Impact of Bifidobacterium animalis subsp. lactis BB-12 and, Lactobacillus acidophilus LA-5-containing yoghurt, on fecal bacterial counts of healthy adults

Abstract

This randomized, placebo-controlled, double blind, parallel dose–response study investigated the impact of 4-week commercial yoghurt consumption supplemented with Bifidobacterium animalis subsp. lactis (BB-12) and Lactobacillus acidophilus (LA-5) on fecal bacterial counts of healthy adults. Fifty-eight volunteers were randomly assigned to three different groups: 1. placebo (no probiotic, no starter and no green tea extract); 2. Yoptimal (10⁹ cfu/100 g of BB-12 and LA-5 and 40 mg of green tea extract) and 3. Yoptimal-10 (10¹⁰ cfu/100 g of BB-12, 10⁹ cfu/100 g of LA-5 and 40 mg of green tea extract). These yoghurt products also contained Lactobacillus delbrueckii subsp. bulgaricus (10⁷ cfu/100 g) and Streptococcus thermophilus (10¹⁰ cfu/100 g). The quantitative PCR (qPCR) results showed that there were significant increases (P = 0.02) in bifidobacteria counts with the Yoptimal treatment as compared to baseline. The fecal numbers of B. animalis subsp. lactis and LA-5 significantly increased in the two probiotic treatments compared to the placebo treatment. Viable counts of fecal lactobacilli were significantly higher (P = 0.05) and those of enterococci were significantly lower (P = 0.04) after the intervention when compared to placebo. No significant difference was observed between treatments in volunteers' weight, waist girth, blood pressure, fasting plasma triglyceride and HDL-C concentrations, as well as cholesterol/HDL-cholesterol ratio. However, a significant increase in plasma cholesterol levels was observed in the placebo group (P = 0.0018) but the levels remained stable in the two probiotic yoghurt groups. These results show that probiotic strains supplemented in the form of yoghurt remain active during gut transit and are associated with an increase in beneficial bacteria and a reduction in potentially pathogenic bacteria. This trial was registered at clinicaltrials.gov as NCT00730626.

Introduction

The FAO/WHO defines probiotics as follows: “Live microorganisms, which, when administered in adequate amounts, confer a health benefit on the host” (Araya et al., 2002). Accordingly, probiotic bacteria contained in commercial products should retain the functional and health-beneficial characteristics for which they were originally selected. These include the growth and survival of the organisms during product production, storage, and post-consumption during the transit from stomach to intestine (Tuomola et al., 2001). The dose of the ingested probiotic is an important factor that will impact the concentration found in the various parts of the gastrointestinal (GI) tract. In Canada, the level of probiotic strain in a serving of a stated size of the food has to be declared and that serving should contain a minimum of 1.0 × 10⁹ cfu of one of the probiotic bacteria eligible for non-specific health claims (Guidance Document — The Use of Probiotic Microorganisms in Food. Food Directorate, Health Products and Food Branch, Health Canada, April 2009).

In healthy individuals, the consumption of probiotic products containing beneficial bacteria, such as bifidobacteria and lactobacilli, can result in physiological benefits. Probiotics play a major role in maintaining the equilibrium and stability of the enteric microbiota, which aids gastrointestinal functions, including control transit time, bowel habits, control of nutrient bioavailability and modulation of gastrointestinal immune activity (Delcenserie et al., 2008, Sanders et al., 2007). Probiotics may also minimize disturbances of the intestinal microbiota following antibiotic treatment. Balance and stability of the microbial community structure can be achieved through increased levels of lactobacilli and bifidobacteria, preferably at the expense of more harmful bacteria (Fooks and Gibson, 2002).

Human trials are encouraged by FAO/WHO in their guidelines for the evaluation of probiotics in food (Araya et al., 2002). In addition, the Canadian Food Inspection Agency (CFIA) revised the Chapter 8 — Health Claims — of the Guide to Food Labelling and Advertising in order to protect consumers by ensuring that claims regarding probiotics are accurate and in compliance with the Guide. Two types of health claims can be made: non-strain-specific claim and, strain-specific claims in which the health benefits or effects of specific strains of probiotics are described. Few well-designed human clinical trials have studied the microbiological effects of yoghurt containing specific strains of probiotic bacteria (Collado et al., 2006, Guerin-Danan et al., 1998, Mättö et al., 2006, Yamano et al., 2006). In this type of study, it is important to determine what doses can reinforce bifidobacteria or lactobacilli populations without altering the balanced microbial ecosystem of healthy individuals (Larsen et al., 2006).

The aim of this randomized, double-blind, placebo-controlled intervention study was to quantify changes from baseline in Lactobacillus acidophilus LA-5 and Bifidobacterium animalis subsp. lactis BB-12 fecal numbers (primary outcome) after daily consumption, for a period of 4 weeks, of a probiotic yoghurt, using quantitative PCR (qPCR). The impact on fecal bacterial counts was also verified through traditional culturing. Some authors have suggested that the production of short chain fatty acids by probiotics in the gut may lead to alterations in blood lipids (Pereira and Gibson, 2002). Others have observed that probiotics may assimilate cholesterol directly from the GI or bile salts, thereby hampering cholesterol absorption (Gilliland et al., 1985, Tahri et al., 1996). Although promising, these data need further confirmation from clinical studies in human subjects. Thus, one of the secondary objectives of the present study was also to investigate the impact of the probiotic yoghurt products on plasma lipid concentrations.