In vitro antimicrobial activity of the aqueous extract and essential oil of rosemary (Rosmarinus officinalis L.) and clove (Caryophyllus aromaticus L.) against strains of Staphylococcus aureus and Escherichia coli

Abstract

Staphylococcus aureus and Escherichia coli have virulence factors that provide them with high adaptability, culminating in their ever-increasing antimicrobial resistance, which in turn is worsened by the indiscriminate and incorrect use of antibiotics. Therefore, the search for new compounds to be used in an effective antimicrobial therapy is essential, and in that context medicinal plants are promising alternatives for such purpose. We evaluated the in vitro antimicrobial activity of the aqueous extract and essential oil of Rosmarinus officinalis L. (rosemary) and Caryophyllus aromaticus L. (clove) against standard strains of S. aureus and E. coli. Clove essential oil has antimicrobial activity against both analyzed strains, when analyzed by both disc diffusion and well diffusion methods, at the evaluated concentrations. Rosemary essential oil showed growth-inhibitory activity on the E. coli strain by all methods used, but it showed activity against S. aureus only by the well diffusion method. On the other hand, extracts of neither plants inhibited growth of the bacterial strains. We concluded that both clove and rosemary essential oils have in vitro antimicrobial activity, whereas their aqueous extracts show no growth-inhibitory activity. To our knowledge, this is the first report of the effects of clove aqueous extract on bacterial strains.