Several probiotic strains have been shown to enhance human resistance to infectious disease. It is speculated that these strains may impose this effect by excretion of anti-microbial components, by competing with pathogens for intestinal nutrients and/or mucosal adhesion sites or modulating the immune system.
A parallel, double-blind, placebo-controlled 4-week intervention was performed in healthy males, to study the effect of a blend of probiotic bacteria (Lactobacillus helveticus Rosell-52, Lactobacillus rhamnosus Rosell-11, Bifidobacterium longum ssp. longum Rosell-175) and a probiotic yeast (Saccharomyces cerevisiae var boulardii CNCM I-1079) on enterotoxigenic Escherichia coli (ETEC) challenge. Primary outcomes studied were fecal ETEC excretion and total fecal output per day.
Subjects were randomized to the probiotic (5 × 109 colony-forming units (CFUs); twice daily; n=30) or placebo group (twice daily; n=30). After 2 weeks, subjects were orally challenged with a live attenuated ETEC (3 × 109 CFU), previously demonstrated to induce mild, short-lived symptoms of a foodborne infection. Before and after ETEC challenge, subjects collected 24 h fecal samples. Compliance to study guidelines, stool consistency (Bristol Stool Score), stool frequency, and frequency and severity of gastrointestinal (GI) complaints were recorded by the subjects on a Daily Record Questionnaire.
ETEC challenge induced a significant increase in fecal ETEC excretion in both groups. However, a statistically significant increase in fecal output was only observed in the probiotic group. ETEC challenge resulted in a decrease in the percentage of fecal dry weight, and an increase in reported Bristol Stool Score, stool frequency and GI complaints. Dietary probiotics significantly decreased the percentage of fecal dry weight. In addition, ETEC increased C-reactive protein, total secretory Immunoglobulin A (IgA) and Immunoglobulin G Colonization Factor Antigen II.
Dietary probiotics did not increase resistance to oral attenuated ETEC challenge in human subjects.
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E Lucas, R Holleman, J Hoolwerf and S van Schalkwijk (NIZO Food Research, Ede, the Netherlands) are thanked for their support of study logistics, and assistance with laboratory analyses. M Kleerebezem (NIZO Food Research, Ede, the Netherlands) is thanked for critically reviewing the manuscript and E Alhoniemi (Pharmatest, Finland) is thanked for performing the statistical analysis. The study was funded by Lallemand Health Solutions Inc., Montreal, Canada.
All authors have read and approved the final manuscript. SB, RB and TT designed the study. SB and EF conducted the study and analyzed the data. SB, SG, TT and RB wrote the paper. SB and TT had primary responsibility for final content.
About this article
The sponsor was involved in the design of the study, interpretation of the data and writing of the manuscript. No external funding, apart from the authors’ institutions, was available for this study.
The trial was registered on ClinicalTrials.gov, NCT01709266.
Supplementary Information accompanies this paper on European Journal of Clinical Nutrition website (http://www.nature.com/ejcn)