ANTIMICROBIAL ACTIVITY OF EXTRACTS FROM SELECTED SOUTHERN AFRICAN MARINE MACROALGAE

Extracts from 56 southern African seaweeds, from the Divisions Chlorop hyta (green), Phaeophyta (brown) and Rhodophyta (red), were screened a gainst 12 bacteria, two yeasts and two moulds for antimicrobial activi ty. Seaweed extracts were prepared by boiling powdered samples in 80% ethanol. Extracts were pipetted into wells in overlay agar plates seed ed with the test microorganisms. Generally, the bacteria were more sus ceptible to the antimicrobial effects of seaweed extracts than the yea sts and moulds. Of the test strains, more Gram-positive than Gram-nega tive bacteria were inhibited by the extracts, with Bacillus subtilis b eing the most susceptible. The extracts from the Phaeophyta (brown alg ae) exhibited the largest relative activity, against all the test stra ins. Of the seaweeds tested here, the brown alga Zonaria subarticulata (Lamouroux) Papenfuss showed the highest amount and broadest spectrum of antimicrobial activity against the microorganisms tested in this s tudy.