Herbal Medicine: Traditional Approach to Treat Infections

Infectious diseases are a major cause of morbidity and mortality at a worldwide level. While common cold, encephalitis, meningitis and gastroenteritis are mostly triggered by viruses, cholera, diphtheria, dysentery, tuberculosis, typhoid and pneumonia infections are caused by various bacteria, whereas valley fever, histoplasmosis, candidiasis, ringworm and eye infections are generated by several fungi. Also, ectoparasites like mites, lice, ticks and fleas can be responsible for some infections by attaching to the skin. However, after the onset of COVID-19, which mostly presents as a respiratory disease, a top interest has been put on virus research. Many studies have shown that phytochemicals exert a plethora of biological effects, among them, their antimicrobial action through different mechanisms has been highly underlined. Indeed, they are able to damage the bacterial cell membrane and suppress diverse virulence factors, including inhibition of the activity of various enzymes and toxins and biofilm formation. This chapter summarizes the impact of certain phytochemicals, for example, flavonoids, polyphenols, saponins, steroids, tannins, terpenoids, and alkaloids, as naturally-occurring bioactive compounds present in plants, in several infectious diseases.

Some herbal medicines containing flavonoids form complexes with cell walls of bacteria, protein and extracellular components and are important and effective antimicrobial compounds. Herbal medicines contain terpenoids involved in weakening microorganism cell wall and membranous tissue dissolution, thus inhibiting the growth of infections. Saponins found in herbal medicines cause microbes enzyme leakage from the cell, whereas Steroid in antimicrobial drugs is responsible for liposome leakage from the lipid bilayer membrane. Based on the evidences, the antimicrobial activity of the medicinal plant Veronica biloba was found against E.coli, S.aureus, and Aspergillus fumigatus pathogens. The common herbs tarragon and thyme both contain caffeic acid, which is effective against viruses, bacteria, and fungi. Organosulphur compounds such as allicin, isothiocynate and ajoene have shown antibacterial activity against both gram-positive and gram-negative bacteria. Catechins, the most reduced form of the C3 unit in flavonoid compounds, deserve special mention due to their occurrence in green teas. It was noticed that teas also exerted antimicrobial activity against Vibrio cholerae, S. mutans, shigella and other microorganisms. This chapter focuses on all aspects of infectious diseases and herbal medicines, including chemical constituents and their therapeutic effects.