In Vitro Evaluation of Antibacterial activity of Zanthoxylum chalybeum Engl. crude extracts against selected ESKAPE pathogens

• Zanthoxylum chalybeum Engl. is a deciduous plant native to East and Southern Africa. • Z. chalybeum exhibited antimicrobial activity against normal and multi drug resistant bacteria. • Acetone extract showed high activity against MDR P. aeruginosa and K. pneumonia. • Z. chalybeum is a potential source of antimicrobial agents for MDR infections. Bacterial resistance is a major problem that threatens the health systems globally. The problem is compounded by the emergence of Multidrug resistance (MDR) pathogens such as ESKAPE pathogens. Given the MDR pathogen mortality projections that exceed 10 million per annum by 2050, there is a need to continuously search for new therapies. Zanthoxylum chalybeum leaf and bark material was extracted with solvents (hexane, chloroform, Dichloromethane, and methanol), to determine its chemical diversity and antimicrobial potential against normal and multi drug resistant strains of Staphylococcus aureus, Pseudomonas aeruginosa and Klebsiella pneumoniae . All crude extracts were effective particularly against Gram negative resistant strains achieving an MIC of 0.156 against P. aeruginosa and 0.625 against K. pneumoniae , values that are even lower than the positive control. Qualitative phytochemical screening was carried out using standard methods, which demonstrated the presence of phenolic compounds, tannins and terpenoids in all extracts. Thin layer chromatography and bioautography revealed clear zones at Rf values between 0.43 and 0.47 (spot A) in all but the leaf methanol extract in all bacteria, and spot B at Rf 0.28 in the leaf acetone and leaf DCM extracts. The spots represented terpenoids and flavonoids respectively. These results underscore the therapeutic potential of Z. chalybeum as a source of novel antibacterial agents, particularly in addressing MDR bacterial infections - a critical and growing global health crisis. Although this study focused on only three of the six ESKAPE pathogens which represent a pressing challenge in antimicrobial resistance, the findings contribute meaningfully to ongoing efforts aimed at combating these high priority pathogens.