Tannins as an alternative to antibiotics

Excessive use of antibiotics has led to the emergence of multidrug-resistant bacteria that are a serious threat to human health. There is a need to develop efficient antibacterial agents to address this problem. Tannins are high molecular weight (MW) polyphenols (500−30,000 Da), distributed throughout the plant kingdom. Tannins are one of the major compounds in plants with potential health benefits. This review addresses the antibacterial and antivirulence effects of different types of tannins and highlights the underlying antibacterial mechanisms of action. Furthermore, an overview of the antibacterial effects of emerging tannin-loaded nanoparticles/hydrogels is presented. Tannins have been found to inhibit bacterial growth using different mechanisms of action including iron chelation, inhibition of cell wall synthesis, disruption of the cell membrane, and inhibition of fatty acid biosynthetic pathways. Tannins can act as quorum sensing inhibitors and attenuate the gene expression of several virulence factors such as biofilms, enzymes, adhesins, motility, and toxins. Also, tannin-loaded nanoparticles/hydrogels show good antibacterial effects. Overall, tannins may be promising antibacterial and antivirulence agents for preventing bacterial infections.