Antimicrobial defenses of Caulerpa mexicana and Udotea looensis against Vibrio spp. and Bacillus sp.

Abstract

In a broad survey of extracts of common marine algae from the Florida Keys against an extensive panel of environmental bacteria, extracts from the green algae Caulerpa mexicana and Udotea looensis exhibited significant activity against two conspecific strains of Vibrio sp. from Florida and one strain of Bacillus sp. from the Red Sea. To continue the investigation of antibacterial defenses of marine algae, crude extracts from C. mexicana and U. looensis were subjected to bioassay-guided fractionation. Extracts were partitioned between ethyl acetate and DI water. The non-polar fractions were separated using Si gel medium pressure liquid chromatography followed by reverse phase high pressure liquid chromatography. Bacterial cultures were maintained on A1 media. Extracts were dissolved in DMSO (600 µg/ml ≤ natural volumetric concentration) and added to each well of a 96-well plate using DMSO (solvent), streptomycin and tetracycline (positive) as controls. Initial and final readings were obtained on a Biotech plate reader at 625nm. C. mexicana and U. looensis produce metabolites that selectively inhibit the growth of one strain of Vibrio sp. or Bacillus sp. and several others that show broad spectrum antimicrobial activity against potential pathogens in the marine environment. This study was conducted by PharmD candidates as part of a college wide research training program at Chicago State University.