The use and search for new medicines and dietary supplements derived from plants have enhanced in the modern era. Plants are rich in a wide variety of secondary metabolites, such as tannins, terpenoids, alkaloids, and flavonoids, which have been found in vitro to have antimicrobial properties. Polyphenols are natural compounds characterized by a high structural variety, and their existence in plants makes them essential components. Increasingly, resistant bacteria require the continuous need for new and effective antibiotics. This class of natural products is becoming the target of anti-infective research, and many groups have identified that phenolic compounds are possessing broad-spectrum antibacterial and antiviral activity. Owing to interest in their biological activities, both the chemical structure of the phenolic moiety and any attached chemical groups define whether the polyphenol is bioactive or not. Compared to other phenolics, flavonoids class have been abundantly used in anti-infective research.
This chapter summarizes the application of polyphenol tested by various groups against infectious diseases caused by bacteria and viruses as pathogens. The reported MIC values are presented in a concise table, which is conflicting among different groups, possibly due to assay parameters and strain variation. However, it is shown that phenolic compounds have great potentials, which requires future research for the development of novel antimicrobial or antiviral agents or aid as a synergistic agent in combination with conventional anti-infective drugs.