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Tips from the Journals of the American Society for Microbiology

September 16, 2004

Combination of Cranberry and Oregano Extracts May Inhibit Bacteria in Meat and Fish

Cranberry and oregano extracts combined with lactic acid may inhibit the growth of bacteria in meat and fish say researchers from Massachusetts. Their findings appear in the September 2004 issue of the journal Applied and Environmental Microbiology.

Listeria monocytogenes, the cause of many food-borne illnesses throughout North America and Europe, is a bacterium capable of growing in refrigerated temperatures making it very difficult to control. Listeriosis carries a high mortality rate and is therefore regarded as a serious problem worldwide.

In the study a combination of oregano and cranberry extracts (75% oregano and 25% cranberry) was applied to meat and fish and refrigerated at 39 degrees Fahrenheit. Antimicrobial activity in meat and fish increased as a result of treatment with the mixture and was further enhanced by the addition of lactic acid.

"Oregano and cranberry, useful botanicals generally regarded as safe for food flavoring and as functional ingredients are known for their antimicrobial activity linked to the phenolic moiety and therefore are suitable as antimicrobial natural extracts when effectively combined with lactic acid," say the researchers.

(Y.T. Lin, R.G. Labbe, K. Shetty. 2004. Inhibition of Listeria monocytogenes in fish and meat systems by use of oregano and cranberry phytochemical synergies. Applied and Environmental Microbiology, 70. 9: 5672-5678.)

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Bacteria in Dental Plaque of Children May Predict Gum Disease as Adult

The presence of certain bacteria in dental plaque of children could help predict their risk of developing periodontal disease as adults say researchers from Eastman Dental Institute, London, United Kingdom. Their findings appear in the September 2004 issue of the Journal of Clinical Microbiology.

Gingivitis is the continuous accumulation of dental plaque caused by poor oral hygiene. If left untreated gingivitis can develop into periodontal disease, an infection in the gums which can cause loss of bone and teeth. Although periodontal disease rarely occurs in healthy children, research suggests that the bacteria that cause infection later in life may be present at a very early age.

"Although periodontal disease is rare in healthy children, it is important to investigate the presence of periodontal pathogens as the permanent teeth start to erupt," say the researchers.

In the study, DNA was taken from plaque samples in children ages five to nine, with and without gingivitis, and tested for the presence of Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Tannerella forsythensis. The presence of P. gingivalis and A. actinomycetemcomitans was comparable in both groups, however T. forsythensis was detected more frequently in children without gingivitis appearing in 65% of the samples as opposed to 45% of the samples from kids with gingivitis.

"The results of this study have shown that the three pathogens can be detected in the plaque of children with and without gingivitis and specifically that T. forsythensis is associated with dental plaque found at sites without gingivitis," say the researchers. "Further work is needed to analyze the significance of finding a greater prevalence of T. forsythensis in children with no gingivitis than in children with gingivitis as observed."

(G.P. Gafan, V.S. Lucas, G.J. Roberts, A. Petrie, M. Wilson, D.A. Spratt. 2004. Prevalence of periodontal pathogens in dental plaque of children. Journal of Clinical Microbiology, 42. 9: 4141-4146.)

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Refrigerating Milk Harms Cheese-making Bacteria

Refrigeration of raw milk for as little at 24 hours can significantly decrease levels of bacteria responsible for the development of the desirable qualities of raw-milk cheeses while at the same time increase the levels of undesirable contaminants and foodborne diseases, say researchers from France. They report their findings in the September 2004 issue of the journal Applied and Environmental Microbiology.

"Until recently, the bacterial community of raw milk was described by classical microbiological methods, which are generally long and tedious, and allow only a partial inventory of the bacterial microflora," say the researchers. "New molecular approaches based on direct analyses of DNA (or RNA) in its environment without microbial enrichment have allowed for precise descriptions of microbial dynamics in complex ecosystems."

Using these new technologies, the researchers analyzed bacterial populations in fresh raw milk, and raw milk that had been refrigerated for 24 hours.

"Many of the species identified after refrigeration were present in the initial sample. However, the relative proportions of bacterial were clearly altered by refrigeration," say the researchers.

In the fresh samples, the dominant bacterial population was Lactobacillus lactis, a species of bacteria that is commonly used as a starter culture for many cheeses. After refrigeration, the researchers found a significant decrease in L. lactis population. In addition, they detected increases in a variety of other bacteria, including Listeria monocytogenes, a contaminant that is common cause of foodborne disease.

"The results obtained are of interest not only for their contribution to the knowledge on the bacterial flora of raw milk samples but also essentially for elucidating the power of these molecular approaches to rapidly and precisely describe the consequences of a simple process, milk refrigeration, on the quality of dairy products and its impact on health," say the researchers.

(V. Lafarge, J.C. Ogier, V. Girard, V. Maladen, J.Y. Leveau, A. Gruss, A. Delacroix-Buchet. 2004. Raw cow milk bacterial population shifts attributable to refrigeration. Applied and Environmental Microbiology, 70. 9: 5644-5650.)
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American Society for Microbiology

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