Antibacterial activity and phytochemical constituents of the aerial parts of Allium sativum L.

Introduction The bulbs of Allium sativum L. (garlic) are widely used as food or condiment, while they have also been used as a famous traditional medicine since ancient times for the treatment of diarrhea, dysentery, pertussis, tuberculosis and scabies, etc. However, most studies have focused on bulbs, and few studies have focused on the abundant aerial parts, which are usually discarded during the harvest season. Methods In this study, Oxford cup and microdilution assays were employed to assess the in vitro antibacterial activity of the aerial parts of A. sativum . The underlying antibacterial mechanism was explored by detecting bacterial biofilm formation, cell wall integrity and intracellular protein leakage. Multiple chromatographic techniques were adopted to isolate and purify chemical components, and the two-fold dilution method was used to screen the antibacterial activity of the obtained compounds. Results To our knowledge, this is the first report investigating the inhibitory effects of the 70% ethanol crude extract from the aerial parts and its fractions (petroleum ether, ethyl acetate, n-butanol, and residual water extracts) against Staphylococcus epidermidis , Staphylococcus aureus , Escherichia coli and Pseudomonas aeruginosa . The results showed that the extracts had different degrees of inhibitory effects on the tested bacteria in vitro , and the ethyl acetate extract had the strongest antibacterial activity. Mechanistic studies suggested that the ethyl acetate extract markedly inhibited biofilm formation of S. epidermidis and S. aureus , increased the permeability of the cell wall and cell membrane, and thereby exerted antibacterial effects. 12 compounds were isolated from the ethyl acetate extract, and their structures were identified by nuclear magnetic resonance (NMR) and mass spectrometry (MS) analysis. In vitro experiments showed that some compounds had noticeable antibacterial activity. Discussion The above results support that the aerial parts of A. sativum are an interesting source of bioactive ingredients, which can be used to prevent and treat bacterial infectious diseases.