Antibacterial activity of the terrestrial fern Lygodium flexuosum (L.) Sw. against multidrug resistant enteric- and uro-pathogenic bacteria

Abstract

Objective: To investigate antibacterial properties of the terrestrial fern Lygodium flexuosum (L. flexuosum) obtained from Kalahandi district, Odisha against enteric- and uro-pathogenic bacteria isolated from clinical samples. Methods: Frond-extracts of L. flexuosum were obtained by the cold percolation method using four solvents, petroleum ether, chloroform, methanol and water. Antibacterial potencies of concentrated cold frond-extracts were tested by the agar-well diffusion method against 7 multidrug resistant (MDR) bacteria of which, 2 were Gram-positives, methicillin resistant Staphylococcus aureus (MRSA) and vancomycin resistant Enterococcus faecalis (VRE), and 5 Gram-negatives, Enterobacter aerogenes, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Proteus mirabilis. Results: The cold-water frond-extract had the best antimicrobial activity against 7 MDR bacterial isolates, compared to extracts with other solvents. Values of zones of inhibition against MRSA and P. mirabilis were the highest, 29 mm. Zones of inhibition against VRE and P. aeruginosa were 25 mm, while those were 23 mm against E. aerogenes and E. coli. The least size of zone of inhibition 19 mm was recorded against K. pneumoniae. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of active frond-extracts with water, chloroform, methanol, and petroleum ether were recorded. For the water extract, the MIC value 1.562 mg/mL against MRSA and P. mirabilis, but the value 3.25 mg/mL against VRE, E. aerogenes and P. aeruginosa, while the value of 12.5 mg/mL against K. pneumoniae were recorded. MBC values were the least with chloroform-extracts, with the range 12.5 for 6 bacteria, excluding P. aeruginosa for which, the value 25 mg/mL was recorded as MBC. Conclusions: Phytochemical analysis of the water-extract of L. flexuosum confirmed the presence of glycosides and carbohydrates, but alkaloids, terpenoids, steroids, saponins, tannins, and flavonoids were absent. L. flexuosum, being a fern, is a suitable non-microbial source of antimicrobial for MDR strains of major enteric and uro-pathogens.

Keywords

• Lygodium flexuosum
• Terrestrial fern
• Multidrug resistant bacteria
• Phytochemical analysis
• Enteric- and uro-pathogenic bacteria