Antimicrobial Activity of Natural Extracts: The Problem of Mathematical Modeling

The antimicrobial activity of plants, algae, and derived extracts has been a subject of interest for the scientific community. Algae extracts have demonstrated their potential as a source of natural antimicrobial agents. Because of their antibacterial capacity and low toxicity, algae extracts have been studied as natural preservatives in food and cosmetic formulations. The use of these extracts has the potential to minimize the use of synthetic preservatives, which may be harmful to both human health and the environment. Nonetheless, the use of end-point techniques to calculate the minimal inhibitory concentration instead of creating growth inhibition curves usually leads to an absence of mathematical modeling procedures on the bacterial inhibition behavior of natural extracts. The goal of mathematical modeling is to describe the relationship between the concentration of an inhibitory agent (such as a drug or a toxin) and the growth rate of a population. For this purpose, the data obtained during the growth of six different bacteria in the presence of different concentrations of Ascophyllum nodosum (L.) extracts were recorded over 24 h. Later, the collected data were modeled based on different classical sigmoidal models, e.g., Weibull, logistic, and Gompertz, that were applied to define the critical growth phases and infer the kinetic parameters. The obtained parameters led to the conclusion that the inhibition mechanisms behind the antibacterial effects of the algae extracts are diverse towards different microorganisms. The presence of the extract led to a diminution of the specific growth velocity in some cases such as Staphylococcus epidermidis while in the replication of other bacteria such as Bacillus cereus, the extension of the lag phase was the predominant inhibition mechanism.