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An antimicrobial activity produced by Bacillus subtilis B38 was found to be effective against several bacteria, including pathogenic and spoilage microorganisms such as, Listeria monocytogenes, Salmonella enteridis, and clinical isolates of methicillin-resistant Staphylococcus species. Nutrients such as carbon, nitrogen sources, and inorganic salts enhanced the production level of the antibacterial activity by B. subtilis B38. A first screening step showed that lactose, ammonium succinate, and manganese most influenced both cell growth and antibacterial activity production. These three factors varied at two levels in eight experiments using full factorial design. Results indicated that maximum cell growth (OD = 10.2) and maximum production of antibacterial activity (360 AU/mL) were obtained in a modified medium containing 1.5% (w/v) lactose, 0.15% (w/v) ammonium succinate, and 0.3 mg/L manganese. Depending on the indicator strain used, the antibacterial activity was 2- to 4-fold higher in the modified culture medium than in TSB medium under the same conditions. Thin layer chromatography-bioautography assay showed the presence of three active spots with R(f) values of 0.47, 0.7, and 0.82 in TSB medium. However, the inhibition zone of two spots (R(f) values of 0.7 and 0.82) was slightly larger in the modified medium. Moreover, a large zone of inhibition with an R(f) value of 0.3, was observed in this modified medium, instead of the spot having an R(f) value of 0.47. These results suggest that the nutrients act as environmental factors, quantitatively and qualitatively affecting the production of antibacterial compounds by B. subtilis B38.

This study investigates the optimal combination of clove, cinnamon, lavender, and myrtle essential oils (EOs) against Escherichia coli. After the GC/MS analyses, the antimicrobial activities of the four EOs were screened. Afterward, a statistical mixture design established the right EOs’ combination capable of protecting milk from E. coli. Results illustrated that the EOs were chemically different and efficient against 14 bacteria. Hence, the simplex‐centroid mixture design was used to build polynomial models describing the relationship between the anti‐E. coli effect and the proportion of each EO. Result depicted that the lowest bacterial survivability was equal to 1.5 × 106·CFU·ml−1 for the combination of cinnamon and lavender; and the combination of cinnamon, lavender, and clove at a concentration of 2 mg/ml. The application of the statistical design concluded that the optimal combination corresponds to 2.4% S. aromaticum, 38.2% L. stoechas, and 59.4% C. zeylanicum. The combination validation exhibited its efficiency as it restricted the E. coli viability to 1 × 106·CFU·ml−1. Practical applications EOs are the new eco‐friendly preservative for food. Their combination (using the right sources and proportions) allows better protection against germs. In this study, the obtained formula may be of interest in the milk and dairy industry as it contributes to protecting milk (and dairy products) against E. coli contamination.

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