Spectroscopic Analysis and Antibacterial Activity of Partially Purified Dichloromethane Fraction of Emilia praetermissa Milne-Redhead (Asteraceae) Leaf

Purpose The search for better antibacterial agents from plants has resulted in the identification of molecules with existing analogues. Emilia praetermissa is an herbaceous plant that is traditionally used to treat bacterial skin infections and diarrhea. This study aimed to identify compounds in partially purified E. praetermissa and investigate their antibacterial activity. Methods Gradient elution chromatography was used to achieve partial purification of the compounds. Gas chromatography‒mass spectrometry (GCMS) and Fourier transform infrared spectroscopy were used to identify the phytochemicals from the eluent of interest (EP1). The agar well diffusion plate protocol enabled the assessment of the susceptibility profile of the eluents (EP1–EP11) (10 mg/mL) against clinical isolates: Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus . Results EP1 revealed fourteen compounds: 4aS-3,4,5,5,9-tetramethyl-1,25,6,7,8-hexahydro-4a,8-epoxybenzo[7[annulene (15.74%), N-(3-allyl-2-oxo-2,3-dihydro-1,3-b enzothiazol-6-yl) acetamide (5.52%), pentadecane (1.87%), heptacosane (3.52%), heptadecane (1.34%), nonadecane (1.09%), eicosane (3.56%), heneicosane (1.31%), di-sec-butyl phthalate (46.92%), bis(2-ethylhexyl) phthalate (6.62%), 2,4-di-tert-butylphenol (7.90%) and 2-ethyl-2H-benzotriazole (4.51%). The functional groups identified include O-H, N-H, C-H, C-C and C = C, which combine with the data from the GC‒MS. Susceptibility testing revealed the inhibition of Staphylococcus aureus , Bacillus subtilis and Escherichia coli by eluents EP1–EP11, excluding EP4, EP5 and EP10. Conclusion The results show that the identified compounds inhibit the pathogenic bacteria responsible for inducing skin infections and diarrhea, confirming their traditional use.