Antimicrobial Activity of Selected Plant Extracts against Common Food Borne Pathogenic Bacteria

Increasing antibiotic resistance of important human pathogens calls for investigation and discovery of new antibiotics. Various medicinal plants and spices available in Fiji have antimicrobial potential against various food-borne pathogens. This research aims to address the assumed antimicrobial activity of twelve selected plant extracts against fifteen food-borne pathogens and to evaluate the pathogens resistances. The Kirby-Bauer Method was used in this study to determine the potency of plant extracts. Total Phenolic Content (TPC) was determined by the Folin-Ciocalteu Spectrophotometric method. The chosen plant species samples used were Morinda citrifolia (noni) leaves, Syzygium aromaticum (clove) bud, Psidium guajava (guava) leaves, Ocimum basilicum (basil) leaves, Carica papaya (pawpaw) leaves, Azadirachta indica (neem) seed oil, Citrus limon (lemon) leaves, and Zingiber officinale (ginger) root. Extracts from these eight plants were tested against common food-borne bacteria; Clostridium perfringens, Citrobacter youngae, Enterobacter aerogenes, Enterobacter amnigenus, Enterobacter cloacae, Escherichia coli, Hafnia alveia, Klebsiella oxytoca, Klebsiella pneumoniae, Morganella morganii, Proteus vulgaris, Proteus mirabilis, Photobacterium damselae, Raoultella ornithinolytica and Vibrio alginolyticus. Both resistance and antibacterial responses were observed for the different plant extracts. All plant extracts were successful in inhibiting bacterial growth for different number of species at varying levels of effectiveness with noni being the most effective. The highest inhibition zones (ZOI>14 mm) were shown by garlic, basil, jasmine and neem. Highest mean ZOI was shown by noni at 11.4 mm followed by garlic at 10.1 mm and clove at 8.4 mm. Minimum inhibitory concentrations were determined for extracts exhibiting antibacterial potential. TPC may attribute to the antibacterial properties of the extracts, however, this needs further investigation. Results indicate presence of possible bioactive compounds in the extracts which can aid in search for new antibiotic drugs from plant sources. Studies that identify the compounds of therapeutically important flora in Fiji is recommended.