title: Short communication: an in vitro assessment of the antibacterial activity of plant-derived oils.
abstract: Nonantibiotic treatments for mastitis are needed in organic dairy herds. Plant-derived oils may be useful but efficacy and potential mechanisms of action of such oils in mastitis therapy have not been well documented. The objective of the current study was to evaluate the antibacterial activity of the plant-derived oil components of Phyto-Mast (Bovinity Health LLC, Narvon, PA), an herbal intramammary product, against 3 mastitis-causing pathogens: Staphylococcus aureus, Staphylococcus chromogenes, and Streptococcus uberis. Plant-derived oils evaluated were Thymus vulgaris (thyme), Gaultheria procumbens (wintergreen), Glycyrrhiza uralensis (Chinese licorice), Angelica sinensis, and Angelica dahurica. Broth dilution testing according to standard protocol was performed using ultrapasteurized whole milk instead of broth. Controls included milk only (negative control), milk + bacteria (positive control), and milk + bacteria + penicillin-streptomycin (antibiotic control, at 1 and 5% concentrations). Essential oil of thyme was tested by itself and not in combination with other oils because of its known antibacterial activity. The other plant-derived oils were tested alone and in combination for a total of 15 treatments, each replicated 3 times and tested at 0.5, 1, 2, and 4% to simulate concentrations potentially achievable in the milk within the pre-dry-off udder quarter. Thyme oil at concentrations ≥2% completely inhibited bacterial growth in all replications. Other plant-derived oils tested alone or in various combinations were not consistently antibacterial and did not show typical dose-response effects. Only thyme essential oil had consistent antibacterial activity against the 3 mastitis-causing organisms tested in vitro. Further evaluation of physiological effects of thyme oil in various preparations on mammary tissue is recommended to determine potential suitability for mastitis therapy.
authors.affiliation: Department of Animal Science, North Carolina State University, Raleigh 27695.
authors.forename: K A E
authors.initials: KA
authors.lastname: Mullen
authors.affiliation: Department of Population Health and Pathobiology, North Carolina State University, Raleigh 27607.
authors.forename: A R
authors.initials: AR
authors.lastname: Lee
authors.affiliation: Department of Population Health and Pathobiology, North Carolina State University, Raleigh 27607.
authors.forename: R L
authors.initials: RL
authors.lastname: Lyman
authors.affiliation: Department of Biological Sciences, Campbell University, Buies Creek, NC 27506.
authors.forename: S E
authors.initials: SE
authors.lastname: Mason
authors.affiliation: Department of Animal Science, North Carolina State University, Raleigh 27695.
authors.forename: S P
authors.initials: SP
authors.lastname: Washburn
authors.affiliation: Department of Population Health and Pathobiology, North Carolina State University, Raleigh 27607. Electronic address: kevin_anderson@ncsu.edu.
authors.forename: K L
authors.initials: KL
authors.lastname: Anderson
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002417:Cattle; D005260:Female; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000382:microbiology; D008414:Mastitis, Bovine / Q000188:drug therapy / Q000382:microbiology; D008892:Milk / Q000382:microbiology; D009822:Oils, Volatile / Q000494:pharmacology; D010938:Plant Oils / Q000494:pharmacology*; D013210:Staphylococcus / Q000187:drug effects; D013211:Staphylococcus aureus / Q000187:drug effects; D013291:Streptococcus / Q000187:drug effects; D046930:Thymus Plant / Q000737:chemistry
chemical_list: D000900:Anti-Bacterial Agents; D009822:Oils, Volatile; D010938:Plant Oils
keywords: alternative to antibiotics; mastitis; organic; plant-derived oils