Survival of Lactobacillus reuteri DSM 17938 and Lactobacillus rhamnosus GG in the Human Gastrointestinal Tract with Daily Consumption of a Low-Fat Probiotic Spread

Probiotics are live microorganisms which, when administered in adequate amounts, confer a health benefit on the host. Therefore, probiotic strains should be able to survive passage through the human gastrointestinal tract. Human gastrointestinal tract survival of probiotics in a low-fat spread matrix has, however, never been tested. The objective of this randomized, double-blind, placebo-controlled human intervention study was to test the human gastrointestinal tract survival of Lactobacillus reuteri DSM 17938 and Lactobacillus rhamnosus GG after daily consumption of a low-fat probiotic spread by using traditional culturing, as well as molecular methods. Forty-two healthy human volunteers were randomly assigned to one of three treatment groups provided with 20 g of placebo spread (n = 13), 20 g of spread with a target dose of 1 × 10⁹ CFU of L. reuteri DSM 17938 (n = 13), or 20 g of spread with a target dose of 5 × 10⁹ CFU of L. rhamnosus GG (n = 16) daily for 3 weeks. Fecal samples were obtained before and after the intervention period. A significant increase, compared to the baseline, in the recovery of viable probiotic lactobacilli in fecal samples was demonstrated after 3 weeks of daily consumption of the spread containing either L. reuteri DSM 17938 or L. rhamnosus GG by selective enumeration. In the placebo group, no increase was detected. The results of selective enumeration were supported by quantitative PCR, detecting a significant increase in DNA resulting from the probiotics after intervention. Overall, our results indicate for the first time that low-fat spread is a suitable carrier for these probiotic strains.The human intestinal microflora or microbiota constitutes a metabolically active microbial environment. This community is relatively stable in the guts of healthy individuals (20). Some of the microbial groups harbor species that are potentially harmful, whereas others, such as the bifidobacteria and lactobacilli, are regarded as beneficial (8). Specific members of the genera Lactobacillus and Bifidobacterium are being applied in functional foods as probiotics (25). Probiotics are live microorganisms which, when administered in adequate amounts, confer a health benefit on the host (9). The current scientific consensus is that probiotics should be alive to exert their beneficial effect in the human gastrointestinal (GI) tract (6). Consequently, probiotics should remain alive in the product, such that the daily effective dose per serving is still present at the end of the shelf life (14). Food matrices, production processes, or product usages that involve heating can affect the viability of probiotics (24).Typically, those members selected for probiotic application are chosen for their resistance to passage through the upper GI tract and thus are able to transiently colonize the gut (25). Human GI tract survival of probiotics should lead to shedding of live cells in fecal samples. GI tract survival is, however, dependent on both the strain and the food matrix involved (27). Fecal recovery of several probiotic strains has been demonstrated in different food matrices, including fermented milk and yoghurt (10, 26, 29), fruit drinks (21), a cereal bar (22), supplements (13, 17, 27), and infant formula (29).For this study, we have selected two well-established probiotic strains to test the suitability of a low-fat spread as a probiotic carrier, namely, Lactobacillus reuteri DSM 17938 (BioGaia, Sweden) and Lactobacillus rhamnosus GG (ATCC 53103; Valio, Finland). L. reuteri DSM 17938 was derived from L. reuteri ATCC 55730 by curing of two plasmids harboring antibiotic resistance genes (23). A series of in vitro experiments confirmed the retention of the functional properties of the daughter strain, as no differences in colony morphology, fermentation patterns, production of reuterin, generation time, mucus-binding ability, or tolerance to bovine bile were found between L. reuteri ATCC 55730 and DSM 17938. The daughter strain is somewhat more resistant to low pH and grows to a higher density in vitro (23). Several studies have been published which provide data on the survival of L. reuteri ATCC 55730 in the human GI tract at doses of 4 × 10⁸ to 1 × 10¹⁰ CFU/day in freeze-dried matrices and chewable tablets (32-34). Furthermore, L. reuteri DSM 17938 was demonstrated to survive human GI tract passage in the same way as L. reuteri ATCC 55730 (23).L. rhamnosus GG has been isolated from a healthy human intestinal flora by Goldin et al. (10). L. rhamnosus GG is relatively resistant to acid and bile, adheres in vitro to epithelial cells, and can produce an antimicrobial substance (10, 15). A wide range of studies have been published which provide data on the survival of L. rhamnosus GG in the human GI tract (3, 4, 10, 18, 19, 27-30), as well as transient colonization of the intestinal microbiota in healthy adults in various formats, including freeze-dried powder, capsules, and tablets or via fermented milk drinks, yoghurt, or fruit juice. Saxelin et al. (28) evaluated the dose-response effect of orally administered L. rhamnosus GG in powder form on fecal colonization in healthy adults, which indicated that consumption of approximately 10¹⁰ to 10¹¹ CFU/day was required to reach detectable levels in fecal samples from volunteers. This was also the case when L. rhamnosus GG was administered in gelatin capsules (29). Additionally, Saxelin et al. (27) observed that milk, but possibly also other protective compounds in food, can improve the survival of L. rhamnosus GG. Fecal recovery of L. rhamnosus GG in milk-based products was shown at dose levels of around 2 × 10⁹ CFU/day.It is, however, not known whether probiotics can survive passage through the human GI tract after the consumption of a low-fat spread. The objective of this randomized, double-blind, placebo-controlled human intervention study was therefore to test the human GI tract survival of L. reuteri DSM 17938 and L. rhamnosus GG after daily consumption of a low-fat probiotic spread by using traditional culturing, as well as molecular methods. The primary outcome parameter of this study was a significant change from the baseline in the number of probiotic bacteria of the respective strains in fecal samples.