Antimicrobial activity of quinine derivatives against human pathogenic bacteria

Nowadays, the antimicrobial resistance is considered as one of the greatest concern facing human health, as many of bacterial strains had become resistant to available antibiotics. The misuse of antibiotics has potentially reduced the efficacy of drugs, concurrent with the increase of bacterial resistance to commercially available drugs. Therefore, the discovery of effective antimicrobial agents are desperately needed to overcome this epidemic, especially from traditional medical plants and their derivatives. Quinine is a natural alkaloid from the bark of the cinchona tree that has been used for years as an antimalarial drug. Various literatures also regarded an antibacterial effect of quinine against both Gram-positive and Gram-negative pathogenic microorganisms. With this vision, a series of some novel quinine derivatives were synthesized and their biological activities against pathogenic bacteria were assessed. This present study therefore attempted to examine the antimicrobial properties of quinine-derived compounds and their Minimal Inhibitory of Concentration (MIC) against common pathogenic bacteria strains, e.g. Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus substillis. Disk diffusion test was performed for screening of antimicrobial activity of quinine derivatives. The results were evaluated and compared with references drug streptomycin. It was found that quinine derivatives showed moderate antimicrobial activity as compared with quinine itself on tested pathogenic bacterial strains. Ester quinine propionate was found to give the highest antibacterial activity among other derivatives, with a range inhibition zone from 9 to 23.5 mm to bacteria strains, compared to streptomycin with a range of inhibition zone from 8 to 12 mm. Further studies are needed to assess the bactericidal mechanisms of those derivative compounds.