Chemical profiling and antibacterial activity of fermented papaya (Carica papaya) and lemon (Citrus limon) peel solutions: In vitro, in vivo, and in silico studies

Abstract

Antimicrobial resistance has driven the search for natural antibacterial agents, including fermentation-derived metabolites. The aim of this study was to evaluate the antibacterial activity and chemical profile of a fermented papaya and lemon peel solution against Staphylococcus aureus and Pseudomonas aeruginosa using an integrated in vitro, in vivo, and in silico approach. Antibacterial activity was assessed using disc diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) assays, followed by validation in a Drosophila melanogaster infection model. Chemical profiling was performed using liquid chromatography-high-resolution mass spectrometry (LC-HRMS), followed by molecular docking and molecular dynamics simulation. In the disc diffusion assay, the fermented solution showed greater activity against S. aureus than against P. aeruginosa, with the largest inhibition zones observed at a 15% concentration (12.26±0.30 mm and 8.49±0.68 mm, respectively). In infected D. melanogaster larvae, 5% and 10% fermented solution significantly improved survival compared with infection controls and reduced bacterial recovery to below the detection limit of 1×10⁴ colony-forming unit (CFU)/mL under the tested conditions. Gene expression analysis showed increased expression of defensin and catalase, suggesting modulation of innate immune and antioxidant responses during S. aureus infection. LC-HRMS identified 18 compounds, and molecular docking indicated that luteolin 7-O-rutinoside had the strongest predicted binding affinity toward DNA gyrase and transpeptidase penicillin-binding protein 2a, with docking scores of –9.8 and –10.4 kcal/mol, respectively. These findings suggest that the fermented papaya and lemon peel solution exhibits antibacterial activity against S. aureus and may act through complementary antibacterial and host-response mechanisms. Further studies using isolated compounds, defined detection limits, mammalian models, and clinical bacterial isolates are needed to validate its therapeutic relevance.