The results here indicate that the concentration of fecal mucin does not diminish during an episode of rotavirus diarrhea; the probiotics binding to the intestinal mucus do not thus lose their potential and can be safely used in the treatment of rotavirus diarrhea and in other viral gastrointestinal infections in children. A more rapid exchange of mucus during diarrhea is possible, which may shorten the time for adherence of probiotic bacteria; nevertheless, probiotic bacteria have been shown to enhance the local immune response and to promote recovery from rotavirus diarrhoea (12
The mucous layer in the intestine is relatively thick (up to 400 μm), and it is in a dynamic state, constantly being synthesized by goblet cells and also degraded. The mucous gel is predominantly water (up to 95%), the mucin content is up to 5%, and other components include lipids, free proteins, and salts. The mucins are the large glycoproteins which are the major organic components of mucus, and the protein content of the mucin is 20%, while carbohydrate comprises 70 to 80% by weight. Intestinal mucin has been shown to inhibit the replication of rotavirus in vitro (3
). Calves infected with rotavirus have been shown to have substantially less mucin covering the epithelium of the small intestine and colon than do healthy controls (34
), but, as shown here, human infants, at least well-nourished infants, sustain the level of mucin during rotavirus diarrhea.
In humans lactobacilli colonize the distal small bowel and the large intestine. Different probiotic bacteria possess various mechanisms, including adhesins and/or coaggregation factors, which aid adhesion and colonization (30
). Assessment of bacterial adhesion in vivo is difficult, and in vitro models with cell lines (14
) are commonly applied for that purpose. Human ileostomy glycoproteins have been used as a model for the small-intestinal mucus to investigate adhesion of probiotics, and in vitro adhesion to mucous glycoproteins extracted from feces has been shown to correlate with the adhesion to ileostomy glycoproteins (31
). Thus, in vitro evaluation of the adhesion to human intestinal mucus provides a suitable model for estimating the ability of probiotics to adhere to intestinal surfaces. It has been suggested that adhesion of lactobacilli to human intestinal mucus has a probiotic function in preventing the adhesion to and colonization of damaged tissue sites by invading pathogens (34
). The induction of mucin gene expression is perhaps one of the mechanisms whereby probiotic strains minimize the interplay of other microbes with intestinal mucosal cells and thereby intestinal inflammation (17
In this study, we characterized the bacterial adhesion to human intestinal mucus isolated from feces during a bout of rotavirus diarrhea and during convalescence. Our results confirm that specific probiotics evince significantly different adherence to the intestinal mucus, and no change in adherence occurred during diarrhea. The adhesion is highly species specific. Our results are comparable to those previously obtained in healthy infants (13
). The increased binding of Bb12 in the presence of GG confirms the finding (21
). Probiotic strains of high adherence capacity have been demonstrated to enhance the immunoglobulin A response to rotavirus (12
). The immune response by GG is similar to the adjuvant action of cholera toxin (15
), the adherence properties of which are related to the intensity of the mucosal immune response. GG perhaps influences permeation of antigens through Peyer's patches stimulating an immunoglobulin A-committed B-cell population (12
). Thus, the immune response of probiotic strains and their adherence are in a good relation, as is the case with other antigens; the better the adherence is, the stronger the immune response is, but more experimental work is required before this can be confirmed. This study helps us to choose the specific probiotics for clinical use because excellent adherence continues during rotavirus diarrhea, too.
Conclusions. The concentration of human intestinal mucin and the adherence properties of the probiotic strains are altered only negligibly during or after rotavirus diarrhea compared to the status in healthy children, as tested in vitro. The appropriate combination of probiotics seems to increase adhesion and probably also the immune response and may be beneficial in the treatment and prevention of rotavirus diarrhea, possibilities which future clinical trials will investigate.