Antibacterial potency and synergistic effect of certain plant extracts against food-borne diarrheagenic bacteria

Abstract

In the present study, aqueous and ethanolic extracts of leaves of six commonly available medicinal plants, Balanites aegyptiaca (L.) Del. (Balanitaceae), Hyptis sauveolens Poit. (Lamiaceae), Lawsonia inermis L. (Lathyraceae), Leucas aspera L. (Lamiaceae), Lobelia nicotianaefolia Roth. ex. Roem. & Schult. (Lobeliaceae) and Phyllanthus madraspatana L. (Euphorbiaceae), individually and in combinations were tested in crude form for their antibacterial activity against five different diarrheagenic bacteria, Bacillus cereus, Staphylococcus aureus, Escherichia coli O157:H7 (enterohemorrhagic E. coli, EHEC), Salmonella enteritidis and Listeria monocytogenes. Cifroflaxacine (20 μg) was used as antimicrobial standard. The highest antimicrobial activity was recorded in both crude aqueous leaf extract (CALE) and crude ethanolic leaf extract (CELE) of L. nicotianaefolia when all the extracts were tested individually. The zone of inhibition (IZ) of 2.2 cm against S. aureus and S. enteritidis, 2.3 cm against B. cereus and L. monocytogenes were observed in CELE of L. nicotianaefolia. CALE and CELE of H. sauveolens and P. madraspatana when tested individually showed least IZ against test organisms (IZ, 0-1.2 cm). Synergistic activity of CALE and CELE of selected plant leaves, in combination of two, three, four, five and six against test organisms ranged from 0-2.8 cm zone of inhibition. The highest IZ of 2.8 cm was observed against S. aureus in CELE combination of B. aegyptiaca + L. nicotianaefolia. The IZ range of 2.6-2.8 was recorded for standard antibiotic, ciprofloxacin against test organisms. The combined or synergistic activity of CALE and of CELE also showed closer IZ to that of standard antibiotic, against food-borne diarrheagenic bacteria, there is a scope to develop effective combination of antimicrobial agents in purified form. _____________________________________________________________________________________________________________