Plant phenolic extracts as an effective strategy to control Staphylococcus aureus, the dairy industry pathogen

Staphylococcus aureus is one of the most common contagious mastitis pathogens. Bovine mastitis is considered an important reservoir for dairy industry contamination, and therefore to ensure S. aureus control has gained a pivotal importance. Natural matrices present multiple biological effects, being its antimicrobial potential increasingly reported. Thus, the present study aims to assess the antibacterial activity of several methanol:water extracts, obtained from plants, against Staphylococcus aureus. Moreover, the most effective extract was characterized in terms of phenolic compounds, by using high performance liquid chromatography coupled to diode array and mass spectrometer detectors. Among the tested extracts, Eucalyptus globulus was the most effective against all tested S. aureus strains, followed by Juglans regia and Foeniculum vulgare. Inhibition halos of the plant extracts varied between 8.0-16.0 mm, excepting for F. vulgare in which two evident halos were observed: one with growth inhibition (5.0-7.0 mm) and a second one with visible cell density reduction (13.0-14.0 mm). Susceptibility assays evidenced that E. globulus extract exerted the highest antibacterial activity (MICs = 0.195-0.39 mg/mL), being effective against all the tested strains. Among the phenolic compounds identified in this extract, gallotannins, ellagic acid glycoside, and quercetin derivatives, were the most abundant; and therefore, may exert a positive and contributive effect to the observed antibacterial effect. Overall, the use of plant extracts to control bovine mastitis caused by S. aureus is a promising solution that could contribute to the reduction of the occurrence of dairy food industry contaminations, providing considerable benefits to agro-industries on the formulation of high-quality and safety dairy products.