The aim of the study was to evaluate the
effect of essential oils obtained from Thymus vulgaris
L., Origanum vulgare L., Origanum majerana L.,
Mentha 9 piperita L. and Allium ursinum L. against
Prototheca zopfii strains that cause inflammation of
the udder (mastitis) in cows. The study was conducted
on ten strains derived from milk samples. The
microdilution method was used to determine the
sensitivity of P. zopfii strains to the studied essential
oils, and the disk diffusion method was used to
determine the sensitivity to antifungal chemotherapeutics.
The plates were incubated for 48 h at 37 �C
under aerobic conditions. All strains of algae were
sensitive to the essential oils marjoram, thyme and
oregano and resistant to mint and garlic oils. MIC
values ranged from 0.25 to 1 ll/ml. Marjoram oil
demonstrated the greatest activity, and oregano oil the
weakest. Among the antifungal agents tested, 90% of
strains showed sensitivity to nystatin. One of the tested
strains (71/IV) was resistant to all investigated antifungal
agents. The tested essential oils are known to
have anti-algae activity and can be used as natural
agents for prophylaxis in animals, particularly in
mastitis-affected cows.