Evaluation of Antibacterial and Antioxidant Efficacy of the Fern Azolla caroliniana Symbiotic with the Cyanobacterium Anabaena azollae

Abstract

Antibacterial efficacy of the water-fern, Azolla caroliniana Willd., symbiotic with the nitrogen fixing cyanobacterium, Anabaena azollae against seven multidrug resistant pathogenic bacteria were evaluated. Antioxidant and organoleptic properties of the fern were also assessed. Most Gram-negative and Gram-positive bacteria used in this study were highly resistant to 17 antibiotics of aminoglycoside, beta-lactam, cephalosporin and fluoroquinolone groups, as recorded from Kirby-Bauer method. The methanolic extract of A. caroliniana generated 20 mm as the maximum size of zone of inhibition against Staphylococcus aureus, as recorded from the agar-well diffusion method. The minimum inhibitory concentration value, 1.89 mg/ml was due to the methanolic extract against S. aureus and Proteus mirabilis, while the value, 4.27 mg/ml was against Enterococcus sp., Enterobacter aerogenes, Escherichia coli and Pseudomonas aeruginosa. The minimum bactericidal concentration value, 4.27 mg/ml was of the methanolic extract against S. aureus and P. mirabilis, while the value, 21.67 mg/ml was recorded against Citrobacter sp., E. aerogenes, E. coli and P. aeruginosa. Fifty percent inhibition concentration values of free radical scavenging activities of the fern with free radical generating chemicals, 1,1-diphenyl-2-picryl hydrazyl, as well as, 2, 2-azino-bis (ethylbenzthiazoline-6-sulfonic acid), hydrogen peroxide and nitric oxide of the methanolic extract were 8, 10, 10, and 78.8 µg/ml, respectively. In four solvent-extracts with methanol, ethanol, chloroform and n-hexane, several common phytochemicals and phenols were present, while alkaloids and saponins were absent. Processed Azolla was tasteless but not unpalatable. Azolla caroliniana could be used as an antibacterial as well as an antioxidant agent in complementary and alternate medicine.