Plant antimicrobial agents and their effects on plant and human pathogens

Abstract

To protect themselves, plants accumulate an armoury of antimicrobial secondary metabolites. Some metabolites represent constitutive chemical barriers to microbial attack (phytoanticipins) and others inducible antimicrobials (phytoalexins). They are extensively studied as promising plant and human disease-controlling agents. This review discusses the bioactivity of several phytoalexins and phytoanticipins defending plants against fungal and bacterial aggressors and those with antibacterial activities against pathogens affecting humans such as Pseudomonas aeruginosa and Staphylococcus aureus involved in respiratory infections of cystic fibrosis patients. The utility of plant products as "antibiotic potentiators" and "virulence attenuators" is also described as well as some biotechnological applications in phytoprotection.

Keywords: antimicrobial; cystic fibrosis; infectious disease; phytoalexin; phytoanticipin; phytoprotection; secondary metabolites.

Figure 1.

Examples of antimicrobial phytoalexin structures. (A) Scopoletin from tobacco, (B) camalexin from A. Thaliana, (C) sakuranetin, (D) nomilactone B from rice, and (E) glucosinolates from Brassicacea. Structures of the R groups of indol-3-ylmethyl (E, left) and 4-methylsulfinylbutyl glucosinolate (E, right) are shown as examples of Arabidopsis tryptophan- and methionine-derived glucosinolates, respectively.

Figure 2.

Examples of antimicrobial phytoanticipin structures. (A) The major oat root saponin avenacin A-1, and (B) the saponin α-tomatine from tomato. Tomatidine is the aglycon version of the phytoanticipin tomatine.

Figure 3.

Some examples of plant products defined as “antibiotic potentiators” (A) or “virulence attenuators” (B) could allow the current conventional arsenal of antibiotics to gain back some of the therapeutic applications lost from the spread of MDR and others could assist the host immune system to adequately respond to the pathogen invasion. 5’-MHC, 5’-methoxyhydnocarpin.