Abstract Description

The escalating threat of antibiotic resistance, projected to cause 10 million deaths annually by 2050, demands alternative therapeutic strategies. Unlike bactericidal agents that promote resistance through selective pressure, targeting non-lethal bacterial processes such as quorum sensing (QS) and biofilm formation offers a promising approach. Endophytic bacteria are known producers of diverse bioactive compounds with therapeutic potential (antimicrobial, antifungal, antiviral, immunosuppressive, and antitumor). This study, therefore, investigated the QS and anti-biofilm activities of secondary metabolites from endophytic bacteria species isolated from Kigelia africana leaves. Fifteen endophytic bacterial isolates were cultured in medium mannitol using submerged fermentation for 7 d, followed by extraction using ethyl acetate. Extracts (100-1600 µg/ml) were assessed for QS inhibition using Chromobacterium species as biosensors to evaluate their potential to inhibit Gram-negative acyl homoserine lactone (AHL) signalling. Methicillin-resistant Staphylococcus aureus ATCC 43300 (MRSA), S. aureus ATCC 6358, Pseudomonas aeruginosa ATCC 27853 and Acinetobacter baumannii ATCC 19606 were used to determine the extracts’ ability to inhibit initial adhesion and disrupt mature biofilm. Extracts were subjected to gas chromatography-mass spectrometry (GC-MS) and Fourier Transform Infrared (FTIR) spectroscopy to determine metabolite profiles. More than half of the endophytic bacteria (53.3%) belong to the Bacillus genus. Only 13.3% of the endophytes inhibited long-chain AHL. However, several extracts demonstrated promising anti-biofilm effects. Against S. aureus, 53.3% (8/15) of extracts inhibited initial adhesion, and 13.3% (2/15) disrupted mature biofilm in MRSA. For A. baumannii, only 13.3% (2/15) inhibited initial adhesion, while 20% (3/15) disrupted mature biofilm. GC-MS analysis revealed bioactive compounds including 1-propanol, 2,2-dimethyl-, acetate; 2,5-hexanedione 3,4-dihydroxy-3,4-dimethyl-; isovaline, 3-hydroxy-; trans-cinnamic acid and heptadecane, 2,6,10,15-tetramethyl, which may be responsible for the observed QS and antibiofilm activities. FTIR analysis revealed the presence of ketone, carboxylic acid, ester, alkane, alkene, alcohol and amine functional groups in the extracts. Given the role of QS and biofilms in high-level antibiotic tolerance, these findings highlight the potential of bacterial endophyte-derived metabolites from K. africana as promising leads for QS inhibition and anti-biofilm agents in pharmaceutical development.