Essential Oils, Polyphenols and Glycosides: Secondary Plant Metabolites against Human Pathogenic Microbes

Higher plants produce secondary metabolites involved in defense mechanisms against herbivores, pests and pathogens. These phytochemicals have also potential healthy properties on human organism, including antioxidant, antiinflammatory and anti-microbial. The pressure to discover and develop new and effective anti-infectious substances has grown due to the intensification of new and reemerging infectious diseases as well as the increasing resistance to the antibiotics in current clinical use. There are several approaches to control diseases caused by microorganisms, and one of them is the use of natural bioactive chemicals that can combat the infection. The essential oils, polyphenols and glycosidic glucosinolates extracted from various species (e.g. medicinal and aromatic plants) have shown promising anti-microbial activity against several pathogens responsible for human diseases. Some of these diseases include mouth diseases as periodontitis, urinary infections, acne, stomach cancer and ulcers associated with Helicobacter pylori, wound infections and gastric infections. Beyond the in vitro and in vivo studies, several compounds from the plant secondary metabolites have been subjected to clinical trials in order to validate their efficacy as anti-infectives (e.g. proanthocyanidins, a polyphenol, that have been tested against periodontitis or tea tree oil 4% against methicillin-resistant Staphylococcus aureus – MRSA) for future prescription. As most of these compounds have poor water solubility and are easily oxidized a chemical transformation which may alter their anti-infective properties, new strategies are being considered both to protect these phytochemicals against oxidation and to enhance their bioavailability and delivery to the desired organs. This chapter summarizes and discuss the most promising phytochemicals that are being used to treat human diseases, antimicrobial mechanisms, the results of clinical trials and the new approaches based on nanoencapsulation strategies to deliver and target these compounds in vivo.

Keywords: Anti-infective properties, Bioavailability, Clinical trials, Essential oils, Glucosinolates, In vivo anti-microbial activity, Nanoencapsulation, Phenolic acids, Polyphenols, Proanthocyanidins.