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Molecules 2011, 16(8), 6656-6666; doi:10.3390/molecules16086656

In Vitro Synergy of Biochanin A and Ciprofloxacin against Clinical Isolates of Staphylococcus aureus

1,†, 1,†, 1,†, 1,†, 1,†, 2,†, 1,†, 1, 1, 1, 1, 1,*  and 1,3,4,*
1 Key Laboratory of Zoonosis Research, Ministry of Education, Institute of Zoonosis, College of Animal Science and Veterinary Medicine, Jilin University, Changchun 130062, China 2 Department of Food Quality and Safety, College of Quartermaster Technology, Jilin University, Changchun 130062, China 3 Institute of Pathogen Biology, Chinese Academy of Medical Sciences, Beijing 100730, China 4 State Key Laboratory for Molecular Virology and Genetic Engineering, Chinese Center for Disease Control and Prevention, Beijing 100176, China These authors contributed equally to this work.
* Authors to whom correspondence should be addressed.
Received: 11 July 2011 / Revised: 30 July 2011 / Accepted: 2 August 2011 / Published: 5 August 2011
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Many clinical isolates of Staphylococcus aureus (S. aureus) are resistant to numerous antimicrobials, including the fluoroquinolones (FQs). Flavonoids such as biochanin A (BCA) are compounds that are naturally present in fruits, vegetables, and plant-derived beverages. The goal of this investigation was to study the possible synergy between the antimicrobial agents BCA and ciprofloxacin (CPFX) when used in combination; CPFX was chosen as a representative FQ compound. We used S. aureus strain ATCC 25923 and 11 fluoroquinolone (FQ)-resistant methicillin-resistant S. aureus (MRSA) strains. Results from the drug susceptibility testing and checkerboard assays show that the minimum inhibitory concentration (MIC) of BCA ranged from 64 µg/mL to 512 µg/mL. When BCA was combined with CPFX, the fractional inhibitory concentration index (FICI) data showed that there was synergy in all 12 of the S. aureus strains tested. No antagonistic activity was observed in any of the strains tested. The results of time-kill tests and agar diffusion tests confirm that there was synergy between BCA and CPFX against S. aureus strains. These results suggest that BCA can be combined with FQs to produce a powerful antimicrobial agent.
Keywords: antimycobacterial; biochanin A; ciprofloxacin; Staphylococcus aureus; synergy antimycobacterial; biochanin A; ciprofloxacin; Staphylococcus aureus; synergy
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Liu, G.; Liang, J.-C.; Wang, X.-L.; Li, Z.-H.; Wang, W.; Guo, N.; Wu, X.-P.; Shen, F.-G.; Xing, M.-X.; Liu, L.-H.; Li, L.; Liu, M.-Y.; Yu, L. In Vitro Synergy of Biochanin A and Ciprofloxacin against Clinical Isolates of Staphylococcus aureus. Molecules 2011, 16, 6656-6666.

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