The findings, reported in this month's Gastroenterology (DOI:10.1053/j.gastro.2003.11.019), offer considerable potential for food makers previously restricted to adding bacteria to fermented foods like yoghurt.
The study, by researchers at the University of California, San Diego School of Medicine and the Shaare Zedek Medical Center in Jerusalem, Israel, also reveals a mechanism that can be used to determine and to select which probiotic bacteria are best for patients with IBD.
The addition of probiotic bacteria has until now been limited to dairy products such as yoghurt because it was thought that they needed to be live to have any effect. Adding live bacteria to other foods would result in fermentation, changing the taste, texture and freshness on an hourly basis.
But the new research suggests that the metabolic activity of probiotics is not in fact key to their protective effect.
The researchers used gamma radiation to reduce the metabolic activity of probiotic bacteria to a minimum. Previous studies, using heat to inactivate the bacteria, destroyed the cellular structure and beneficial aspects.
The irradiated probiotics were given to mice with experimentally induced colitis, which is similar to human IBD. The irradiated probiotics effectively improved the colitis symptoms, as did the administration of viable, 'live' bacteria to another group of mice with colitis. This indicated that inactivated probiotics were as effective as live probiotics.
The scientists say that the beneficial, anti-inflammatory activities seen with the inactivated probiotics could be the product of the innate immune system, the body's instant response to invasion by pathogens.
The European probiotics market is forecast to more than triple in value from €34.6 million currently to €118.5 million in 2010, according to recent statistics from Frost & Sullivan. But the market research firm also estimated that its gut health cousin, prebiotics, would be helped by much wider scope in applications, as prebiotic ingredients are easily formulated into a number of different foods, including baked goods and even drinks.
The new research could however open a vast range of new application areas to probiotics too. Gut health is currently driving sales of functional foods in Europe, according to a Datamonitor report, outpacing those foods targeting consumers at risk of heart or bone diseases.
In addition to studying the normal and irradiated probiotics on mice, the researchers also tested a synthetic form of bacterial DNA called immunostimulatory (ISS) oligonucleotide (ODN), a short segment of synthetic DNA with immunostimulatory properties, which mimics bacterial DNA. In a previously published paper in Gastroenterology, ISS-ODN had been found to reduce the harmful effects of experimental colitis in mice, indicating that it worked in a manner similar to probiotics.
Evaluation of the immunostimulatory activities of probiotics may also provide an easy screening system for the selection of probiotic bacteria prior to their clinical use, noted the study's first author, Daniel Rachmilewitz, from the Shaare Zedek Medical Center.