Antibacterial Activity of Different Solvent Leaf Extracts of Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae): An Invasive Alien Medicinal Plant in South Africa

Abstract

Background and Aims: Antimicrobial resistance (AMR) has emerged as a major global public health concern, significantly reducing the efficacy of conventional antibiotics and complicating the treatment of infectious diseases. The rapid emergence and dissemination of resistant microbial strains have intensified the search for novel antimicrobial agents from natural sources. Medicinal plants have continued to attract considerable scientific interest owing to their rich repository of bioactive secondary metabolites. Tithonia diversifolia (Hemsl.) A. Gray, an invasive plant species widely distributed across Africa, is extensively employed in traditional medicine for the treatment of various ailments, suggesting the presence of pharmacologically active compounds. This study evaluated the in vitro antibacterial activity of different solvent leaf extracts of T. diversifolia using solvents of varying polarity. Study Design: To evaluate the in vitro antibacterial activity of T. diversifolia leaves using solvents of varying polarity. Place and Duration of Study: Fresh plant materials of T. diversifolia were collected from wild growing plants along Main Road, Vulindlela, off University of Zululand, KwaDlangezwa, KwaZulu-Natal, South Africa. Methodology: Sequential extraction of powdered air-dried leaves of T. diversifolia was carried out using n-hexane, chloroform, ethyl acetate, and methanol. Antibacterial activity of the extracts was evaluated against selected Gram-positive and Gram-negative bacterial strains using agar disc diffusion and broth microdilution techniques. Ciprofloxacin and gentamycin were used as standard reference antibiotics. Zones of inhibition (IZ) and minimum inhibitory concentrations (MICs) were determined for all extracts. Results: All solvent extracts demonstrated varying degrees of antibacterial activity against the tested bacterial strains. The ethyl acetate extract exhibited the strongest antibacterial activity, producing inhibition zones ranging from 10.03 ± 0.3 to 20.70 ± 0.8 mm and MIC values between 0.6 and 5.0 µg/mL. The hexane extract also showed pronounced antibacterial effects with comparable inhibition zones and MIC ranges. In contrast, methanol and chloroform extracts exhibited moderate to weak antibacterial activities. Overall, Gram-positive bacteria were more susceptible to the extracts than Gram-negative bacteria, possibly due to structural differences in their cell walls. The superior activity observed in the ethyl acetate fraction suggests that moderately polar solvents were more effective in extracting bioactive antibacterial phytoconstituents from T. diversifolia. These findings are consistent with previous reports indicating that solvent polarity significantly influences phytochemical recovery and biological activity. Conclusion: The findings of this study demonstrate that different solvent leaf extracts of Tithonia diversifolia possess significant in vitro antibacterial activity, particularly the ethyl acetate and hexane fractions. The enhanced activity observed in moderately polar solvent extracts suggests the presence of potent bioactive phytochemicals with broad-spectrum antibacterial potential. These results support the ethnomedicinal use of T. diversifolia and highlight its potential as a promising source of novel antibacterial agents. Further phytochemical isolation, purification, and characterization studies are recommended to identify the active compounds responsible for the observed antibacterial effects and to explore their potential application in antimicrobial drug development.