Abstract:
Prototheca 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, mastitis
