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.
Keywords: Alkaloids, Antimicrobial, Bacteria, Fungi, Flavoinoids, Saponins, Infectious Diseases, Phytochemicals, Terpenoids, Virus.
