Synergistic Efficacy of Lichen Extracts and Silver Nanoparticles Against Bacteria Causing Food Poisoning

Lichens and lichen products have been used in traditional medicines for centuries. Silver has been used in many applications because it possesses several activities including antimicrobial activity. The objective of the investigation was to evaluate synergistic antibacterial effect of extracts of Parmotrema pseudotinctorum (des. Abb.) Hale and Ramalina hossei H. Magn and G. Awasthi and silver nanoparticles, if any, against bacteria causing food poisoning. The silver nanoparticles were prepared by chemical reduction method employing silver nitrate. The extracts of selected powdered lichen materials were obtained using methanol solvent. To evaluate the antibacterial efficacy of the lichen extracts and nanoparticles alone and in combination against Gram positive and Gram negative test bacteria, Agar well diffusion method was employed. The lichen extracts were more effective against Gram positive bacteria while silver nanoparticle on Gram negative bacteria. Among lichen extracts, R. hossei was found to affect bacteria to more extent than P. pseudotinctorum. In combination trails, the result was found to be superior to that of individual treatment. Gram negative bacteria were found to be more sensitive in combination trails as compared to extract alone. In case of combination trials involving R. hossei, the inhibition of E. coli and S. typhi was higher than that of standard antibiotic. The variation in sensitivity of test bacteria to single and combined treatment is possibly due to the nature of cell wall. It was found that the extracts and silver nanoparticles have synergistic action against test bacteria. Further experiments are to be conducted to isolate the active principle from extract and to evaluate the in vivo potential of extracts singly and in combination with silver nanoparticles.