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

Shin, Bora; Park, Woojun

Reportedly, terpenoids have exhibited cancer preventive effects and cytotoxic effects on tumor cells in preclinical animal models (41) . Monoterpenes, such as palmarosa oil, cinnamon oil, geraniol, carvacrol, eugenol, and thymol, are present in aromatic plants, fruits, vegetables, and herbs (60) . Essential oils, which are terpenoids, are powerful antioxidants effective at scavenging free radicals. Palmarosa oil from Cymbopogon martinii is primarily used in skin care and treatment of throat infection and has also demonstrated the highest antimicrobial activity against S. aureus and Escherichia coli (42) . In one study, a checkerboard assay revealed synergistic effect of cinnamon oil with other antimicrobial agents, such as chlorhexidine, triclosan, and gentamicin (61) . Cinnamon oil exhibits antimicrobial activity on both planktonic and attached cells of clinically isolated S. epidermidis and S. aureus strains (62) . Interestingly, cinnamon oil has been shown to increase the effectiveness of gentamicin and chlorhexidine as well as the ability to detach and kill S. epidermidis biofilms (61, 62) . Geraniol from Pelargonium graveolens is used as a flavoring agent and stimulant (63) and exhibits significant growthinhibitory effects against S. aureus, Bacillus subtilis, Klebsiella pneumoniae, and E. coli (43) . The phenolic monoterpenes carvacrol and thymol are major components of the essential oils of Origanum and Thymus species (64) . Carvacrol and thymol have been extensively tested as antimicrobial compounds against pathogens, including B. cereus, E. coli O157:H7, Enterococcus faecalis, Listeria monocytogenes, Sa. typhimurium, S. aureus, Pseudomonas fluorescens, and Vibrio cholerae (43, 64) . In one study, the live/dead assay of Streptococcus pyogenes demonstrated dead cells 1 h after the incubation of live cells with carvacrol (43) . Eugenol and isoeugenol are components of essential oils and are widely studied. They showed synergistic effect with most antibiotics against E. coli, E. aerogenes, P. vulgaris, P. aeruginosa and S. typhimurium, among which the most obvious are ampicillin, polymyxin B, norfloxacin, tetracycline, rifampicin, and vancomycin (64, 65) .