Tips from the Journals of the American Society for Microbiology: May 2002

May 13, 2002

Antimicrobial Properties of Licorice Extract

An extract from the roots of the licorice plant is active against a number of microorganisms that can cause food contamination and may be an effective natural alternative to chemical preservatives. Researchers from the Higashimaru Shoyu Company in Japan report their findings in the May 2002 issue of the journal Antimicrobial Agents and Chemotherapy.

Licorice, the root and rhizome of the Glycyrrhiza species, has been used for centuries as a medicine because of its wide-ranging therapeutic properties and recent chemical analyses have found a wide variety of bioactive compounds in licorice. The researchers tested the extract, a compound known as licochalcone A, on 17 food spoilage microorganisms. They found that while the extract was not effective against fungi and gram-negative bacteria, it was effective against all gram-positive bacteria, especially the spore-forming Bacillus species.

"A recent trend in food processing is to avoid the use of chemical preservatives; thus, natural antimicrobial alternatives are required," say the researchers. "In the present study, salt-, heat-, and protease-resistant licochalcone A was suggested to be a promising lead compound for the development of agents against spore-forming bacteria."

(R. Tsukiyama, H. Katsura, N. Tokuriki and M. Kobayashi. 2002. Antibacterial activity of licochalcone A against spore-forming bacteria. Antimicrobial Agents and Chemotherapy, 46: 1226-1230.)

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Milk from Vaccinated Cows Prevents Cavities

A daily dose of milk from cows vaccinated against Streptococcus mutans may help prevent cavities caused by the bacteria, say researchers from Kyushu University in Japan. They report their findings in the May 2002 issue of the journal Infection and Immunity.

S. mutans has been strongly implicated as a cause of dental caries in humans. In the study, the researchers examined the effects of bovine milk containing antibodies against S. mutans on dental caries in rats infected with the bacteria. Rats that received the immune milk has significantly less dental caries than those that received non-immune milk.

"In this study, immune milk clearly suppressed caries development in a rat model," say the researchers. "This immune milk might be an effective tool for controlling dental caries in humans."

(M. Mitoma, T. Oho, N. Michibata, K. Okano, Y. Nakano, M. Fukuyama and T. Koga. 2002. Passive immunization with bovine milk containing antibodies to a cell surface protein antigen-glucosyltransferase fusion protein protects rats against dental caries. Infection and Immunity, 70: 2721-2724.)

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Treatment Delays Scrapie Onset

Researchers from Scotland have developed a treatment that significantly delays the onset of scrapie in mice and may serve as a strategy for early treatment of other transmissible spongiform encephalopathies (TSEs). They report their findings in the May 2002 issue of the Journal of Virology.

TSEs, or "prion diseases", such as scrapie, bovine spongiform encephalopathy and Creutzfeldt-Jakob disease in humans are infectious neurodegenerative diseases believed to be caused by a protein. After infection, but before symptoms appear, the protein replicates and builds up in the lymphoid tissues. The researchers observed that the infection required a specific immune protein, called tumor necrosis factor (TNF), to spread from the lymphoid tissues to the central nervous system and the brain. In this study, the researchers used a compound that blocked the TNF receptors (TNFR) in mice experimentally infected with scrapie. A single treatment before or shortly after infection significantly delayed the onset of the disease in the central nervous system.

"We conclude that treatments that specifically inhibit the TNFR signaling pathway may present an opportunity for early intervention in peripherally transmitted TSEs," say the researchers.

(N.A. Mabbott, G. McGovern, M. Jeffrey and M.E. Bruce. 2002. Temporary blockade of the tumor necrosis factor receptor signaling pathway impedes the spread of scrapie to the brain. Journal of Virology, 76: 5131-5139.)
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Full copies of each article can be accessed through the ASM website at: http://www.asmusa.org/pcsrc/tip.htm

American Society for Microbiology

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