Antimicrobial potential and seasonality of red algae collected from the southwest coast of India tested against shrimp, human and phytopathogens

Abstract

Fifteen seaweeds belong to 13 families and 6 orders of the rhodophyta were sampled for one year from April 2007 to March 2008 along the southwest coast of India (Indian Ocean). The species were examined for in vitro antimicrobial activity against six pathogenic Vibrio strains isolated from moribund tiger shrimp (Penaeus monodon), six type cultures (Microbial Type Culture Collection, MTCC) of prominent shrimp Vibrio pathogens, 10 multidrug resistant clinical pathogens, four species of Candida obtained from pulmonary TB patients and four species of plant pathogenic fungi to evaluate their potency to be used as natural antibiotics in pharmaceutical and agriculture field. Bioactivity was analyzed from crude extract of fresh and dried samples prepared from different polar and nonpolar solvents. Of these, four species of red algae (Asparagopsis taxiformis, Laurencia ceylanica, Laurencia brandenii, Hypnea valentiae) were found to be highly active. Broadest and highest activity was observed in the crude extract of A. taxiformis. Among the pathogens tested, shrimp pathogenic Vibrios were the most susceptible organisms while phytopathogens were found to be little resistant. In the present study, methanol was found to be the best solvent for extracting antimicrobial metabolites from dried samples rather than fresh. Seasonal variation in the antimicrobial activity was observed with higher level of activity recorded from A. taxiformis between December and January. The active principle of A. taxiformis was purified in column chromatography, TLC and reverse phase HPLC. The individual HPLC peaks were subsequently tested against a panel of pathogenic microorganisms and the active constituent was identi- fied by GC-MS. The antimicrobial profile of A. taxiformis suggested that lipophilic compound which was primarily composed of pyrrole-2-carboxylic acid, pentadecanoic acid and octadecanoic acid might have functional role in the chemical defence against microbial invasion and these compounds could be utilized for the development of medically potential products.