Bioactive Components Identification and Characterization of the Mechanisms of Action of Selected Medicinal Plant Extracts Against Salmonella enterica Serovar Typhi

Abstract

The rise in antimicrobial resistant bacteria has necessitated the search for alternatives therapy, this study evaluates the antimicrobial potency of five medicinal plants against MDR S. Typhi. The leaves of Azadirachta indica, Bambusa vulgaris, Cymbopogon citratus, Moringa oleifera, Carica papaya, were collected, shed-dry, powdered, and soaked in ethanol for 72 hours, dried to generate the crude extract. The potency was tested on MDR S. Typhi isolated from Alheri laboratory. GCMS and Fourier Transform Infrared (FTIR) were performed to identify plant’s active components and functional group(s). Scanning Electron Microscope (SEM) and UV spectrophotometer were used to assay effects on bacterial membrane. MDR S. Typhi was isolated, confirmed through serological and molecular analysis. Both the invA and tviA genes were identified. Azadirachta indica showed the highest activity with a zone of inhibition of 19.6 ± 0.8 mm at 100 mg/mL. The MIC and MBC of A. indica was 50 mg/mL and 100 mg/mL, respectively. GCMS analysis identified cis-13-octadecenoic (19.63%), n-hexadecanoic (17.05%), octadecanoic (6.99%), trans-13-octadecenoic (3.74%) acids, as the major components. FTIR analysis confirmed the presence of hydroxyl, carbonyl, amine, ether, ester, and aromatic functional groups associated with antimicrobial phytochemicals such as phenols, flavonoids, alkaloids, and terpenoids. SEM analysis of treated bacterial cells showed morphological cell deformation. UV spectrophotometric analysis at 260 nm and 280 nm wavelength showed increased absorbance in treated cells, suggesting leakage of nucleic acids and proteins. Azadirachta indica possesses significant antibacterial activity against MDR S. Typhi, primarily through disruption of bacterial membrane integrity and leakage of intracellular contents.