Antibacterial Activities of Crude Secondary Metabolite Extracts from Pantoea Species Obtained from the Stem of Solanum mauritianum and Their Effects on Two Cancer Cell Lines

Endophytes are microorganisms that are perceived as non-pathogenic symbionts found inside plants since they cause no symptoms of disease on the host plant. Soil conditions and geography among other factors contribute to the type(s) of endophytes isolated from plants. Our research interest is the antibacterial activity of secondary metabolite crude extracts from the medicinal plant Solanum mauritianum and its bacterial endophytes. Fresh, healthy stems of S. mauritianum were collected, washed, surface sterilized, macerated in PBS, inoculated in the nutrient agar plates, and incubated for 5 days at 30 °C. Amplification and sequencing of the 16S rRNA gene was applied to identify the isolated bacterial endophytes. These endophytes were then grown in nutrient broth for 7–14 days, after which sterilized Amberlite(®) XAD7HP 20–60 mesh (Merck KGaA, Darmstadt, Germany) resin was added to each culture to adsorb the secondary metabolites, which were later extracted using ethyl acetate. Concentrated crude extracts from each bacterial endophyte were tested for antibacterial activity against 11 pathogenic bacteria and two human cancer cell lines. In this study, a total of three bacterial endophytes of the Pantoea genus were identified from the stem of S. mauritianum. The antibacterial test showed that crude secondary metabolites of the endophytes and stem of S. mauritianum possessed antibacterial properties against pathogenic microbes such as Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa, with concentrations showing inhibition ranging from 0.0625 to 8.0000 mg/mL. The anticancer analysis showed an increase in cell proliferation when A549 lung carcinoma and UMG87 glioblastoma cell lines were treated with both the plant and endophytes’ crude extracts. As far as we know, this is the first study of its kind on Solanum mauritianum in South Africa showing S. mauritianum endophytes having activity against some of the common human pathogenic organisms.