"Good" bacteria that live in our intestines have been linked with a variety of health benefits, from fighting disease to preventing obesity. In a new study, Kriston Ganguli of Massachusetts General Hospital for Children and Harvard Medical School and her colleagues have discovered another advantage to these friendly microscopic tenants: Chemicals secreted by good bacteria that typically live in the intestines of babies could reduce the frequency and severity of a common and often-lethal disease of premature infants.
This disease, known as necrotizing enterocolitis (NEC), affects between 8 and 13 percent of very low birthweight infants (those under 3 pounds, 4 ounces), and up to half of the infants with this condition will die. As babies develop the collection of gut bacteria that colonize healthy intestines, those with NEC have an extreme inflammatory reaction that leads to damage and death of these tissues that often requires surgery to correct. Steroids are one of the few currently available ways to prevent NEC, but their use can cause undesirable complications.
Recent clinical trials of probiotics—live microbes taken as dietary supplements to promote health—have shown promise in reducing both the incidence and severity of NEC. However, in the U.S., the Food and Drug Administration does not sanction the use of whole bacteria in premature infants. Seeking a different tact that avoids the use of the bacteria themselves, scientists in the new study investigated whether secretions from probiotic bacteria could prevent NEC.
The article is titled "Probiotics prevent necrotizing enterocolitis by modulating enterocyte genes that regulate innate immune-mediated inflammation." It appears in the American Journal of Physiology—Gastrointestinal and Liver Physiology (http://bit.ly/11C6WHf) published by the American Physiological Society.
As a model for a baby's immature gut, the researchers used intestinal tissue from infants with NEC as well as fetal intestinal tissues. The researchers also grew two probiotic strains of bacteria, L. acidophilus and B. infantus, in liquid culture medium, but removed the bacteria from the cultures. The material in which these bacteria were grown, known as the probiotic conditioned medium (PCM), contained secretions the bacteria left behind.
They then exposed human immature and mature intestinal tissues to either PCM or to material usually used to grow bacteria that had never contained microbes. They also exposed some tissues to a compound derived from bacteria that's known to cause an inflammatory response.
They analyzed the tissues for expression of genes known to respond to inflammation and looked at the effects of secretions from the two different probiotic strains separately to determine whether one had a greater anti-inflammatory effect than the other.
The scientists found that treatment with just the PCM significantly reduced inflammation in both immature intestinal tissue and tissue from infants with NEC.
When the researchers analyzed gene expression in the PCM-exposed tissue, they found reduced activity of several genes linked with inflammation. Interestingly, PCM exposure did not affect mature intestinal tissue.