Phytochemical screening and inhibitory effects of Catha edulis Forsk extracts on oxidation, growth, biofilm and quorum sensing of selected pathogens

The treatment of infectious diseases is increasingly challenging due to the emergence and re-emergence of antibiotic-resistant bacteria. Plant-derived natural products are being explored as potential solutions to this global threat. This study investigated the phytochemical composition of Catha edulis and biological properties of its extracts, focusing on their potential as antioxidants and antimicrobials. Gas chromatography/mass spectrometry (GC/MS) of the methanol extract (MeOHE) fractions revealed 11 compounds in dichloromethane fraction (DCMF) and 30 compounds in ethyl acetate fraction (EAF), many of which possess bioactive functions as antioxidants and antimicrobials. Phytol was detected at 60.32 %, not reported before in C. edulis. The antioxidation potential of extracts was assayed by radical scavenging activity (RSA), and the IC₅₀ values ranged from 68.2 to 89.3 µg/mL, respectively indicating good antioxidant potency. In the disc diffusion assay against representative pathogenic bacteria, the extracts exhibited an inhibition order of EAF > DCMF > MeOHE in the 31-75 % range. The minimum inhibitory concentration (MIC) for MeOHE and DCMF were in the 0.5 - >1 mg/mL range, while the minimum bactericidal concentration (MBC) were from 2 to > 2 mg/mL. EAF showed a MIC and MBC in the 0.5---1 mg/mL and 1---2 mg/mL range, suggesting better inhibition potential. The tolerance test values showed bactericidal activity against all the tested bacteria. The minimum biofilm inhibitory concentration (MBIC) values of DCMF were 250 to > 500 µg/mL, while EAF ranged from 125 to 500 µg/mL, indicating effective inhibition of biofilm formation. The anti-quorum sensing (anti-QS) activity of DCMF and EAF on P. aeruginosa showed 55.8 % and 51.4 % inhibition of pyocyanin production at 500 µg/mL. These results suggest that DCMF and EAF of C. edulis are potent antioxidants and antimicrobials, potentially reducing the load of pathogens. To our best knowledge, this is the first report of antibiofilm and anti-QS activities of C. edulis extracts on pathogenic bacteria included in the Pathogen Priority List.