Čabarkapa, IvanaVarga, AnaPlavšić, DraganaŠarić, LjubišaTomičić, ZoricaTodorić, Olja2023-07-152023-07-152022-06Čabarkapa, I.; Varga, A.; Plavšić, D.; Šarić, Lj., Tomičić, Z.; Todorić, O. Antimicrobial activity essential oil of Origanum heracleoticun against Prototheca bovis. Abstract book of The 7th International Scientific Meeting: Mycology, Mycotoxicology, and Mycoses, 2 – 3 June 2022, Novi Sad, Serbia, 73.978-86-7946-387-6http://oa.fins.uns.ac.rs/handle/123456789/283Prototheca is a unicellular, achlorophyllous yeast-like microalga. The most important animal disease caused by Prototheca is bovine mastitis. The outbreaks of bovine mastitis caused by Prototheca bovis (formerly P. zopfii gen. 2) have been reported in several countries including Serbia. Bovine protothecosis is a serious therapeutic problem given that Prototheca has proven highly resistant to common drugs used for the treatment of mastitis. Therefore, an outbreak of protothecosis in dairy cows may lead to very significant economic losses. The objective of this study was to determine the antimicrobial activity of O. heracleoticum essential oil against five mastitis-associated strains of P. bovis. In addition, this study determined antimycotic and antibiotic susceptibility patterns of P. bovis. The following antibiotics and antifungal agents were tested: ampicillin (AMP10), gentamicin (GEN10), streptomycin, (STR10), clindamycin (DA2), fluconazole (FLU25), econazole (ECN10), clotrimazole (CLO50), miconazole (MCL10), itraconazole (ITC50), ketoconazole (KCA10), voriconasole (VO10), nystatin (NY100IU), and amphotericin B (AMB20). Essential oil of O. heracleoticum inhibited the activity of P. bovis strains, with minimal inhibition concentration (MIC) of 0.156 µL/mL and with minimal cidal concentration (MCC) of 0.625 µL/mL. Strains of P. bovis were found to be highly resistant to most of the recommended antimicrobials used against bacteria and fungi. From a total of 12 antimicrobials only nystatin, amphotericin B, gentamicin, and streptomycin were found to be effective against all P. bovis strains. Obtained results revealed that the tested EO of O. heracleoticum possesses remarkable antimicrobial activities and could be used in the development of pharmaceutical formulation as an alternative to conventional antibioticantimycotic therapy. Key words: Prototheca bovis, antimicrobial activity, essential oil, mastitisenopenAccessPrototheca bovisantimicrobial activity,essential oilmastitisOther