progress to pyogranulomatous processes of difficult tissue resolution. At this moment there are no effective therapy for mammary protothecosis in cattle. Due to the high transmissibility of the microorganism, both in the milking as environment, as well absence of effective therapy, control of disease has been supported by the segregation of affected animals, by chemical ablation (drying) of the teats, or even in culling of animals. Different researchers have studied many chemical products, "in vitro" and "in vivo", (antimicrobials, disinfectants, antiseptics and algaecides) against strains of the Prototheca genus, with low efficiency or, at least, controversial results. In this context, this study aims to investigate the "in vitro" sensitivity of the P. zopfii isolates ("minimum algaecide concentration" - MAC) against to ozone (O3) and guanidine. Approximately 50 P. zopfii isolates obtained from cows with clinical or subclinical mastitis will be used. The P. zopfii strains will be classified based on morphological, biochemical and culture characteristics. The MAC, based on minimal bactericidal concentration, will be considered as the lowest dilution (concentration) of the drug or chemical product able of preventing the multiplication of algae, after microbiological culture on bovine blood agar. In the literature consulted, there are no studies assessing the "in vitro" efficacy of ozone (O3) and guanidine against P. zopfii strains isolated from bovine mastitis.
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