Sensitizing of β-lactam resistance by tannic acid in methicillin-resistant S. aureus.

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) infections treatment of which is hard and failed, due to being resistant to all types of β-lactams, have been emerged in hospitals and community. Long-term usage of antibiotics and over doses of antibiotics used in the treatment of infections cause bacteria to develop resistance to antibiotics. β-lactams combined with tannic acid can be a good alternative to sensitize the resistance of β-lactams used in the treatment of MRSA, due to their synergistic activities. In this study, after minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) of sole tannic acid and β-lactam were investigated for each isolate, the synergistic activities of β-lactams combined with tannic acid against one MRSA ATCC 43300 and four MRSA clinical isolates were investigated with the concentrations starting at four fold of MICs of sole treatments of tannic acid and β-lactam by using checkerboard assay. To investigate sole and combination activities of tannic acid and β-lactams, MIC and MBCs were observed. Results of this study showed that the activities of β-lactams combined with tannic acid were synergistic and partially synergistic against MRSA isolates with FIC indexes ranged from 0.174 to 0.477 and 0.562 to 0.850, respectively. MIC of β-lactams were decreased 2-16 fold by sub-inhibitory concentrations of tannic acid without toxicity. Alternative treatment options of natural compounds such as tannic acid and β-lactams must be investigated further and developed to overcome the emergence of β-lactam resistance and treat MRSA infections by sensitizing the resistance of β-lactams.