Antimicrobial efficacy of select medicinal plant extracts from Bangladesh against food-borne bacterial pathogens

We assessed the antimicrobial activity of extracts prepared with four solvents (hexane, acetone, ethanol, water) from 45 medicinal plants used in Bangladesh. Food pathogenic bacteria (Gram-positive: Bacillus cereus, Listeria innocua, Streptococcus faecalis, and Gram-negative: Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica, and Shigella sonnei) were tested using a broth microdilution method. The extraction yield was highest (26%) for the water extract of Carica papaya and lowest (0.4%) for the acetone extract of Cynodon dactylon. In general, acetone extracts exhibited much more antibacterial activity than those obtained with the other three solvents (hexane, ethanol, and water). Gram-positive bacteria were more sensitive than Gram-negatives. Streptococcus faecalis was the most susceptible to inhibition by examined extracts, whereas E. coli and P. aeruginosa were the most resistant. Most inhibitory concentration-50 (IC₅₀) values ranged between 101 and 500 μg/mL (64 extracts, 35.5%), followed by the range of 501–1000 μg/mL (40 extracts, 22.2%). Based on IC₅₀, the most effective plants were three species of Piper (Piper nigrum, Piper betle, and Piper chaba), followed by Nigella sativa, Psidium guajava, Syzygium cumini, C. dactylon, and Phyllanthus emblica. In addition, the toxicity of chosen extracts against normal and malignant cell lines was tested; the most effective extracts were toxic against the human lung carcinoma cell line A549, but less toxic against the human Caucasian foetal lung cell line WI26VA4. These findings suggest that some plant extracts could be employed to treat food-borne bacterial infections, or as herbal preservatives in the food sector.