The antimicrobial activity of an aqueous extract of Brassica negra

An aqueous extract from the seeds of Brassica negra was shown to be effective in reducing the numbers of viable planktonic and sessile cells of a Pseudomonas sp., the fungus Aspergillus fumigatus and a mixed sulphate-reducing bacteria (SRB) culture, all isolated from contaminated diesel oil. The most resistant organism in the planktonic state was A. fumigatus, which required 24 h treatment with 0.04% mustard seed to reduce the cell numbers to below the detection level of 10 cells/ml. In the sessile state SRB were the most resistant, their numbers being reduced significantly only after 1 h treatment with 0.25% mustard seed. Planktonic Pseudomonas sp. and SRB were undetectable after 24 h contact time with 0.01%. Sessile Pseudomonas and A. fumigatus cell numbers were substantially reduced after 1 hoursʹ contact with 0.05%. These results show that the natural biocide, like other antibiotics and synthetic antimicrobial agents, is less effective against sessile than planktonic cells; nevertheless this aqueous extract of Brassica negra seeds has potential for use against microorganisms in industrial biofilms.