In Vitro effects of petroleum ether, dichloromethane, methanolic and aqueous leaf extracts of Eucalyptus grandis on selected multidrug-resistant bacteria

Abstract

Background The emergence and spread of antimicrobial resistance is of grave concern, requiring the search for newer and more effective antimicrobials to combat infections caused by resistant microbes. This study assessed the antimicrobial effects of Eucalyptus grandis crude extracts against selected multidrug resistant bacteria. Methodology Four different crude leaf extracts of E. grandis were prepared using petroleum ether, dichloromethane, methanol, and water, with the aid of the Soxhlet extraction method. These were screened against methicillin-resistant Staphylococcus aureus (MRSA), multidrug resistant Pseudomonas aeruginosa, and multidrug resistant Escherichia coli, using the agar well diffusion method. Phytochemical screening was carried out to evaluate the bioactive phytochemical constituents responsible for the antimicrobial effect. Results Each of the extracts, except for the one prepared from water, had antimicrobial activity against the screened bacteria. The non-polar petroleum ether extract had the highest antimicrobial activity (19.33–24.33 mm), including bactericidal effects, compared to the medium polar dichloromethane and polar methanol extracts, which recorded zone diameter ranges of 14.33–16.67 mm and 16.33–17.67 mm, respectively. The Gram-negative bacteria (E. coli and P. aeruginosa) were the least susceptible in comparison with the Gram-positive bacterium (MRSA), probably owing to differences in their cell wall structures. Furthermore, phytochemical screening indicated the presence of alkaloids, tannins, saponins, terpenoids, and flavonoids. Conclusion The findings suggest that E. grandis could be potentially useful in the treatment of infections caused by multidrug resistant bacteria.