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Journal of Biomedicine and Biotechnology
Volume 2012, Article ID 373682, 12 pages
Research Article

Investigation of Antimicrobial Activity and Statistical Optimization of Bacillus subtilis SPB1 Biosurfactant Production in Solid-State Fermentation

1Unité Enzyme et Bioconversion, Ecole Nationale d’Ingénieurs de Sfax, BP W, 3038 Sfax, Tunisia
2Institut Supérieur de Biotechnologie de Sfax, BP 261, 3000 Sfax, Tunisia
3Equipe des Biopesticides, Centre de Biotechnologie de Sfax, BP 1177, 3018 Sfax, Tunisia
4Unité de Bioinformatique, Centre de Biotechnologie de Sfax, BP 1177, 3018 Sfax, Tunisia

Received 13 November 2011; Accepted 20 December 2011

Academic Editor: Guihua H. Bai

Copyright © 2012 Dhouha Ghribi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


During the last years, several applications of biosurfactants with medical purposes have been reported. Biosurfactants are considered relevant molecules for applications in combating many diseases. However, their use is currently extremely limited due to their high cost in relation to that of chemical surfactants. Use of inexpensive substrates can drastically decrease its production cost. Here, twelve solid substrates were screened for the production of Bacillus subtilis SPB1 biosurfactant and the maximum yield was found with millet. A Plackett-Burman design was then used to evaluate the effects of five variables (temperature, moisture, initial pH, inoculum age, and inoculum size). Statistical analyses showed that temperature, inoculum age, and moisture content had significantly positive effect on SPB1 biosurfactant production. Their values were further optimized using a central composite design and a response surface methodology. The optimal conditions of temperature, inoculum age, and moisture content obtained under the conditions of study were 37°C, 14 h, and 88%, respectively. The evaluation of the antimicrobial activity of this compound was carried out against 11 bacteria and 8 fungi. The results demonstrated that this biosurfactant exhibited an important antimicrobial activity against microorganisms with multidrug-resistant profiles. Its activity was very effective against Staphylococcus aureus, Staphylococcus xylosus, Enterococcus faecalis, Klebsiella pneumonia, and so forth.