Antibacterial evaluation of gallic acid and its derivatives against a panel of multi-drug resistant bacteria.

BACKGROUND: Infectious diseases are the second highest cause of deaths worldwide. Pathogenic bacteria have been growing tremendous resistance against antibiotics which has put additional burden on healthcare systems. Gallic acid belongs to a naturally occurring phenolic class of compounds and is known to possess a wide spectrum of antimicrobial activities.

AIMS & OBJECTIVES: In this study, we have synthesized thirteen derivatives of gallic acid and evaluated their antibacterial potential against seven multi-drug resistant bacteria as well as cytotoxicity effects against human embryonic kidney cell line in vitro.

METHODS: 13 compounds were successfully synthesized with moderate to good yield and evaluated. Synthesized derivatives were characterized by using nuclear magnetic resonance spectroscopy, mass spectrometry, and Fourier transformation infrared spectroscopy. Antibacterial activity was determined by using microdilution assay whereas MTT assay was utilized to study cytotoxicity.

RESULTS: The results of antibacterial assay showed that seven out of thirteen compounds exhibited antibacterial effects with compound 6 and 13 being most potent against Staphylococcus aureus (MIC 56 µg/mL) and Salmonella enterica (MIC 475 µg/mL) respectively. On the other hand, most of these compounds showed lower cytotoxicity against human embryonic kidney cells (HEK 293) with IC50 values ranging in more than 700 µg/mL.

CONCLUSION: Notably, compound 13 was found not toxic for as high as 5000 µg/mL. These findings suggest that the present synthetic derivatives of gallic acid hold potential for further studies in the development of potent antibacterial agents.