Zoonotic Diseases and Phytochemical Medicines for Microbial Infections in Veterinary Science: Current State and Future Perspective

Shin, Bora; Park, Woojun

Antimycobacterial activity of andrographolide, a natural diterpenoid, has been demonstrated using luciferase reporter (51) (52) (53) 57) phage assay (66) , confirming that andrographolide exhibits antimicrobial activity by targeting the aminoglycoside 2 ′ -N-acetyltransferase in Mycobacterium tuberculosis (66) . It is widely used in traditional Chinese medicine and shows a wide range of biological effects, including anti-cancer and anti-inflammatory effects (44) . In addition, it exhibits weak antimicrobial activity against S. aureus and B. subtilis. The specific antimicrobial mechanisms of most phytochemicals are not known; however, triterpenes, including oleanolic and ursolic acids, have been shown to exhibit antibacterial activity as adjuvants of aminoglycoside by changing membrane permeability and proton-motive force against Acinetobacter baumannii (9) . Other triterpenoids, such as betulinic acid, rotundic acid, and amyrin, have shown anti-staphylococcal activities. Although antibacterial effects of phytochemicals are generally weaker than those of antibiotics, phytochemicals can be synergistically used with antibiotics to develop different antibacterial mechanisms or pathways to produce antimicrobial effects against S. aureus, B. cereus, and P. aeruginosa (46, 47, 66) . Astaxanthin, a tetraterpene, is an antioxidant with antiinflammatory properties; therefore, it is used as a therapeutic agent in atherosclerotic cardiovascular disease (48) . In addition, carotenoids are lipid-based antioxidants in the diet that have demonstrated both anti-inflammatory and antibacterial effects (49) . The antioxidative effects of phytochemicals have been more widely reported than the antimicrobial activity of triterpenes and sesquiterpenes (41, 46) . Phenolics are secondary metabolites of plants containing one or more hydroxy derivatives of benzene rings and are generally involved in defense against ultraviolet radiation or attacks by pathogens in plants. They are widely distributed in plants and have demonstrated antimicrobial properties (6, 53) . For example, there is a wide range of phenolic compounds in bilberry, cranberry, and blueberry, such as anthocyanidins, delphinidin, flavone, luteolin, flavonols, myricetin, quercetin, rutin, and (-)-epigallocatechin-3-gallate (50, 52) . Only a few studies have examined the antibacterial properties of anthocyanins. Anthocyanins and cyanidins have been shown to inhibit the growth of E. coli (51) . Although flavonoids have a very broad spectrum of pharmacological activities, their mode of action is only partially understood. 3-p-Trans-coumaroyl-2hydroxyquinic acid (CHQA) has shown notable antioxidant activity and antimicrobial activity against S. aureus (67). CHQA contains 2-hydroxyquinic acid moiety together with a pcoumaric acid, but it is unclear which moiety or group of this phytochemical is the critically active factor for its antibacterial activity (67) . p-Coumaric acid shows antibacterial activity against E. coli by destroying cell membranes and binding to the bacterial genomic DNA to inhibit cellular functions (68) .