Chronic stress is implicated in the development of irritable bowel syndrome and in the worsening of symptoms of inflammatory bowel disease, such as Crohn's disease, which affects over half a million people in the US.
The new research, published on-line in the journal Gut (10.1136/gut.2005.089739), measured the effects of a commercial probiotic powder on intestinal health of male rats subjected to a daily dose of stress.
Brown Norway rats were fed either a normal diet or a normal diet supplemented with a probiotic mixture. The probiotic powder contained Lactobacillus rhamnosus, strain R0011 and Lactobacillus helveticus, strain R0052 (Lacidofil) and was provided by the Montreal-based Institut Rosell-Lallemand.
The two groups were further divided so that half of the probiotic and half of the normal diet groups were subjected to water avoidance stress (WAS), which involved placing the rat on a small platform surrounded by water, for one hour a day for 10 consecutive days.
The other half of each group was subjected to a sham stress for the same time period.
The stress sessions were designed to mimic psychological stress to produce the type of effects that would be seen in the human gut.
At the end of the stress period the intestinal tissues of the animals were examined. The researchers, from Canada and Sweden, found that the presence of harmful bacteria was significantly greater in the WAS rats.
The density of harmful bacteria was measured to be 28.3 and 34.7 bacteria per square millimeter in the ileum and colon of the WAS group, respectively. Rats exposed to chronic stress and supplemented with probiotics had only about 20 percent of these bacterial populations, leading the scientists to conclude that the probiotics were preventing the adherence of harmful bacteria to the cells lining the gut wall.
"Probiotics transiently colonize the gut and competitively exclude pathogenic bacteria from binding," said lead author Mehri Zareie from the University of Toronto.
The researchers also found that supplementation with the probiotic mixture reduced migration of bacteria into the lymph system, and thus prevented an immune response from the hosts.
"These findings indicate that probiotics may provide a novel approach for the management of stress induced intestinal dysfunction.
More in depth studies into the mechanisms of action will allow a better understanding of how probiotics target specific organs in different disease states," concluded the researchers.
Research and development into probiotics continues to attract significant investment, particularly in Europe where the market is considerably more developed than the US.
In spite of this, a report from the Business Communication Company in May 2005 said the US probiotic ingredients, supplements and foods market had risen 19 percent per year over the last two years. It forecast 2005 total sales to reach $764m.
Yogurts, kefirs and cultured drinks are predicted to make up around 65 percent of the US probiotics sales. The BCC report added that, although growth is expected to slow over the next five years, an annual rate of 7.1 percent would put probiotic sales at $1.1bn in 2010.