Bacillus sp. serve as sources for naturally-derived antimicrobial compounds, which can come in the form of either peptides or polyketides. Between these two, peptides, such as surfactins and fengycins, are more abundant than polyketides. These antimicrobial compounds are important for their role in the treatment of infections, as well as in food preservation.
In this study, crude extracts were acquired from BFP011 and subjected to further purification to determine the individual compounds present. This was done using thin-layer chromatography (TLC) and reversed-phase high-performance liquid chromatography (RP-HPLC). The purified fractions revealed the presence of macrolactins and amicoumacins, which are both non-peptides.
Antimicrobial activity of the crude extracts and the purified fractions were determined against Gram-positive and Gram-negative bacteria that are involved in human pathogenesis or food spoilage. Results showed that the compounds were effective against a variety of bacterial species. However, Gram-negative bacteria were observed to be less susceptible to the extracts than Gram-positive bacteria. This difference in sensitivity can be attributed to lower peptidoglycan content in Gram-negative bacteria, since most antimicrobial compounds work by inhibiting peptidoglycan synthesis.
The mechanisms of action of the purified fractions against Salmonella typhi ATCC 5784 were also determined based on changes in bacterial morphology when viewed under a scanning electron microscope. S. typhi was selected for this part of the study because of its ability to cause human disease and survive in low temperature, which could lead to food contamination. Exposure of S. typhi to the purified fractions led to an inhibition of its growth, showing that macrolactins and amicoumacins are sufficient for antimicrobial activity against S. typhi. It was also observed that cells treated with the purified fractions caused deformation of the cell membrane or formation of protrusions on the surface.
Based on these results, the researchers were able to determine that B. licheniformis BFP011 produces non-peptidic antimicrobial compounds, namely macrolactins and amicoumacins. They were also able to observe that these compounds work against various bacterial species and that their mechanism of action involves the destruction of the cell membrane in a time-dependent manner.
“Notably, the scope of potential applications would not be limited to suppressing the bacterial growth in food products, but also include novel antimicrobial therapeutics, which could help to promote human health by lowering the risks associated to infection with multiresistant bacteria,” the researchers concluded. (Related: Antibiotic-resistant bacterial infections continue to rise: Just how inept is the conventional medical industry?)
Aside from naturally-derived antimicrobial compounds, the following natural substances can also protect food from contamination:
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