Minthostachys verticillata essential oil activates macrophage phagocytosis and modulates the innate immune response in a murine model of Enterococcus faecium mastitis

Minthostachys verticillata essential oil (EO) is a natural product that reports immunomodulatory effects on human T cells as well as anti-inflammatory activity. Bovine mastitis is a worldwide disease, mainly caused by bacteria, affecting milk quality and yield, leading to high economic losses. Environmental pathogens, as Enterococcus faeciurn, are implicated in the disease. Antibiotic therapy is adequate, although it can leave residues in milk, causing problems in human health. The search of immunomodulatory substances for bovine mastitis treatment is a promising alternative strategy. The aim of this study was to characterize the effect of M. verticillata EO on macrophage phagocytosis and evaluate its immunomodulatory and protective effects in mice challenged with E. faecium. The results showed that EO activated macrophage phagocytosis mechanisms inducing reactive oxygen species production. Moreover, EO modulated the innate immune response in mammary glands of female Balb/c mice challenged with E. faecium decreasing the infiltration of polymorphonuclear neutrophils and IL-1 beta and TNF-alpha mRNA expression. In addition, EO increased the expression of IL-10 in the last hours of infection. Treatment with EO did not increase the number of activated CD4(+) or CD8(+) T cells or the production of specific antibodies. These results suggest that EO play an important role in helping to resolve the infection in the first hours without activating adaptive immunity. In addition, a marked decrease of the bacterial count in the glands of mice treated with EO was observed. A natural product such as M. verticillata EO could have a potential use to control bovine mastitis.