Anti-shigellosis Activity and Mechanisms of Action of Extracts from Diospyros gilletii Stem Bark.

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Abstract
Shigellosis is a pathological condition that affects the digestive system to possibly cause diarrhoea. Shigella species, which are responsible for this disease, are highly contagious and spread through contaminated food and water. The increasing development of resistance by Shigella species necessitate the urgent need to search for new therapies against shigellosis causing diarrhoea. The scientific validation of medicinal plants, such as Diospyros gilletii, which is used for the traditional treatment of diarrhoeal conditions is worthwhile. The present study aims to investigate the antibacterial activity of extracts from D. gilletii against selected Shigella species. Extracts from D. gilletii stem bark were prepared by maceration using various solvents. An-tibacterial activity of D. gilletii extracts was evaluated on Shigella dysenteriae, S. flexneri, S. boydii, and S. sonnei using a microdilution method, whereas cytotoxicity test was performed on Vero and Raw cells using resazurin-based colorimetric assay. Bacterial membrane permeability studies were evaluated using pro-pidium iodide (PI) and 1-N-phenylnaphthylamine (NPN) uptake assays, whereas inhibition and eradica-tion tests on bacterial biofilms were carried out by spectrophotometry. As a result, methanol, ethanol and hydroethanol extracts of D. gilletii inhibited the growth of S. boydii, S. flexneri and S. sonnei with MIC values ranging from 125 to 500 µg/mL, without toxicity to Vero and Raw cells. Time kill kinetics revealed bacteri-cidal orientation at 2MIC and 4MIC, and bacteriostatic outcome at 1/2MIC. The mechanistic basis of anti-bacterial action revealed that D. gilletii extracts inhibited and eradicated Shigella biofilms, and promoted the accumulation of NPN and PI within the inner and outer membrane of bacteria to increase membrane per-meability, thereby causing membrane damage. This novel contribution toward the antibacterial and mech-anisms of action of D. gilletii extracts against Shigella species substantiate the use of this plant in the tradi-tional treatment of infectious diarrhoea.