TLC-bioautography-guided identification and assessment of the antibacterial compounds from Feijoa sellowiana

A rapid procedure was developed for the targeted isolation and assessment of antibacterial compounds from plant-based materials. The effectiveness of this method was demonstrated using Feijoa sellowiana fruit peels.

The objectives of this study are as follows: develop an efficient procedure utilizing direct thin-layer chromatography (TLC)-bioautography to facilitate the targeting, identification, and purification of antibacterial compounds from plant extracts and delineate a method based on TLC-bioautography to determine the minimum effective dose (MED), alongside a colorimetric broth microdilution aided by high-performance liquid chromatography (HPLC) for evaluating the isolated active compounds.

Active compounds were targeted using TLC-bioautography against Staphylococcus aureus, and the identification was achieved through liquid chromatography-mass spectrometry (LC-MS) combined with Compound Discoverer. Purification was carried out using a customized separation method. The structure was confirmed using nuclear magnetic resonance (NMR) spectroscopy. The MED, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) were determined by two enhanced antibacterial assays.

The main antibacterial compound identified was flavone. A TLC-bioautography-based antibacterial assay and a colorimetric broth microdilution assisted by HPLC were described as the enhanced antibacterial assay protocols. The MED, MIC, and MBC of flavone against S. aureus were found to be 4.2-5.2 μg/cm², 225-275 μg/mL, and 550-650 μg/mL, respectively. Similarly, the MED, MIC, and MBC against Escherichia coli were determined to be 5.2-6.1 μg/cm², 325-375 μg/mL, and 375-425 μg/mL, respectively.

This study proposed an enhanced bioassay-guided separation technique for the isolation of antibacterial compounds from plants, along with two improved methods for assessing the antibacterial efficacy of insoluble or colored compounds.