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Volume 38, Number 5, October 2005

Effect of melanin produced by a recombinant Escherichia coli on antibacterial activity of antibiotics


Wen-Po Lin, Hsing-Lung Lai, Yi-Lin Liu, Yin-Mei Chiung, Chia-Yang Shiau, Jun-Ming Han, Chuen-Mi Yang, Yu-Tien Liu
Institute of Microbiology and Immunology, National Defense Medical Center, Taipei; Department of Dermatology, Veteran General Hospital, Taipei; Institute of Occupational Safety and Health, Taipei; Institute of Medical Sciences, National Defense Medical Center, Taipei; and Institute of Preventive Medicine, National Defense Medical Center, Taipei, Taiwan

Received: March 21, 2005    Revised: May 25, 2005    Accepted: July 1, 2005   

 

Corresponding author:

Yu-Tien Liu, Ph.D., Professor of Microbiology, Institute of Microbiology and Immunology, National Defense Medical Center, P.O. Box 90048-505, Neihu, Taipei, Taiwan. E-mail: ytliu@mail.ndmctsgh.edu.tw This e-mail address is being protected from spam bots, you need JavaScript enabled to view it

 



 

Methods:

A recombinant plasmid, pYL-1, containing a tyrosinase gene whose expression is under the control of a phage T5 promoter and 2 lac operators, was constructed. Escherichia coli JM109 harboring pYL-1 was used for production of bacterial melanin. A simple procedure for the isolation and purification of melanin was developed. The ultraviolet (UV)-visible light absorption spectra of melanin prepared by chemical synthesis and derived from different organisms, including bacteria, a plant and an animal source, were determined. Melanins produced by both bacteria and chemical synthesis showed a steady increase of absorption at wavelengths of UV light ranging from approximately 200-400 nm, while melanin derived either from plant or animal sources showed an additional discrete absorption peak at wavelength 280 nm upon a similar steady increase of absorption. This additional absorption peak could be due to the presence of protein-bound melanins in animal and plant sources while a free form of melanin was obtained from bacteria and chemical synthesis. Analysis of the effect of bacterial melanin on the activity of antibiotics against E. coli revealed that the activities of polymyxin B, kanamycin, tetracycline, and ampicillin were markedly reduced in the presence of melanin, whereas the activity of norfloxacin was not affected. The reduction of the antibacterial activity may result directly from the interaction of antibiotics with melanin. However, the mechanism of this interaction remains to be demonstrated.

 



 

Key words:

Anti-bacterial agents, Escherichia coli, melanin, microbial sensitivity tests, plasmids


 



 

J Microbiol Immunol Infect 2005;38:320-326.