AUTHOR=Gonelimali Faraja D. , Lin Jiheng , Miao Wenhua , Xuan Jinghu , Charles Fedrick , Chen Meiling , Hatab Shaimaa R. 

TITLE=Antimicrobial Properties and Mechanism of Action of Some Plant Extracts Against Food Pathogens and Spoilage Microorganisms

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01639

DOI=10.3389/fmicb.2018.01639

ISSN=1664-302X

ABSTRACT=<p>This work aims to evaluate the antimicrobial potential of ethanolic and water extracts of roselle (<italic>Hibiscus sabdariffa)</italic>, rosemary (<italic>Rosmarinus officinalis)</italic>, clove (<italic>Syzygium aromaticum</italic>), and thyme (<italic>Thymus vulgaris</italic>) on some food pathogens and spoilage microorganisms. Agar well diffusion method has been used to determine the antimicrobial activities and minimum inhibitory concentrations (MIC) of different plant extracts against Gram-positive bacteria (<italic>Bacillus cereus, Staphylococcus aureus</italic>), Gram-negative bacteria (<italic>Escherichia coli, Salmonella enteritidis, Vibrio parahaemolyticus</italic>, and <italic>Pseudomonas aeruginosa</italic>), and one fungus (<italic>Candida albicans</italic>). The extracts exhibited both antibacterial and antifungal activities against tested microorganisms. Ethanolic roselle extract showed significant antibacterial activity (<italic>P</italic> &lt; 0.05) against all tested bacterial strains, while no inhibitory effect on <italic>Candida albicans</italic> (CA) was observed. Only the ethanolic extracts of clove and thyme showed antifungal effects against CA with inhibition zones ranging from 25.2 ± 1.4 to 15.8 ± 1.2 mm, respectively. <italic>Bacillus cereus</italic> (BC) appears to be the most sensitive strain to the aqueous extract of clove with a MIC of 0.315%. To enhance our understanding of antimicrobial activity mechanism of plant extracts, the changes in internal pH (pH<sub>int</sub>), and membrane potential were measured in <italic>Staphylococcus aureus</italic> (SA) and <italic>Escherichia coli</italic> (EC) cells after exposure to the plant extracts. The results indicated that the plant extracts significantly affected the cell membrane of Gram-positive and Gram-negative bacteria, as demonstrated by the decline in pH<sub>int</sub> as well as cell membrane hyperpolarization. In conclusion, plant extracts are of great value as natural antimicrobials and can use safely as food preservatives.</p>