Synergistic antibacterial effect of curcumin against methicillin-resistant Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) are spread among infected patients, with infection rates increasing at an alarming rate. Furthermore, increased resistance to antibiotics has resulted in serious challenges in the treatment of infectious diseases worldwide. Under the selection pressure of exposure to antibiotics, microorganisms evolve to survive against the new conditions imposed by therapy. Therefore, there exists a need to develop alternative natural or combination drug therapies. Curcumin (CCM), a natural polyphenolic flavonoid isolated from the rhizome of a plant, Curcuma longa Linné., has been found to possess many beneficial biological activities. The aim of this study was to investigate the synergistic effect of curcumin and antibiotics as well as to determine the antibacterial activity of CCM against specific MRSA strains. The antibacterial activity of CCM was assessed by the broth microdilution method (by calculating the minimal inhibitory concentration [MIC]), checkerboard dilution test, and time-kill assay. Antimicrobial activity of CCM was observed against all tested strains. The MICs of CCM against 10 strains of S. aureus ranged from 125 to 250 µg/ml. In the checkerboard test, CCM markedly reduced the MICs of the antibiotics oxacillin (OXI), ampicillin (AMP), ciprofloxacin (CIP), and norfloxacin (NOR) used against MRSA. The time-kill curves showed that a combined CCM and OXI treatment reduced the bacterial counts below the lowest detectable limit after 24h. This study suggested that CCM reduced the MICs of several antibiotics tested, notably of OXI, AMP, CIP, and NOR, and that CCM in combination with antibiotics could lead to the development of new combination of antibiotics against MRSA infection.

Synergistic effect of rhein in combination with ampicillin or oxacillin against methicillin-resistant Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium responsible for a number of infections in humans that are difficult to treat, and as a result, is a substantial contributor to morbidity and mortality. In the present study, in search of natural products capable of inhibiting this multidrug-resistant bacterium, we investigated the antimicrobial activity of rhein isolated from Rheum palmatum L. (Polygonaceae) against 16 different strains of the bacterium. New antimicrobial activity was found using the paper disc diffusion method [minimal inhibitory concentrations (MICs)], MTT test and checkerboard dilution test. Against the 16 strains, the disc diffusion test was in the range of 20-29 mm and the MICs of rhein were in the range of 7.8-31.25 µg/ml. From these results we performed the checkerboard test to determine the synergism of rhein in combination with ampicillin (AM) or oxacillin (OX) against all strains. The combined activity of rhein and the two antimicrobial agents (AM and OX) against all strains resulted in a fractional inhibitory concentration index ranging from 0.28-1 and from 0.18-1, respectively. The effect of rhein with AM and OX was found to be synergistic or partially synergistic. We found that rhein reduced the MICs of AM and OX. Rhein in combination with AM or OX could lead to the development of new combinations of antibiotics against MRSA infection.