Michelle Fleet and Pattanathu K.S.M. Rahman*
School of Science and Engineering, Teesside University, Middlesbrough, UK
*Corresponding author e‐mail: p.rahman@tees.ac.uk
With growing interest in the use of probiotics for maintaining good health, we have examined the far‐reaching scope of their potential use. Research surrounding probiotics has developed at a rapid pace and has continued to be of great interest to consumers and scientists over recent years. While some reservations regarding their efficacy are consistently raised with emerging research, we examine these issues and discuss their implications. Recent advances in the area and how such developments may be utilized to facilitate further advancement are described. Potential barriers to interpreting current clinical data are discussed, as is the possible future direction of suitable experimental design. For the purposes of this review, the legislative issues surrounding the manufacturing of probiotics have not been covered. While there is ongoing interesting research in the field of probiotics, examining strain‐specific activity, enumeration, robust human trials and the mechanisms of action of probiotics will provide us with a great deal of information. Traditional analytical chemistry methods, advances in metagenomics and culturing techniques for gut bacteria should serve as key tools in the research and development of probiotics for the food and pharmaceutical industries. In the interests of public health, a co‐ordinated, multifaceted, and multidisciplinary approach is required to give full assurance about the health benefits to human subjects of probiotics, administered at specific doses and defined to strain level.
Over recent years, we have heard more and more about probiotics and their health benefits. Our knowledge of both microbiology and nutrition has developed dramatically since their health benefits were initially recognized. For thousands of years before we were aware of their benefits, people were consuming fermented foods containing micro‐organisms.
In recent times, there has been ever‐increasing interest in the so‐called “friendly bacteria.” To quote some figures, a Science Direct database search of the word “probiotic” has shown an increase to 2187 publications, just under 400 more than in 2013. This has come a long way since 1999, when only 192 papers were added to the database. In 2013, 115 newspaper articles contained the word “probiotic” in comparison with just 10 in a 1999 News Bank search. Looking at consumer demand, Mintel research conducted in July 2014 discovered that two in five of those who drink probiotic yoghurt do so because of digestive health.
Probiotics are non‐pathogenic live active micro‐organisms which improve microbial balance, particularly in the gastrointestinal (GI) system. Health benefits are provided to the host when consumed in specific quantities and are believed to be largely strain specific (Butel 2014). Typical probiotics in use are lactobacilli (L. acidophilus, L. casei, L. fermentum, L. gasseri, L. johnsonii, L. paracasei, L. plantarum, L. rhamnosus, and L. salivarius) and bifidobacteria (B. adolescentis, B. animalis, B. bifidum, B. breve, and B. longum). The aforementioned species, when presented in food at a level of 1 × 109 colony forming units (CFU) per serving, have been accepted by Health Canada (2009) to be given the term “probiotic” for which non‐strain‐specific claims might be made. The general benefit of supporting a healthy gut microbiota is a core benefit of probiotics as considered by Canadian regulatory authorities; these represent well‐researched species, likely to impart some health benefit (Hill et al. 2014). Other genera for which health benefits have been documented (Fijan et al. 2014) are strains of Saccharomyces, Enterococcus, Streptococcus, Pediococcus, Leuconostoc, Bacillus, and Escherichia coli.
The proposed health benefits of probiotics are wide‐ranging and research is continuing to establish a comprehensive picture of the microbiota, host cells, and nutrients which interact with one another. The mechanisms by which probiotics operate are only just beginning to be understood. Butel (2014) reports that research in relation to mechanisms has been conducted largely in vitro or on animal models. As subsequent interpretation of their extensive value to human subjects may be met with a degree of caution, we anticipate there will be further research in this area following careful examination of the applicable ethical issues. In addition to attempting to modulate the gut microbiota for preventive purposes, research has focused on the feasibility of treating diseases with probiotics. The Royal Pharmaceutical Society (2013a) applauds the recognition of the need for research into use of non‐antibiotic infection management techniques, which include probiotics. In terms of prescription as a pharmaceutical agent, a combination of various probiotics proved to be more efficacious than single strains for prophylactic activities (Sarker 2013).
This review will focus on the present view of scientific research in the area of probiotics and reflect upon current issues which need further examination. Magrone and Jirillo (2013) identified the three main activities of probiotics: immune regulation through microbial activity; alteration of the microbiota; and prevention of bacterial infection.
A “healthy” intestine has been described by Amara and Shilb (2015) as one which contains a balance of lactobacilli, streptococci, Clostridia, coliform bacteria, and Bacterioides. It is an imbalance or dysbiosis which is often implicated in various health problems. A range of factors have been identified which may influence this balance, from modern diet, lifestyle, and environment (Sun and Chang 2014) to therapeutic disruption factors (antibiotics, probiotics, prebiotics/dietary intervention, and fecal transplantation) identified by Walker and Lawley (2013). The influence of the mother in the case of infants has also been recognized by Chassard et al. (2014), who state that the infant microbiome is partly inherited from the mother and the environment during the first 2 years of life. The majority of research has focused on the large intestine and fecal microbiota, but the significance of the small intestine is becoming apparent, with recent work completed by El Aidy et al. (2014).
Probiotics have been indicated in a number of GI conditions including irritable bowel disease (IBD) and, more recently, irritable bowel syndrome (IBS) by Shanahan and Quigley (2014). A 2014 mini‐review by Sherban suggests that although there is an ample body of evidence that gut microbiota contributes to GI tumorigenesis, there is not enough evidence from human studies to strongly support the use of these biotherapeutics in prevention/therapy of GI cancers.
In a clinical setting, we have seen the use of probiotics in the treatment and prevention of diarrhea, in children (Wanke and Szajewska 2014) and patients undergoing radiotherapy (Demersa et al. 2014). Clostridium difficile infection is more likely to occur in the elderly and sick and can occur following antibiotic treatment. Furthermore, it can lead to more serious infections of the intestines with severe inflammation of the bowel (pseudomembranous colitis). Tojo et al. (2014) suggest that treatment with probiotics for C. difficile infections has an “undoubtedly proven role.” Lenoir‐Wijnkoop et al. (2014) concluded that use of a fermented milk dairy product containing L. paracasei CNCM I‐1518 to prevent antibiotic‐associated diarrhea (ADD) in older hospitalized patients could lead to substantial cost savings. Public Health England (PHE) (2013) states that it cannot at present recommend the use of probiotics for the prevention of AAD or C. difficile infection. The Royal Pharmaceutical Society (2013b) concludes that evidence is of moderate quality but consistently shows that probiotics prevent C. difficile‐associated diarrhea and are safe. In its Clinical Knowledge Summary, NICE (2013a) reiterates PHE’s position due to insufficient evidence about the treatment and prevention of C. difficile with probiotics.
In terms of preventing or treating AAD, NICE (2013b) offers no formal guidance on the use of probiotics and suggets that future studies should address factors such as strains or blends of probiotics, patient characteristics, and type of antibiotic. In contrast, the Royal College of Nursing (RCN 2013), in its guidance to nursing staff, advises on the consumption of yoghurt drinks containing probiotics to reduce the length of a diarrhea episode.
Although there is no universally accepted term for a functional food (McKevith 2013), there is a loose definition of a food that has disease‐preventing properties over and above its usual nutritional value and/or which has health‐promoting benefits.
The British Nutrition Foundation (BNF 2014) states that although functional foods and drinks may provide benefits in health terms, they should not be seen as an alternative to a varied and balanced diet and a healthy lifestyle. This echoes the position of Adam et al. (2012), who state that probiotics should not be treated as an “elixir of life” but as part of a balanced diet. As shown in Table 11.1, the products available are milk and dairy products and, with the exception of a yoghurt produced by a family dairy, are made by large multinational companies.
Table 11.1 Probiotic dairy products available in supermarkets in the UK. Supermarket own brands are not included.
| Brand | Product | Presentation | Volume | Probiotic | Amount |
| Danone | Actimel® | Yoghurt drink | 100 g | Lactobacillus casei DN‐114001 (Brand name: Danone) | Minimum 10 billion |
| Activia® | Yoghurt | 125 g | B. lactis DN 173010 (Brand name: ActiRegularis) | 4 billion | |
| Lancashire Farm | Bio‐yoghurt | Yoghurt | 500 g/1 Kg | Bifidobacterium BB12®, Lactobacillus acidophilus | Not known |
| Yakult | Yakult® | Fermented milk drink | 65 mL | Lactobacillus casei Shirota | Minimum 6.5 billion |
| Müller | Vitality® | Yoghurt drink | 100 g | Bifidobacterium BB12® | Not known |
| Yoghurt | 120 g | Not known |
The use of comparative genomics and genome sequencing of probiotic bacteria is expected to become a “gold standard” method for characterization and typing of isolates (Bull 2013). DairyCo (2013) informs us that food is developing towards nutritional or functional needs in developed countries, so we expect to see some interesting changes to the current UK probiotic market in coming years. As an example of recent innovation, Ganeden Biotech US (2015) introduced single serving disposable coffee K‐cups containing probiotics; this is patented and defined to strain level with Food and Drug Administration (FDA) Generally Recognized as Safe (GRAS) status. As more and more consumers ask about the benefits of such products, it is the role of health professionals, especially state registered dieticians, to provide appropriate advice and guidance within the remit of their professional practice.
Since the effects of probiotics are determined largely by their specific type, sometimes down to strain level, their value is often considered in terms of use by practitioners. For example, in an expert review, Boyonova and Mitov (2012) concluded that further studies evaluating strain selection by molecular methods will reveal the full potential of probiotics as an adjunct to antibiotic therapy for co‐administration.
A recent review by Bron et al. (2013) identified that in order to optimize strain selection for specific interventions and maximize the efficacy of probiotics, a more precise understanding of the molecular mechanisms by which probiotic effector molecules elicit host immune responses is essential. Focusing on the genus Lactobacillus, the advantages of determining this information were cited by these authors as follows.
Most interesting was the possibility that the probiotic‐derived effector molecules may have an application as bioactives administered in a non‐viable form. In a later review by Ruiz et al. (2014), this was explored further, and it was concluded that such isolated metabolites or molecules may offer an alternative treatment in inflammatory disorders.
In a systematic review by Bermudez‐Brito et al. (2012), to explore probiotic modes of action focusing on how gut microbes influence the host, the authors concluded that experiments on different intestinal epithelial cells require careful interpretation due to the fact that different cell lines vary in their characteristics. Bron et al. (2013) look towards future human studies in order to fill the gap between preclinical research and large efficacy clinical trials. If we take a proactive and pre‐emptive approach to possible challenges in terms of their subsequent future application in the food and pharmaceutical industries, this will be most beneficial to public health and assist in achieving the goals identified by Bermudez‐Brito et al. (2012) of fostering the development of novel strategies for the treatment or prevention of gastrointestinal and autoimmune diseases, in addition to improving the credibility of the probiotic concept.
As knowledge is rapidly advancing in the field of metagenomics, we can expect to see interesting developments in terms of understanding the gut microbiota and probiotic use. In a recent review by Walker et al. (2014), the continual need for microbial cultivation in addition to metagenomics was highlighted. It was concluded that metagenomics and culturing can provide further insight and essentially serve to complement each other. An outstanding question the authors posed was whether many important new microbial isolates could be obtained simply by varying substrates and nutrients in anaerobic growth media. This would lead to an interesting avenue of research, since it would allow us to predict changes to gut bacteria diversity if conditions were manipulated. Moreover, it has been recommended to employ a combination of phenotypic and genetic techniques to accomplish the identification, classification, and typing of micro‐organisms (Adam et al. 2012). If this is achieved, we can expand our knowledge of the behavior of probiotic strains and applications in both maintaining optimum health condition and the potential for treating specific disease.
Regarding the above discussion about a complementary approach to metagenomics and culturing, we must also consider the point that it is culture‐independent techniques which can enumerate probiotic cells, since cell culture estimates only the replicating strains and not those in the viable but non‐culturable (VBNC state. By a culture‐independent technique, we mean fluorescent in situ hybridization, nucleic acid amplification techniques such as real‐time quantitative PCR, reverse transcriptase PCR, propidium monoazide PCR, and cell sorting techniques such as flow cytometry/fluorescent activated cell sorting. The dose of required probiotic is an important factor when critically evaluating any study or considering its potential use in a clinical setting. Davis (2014) recommends these methods to enumerate VBNC bacteria and culturable bacteria and also calls for a more holistic definition of viable probiotic bacteria. Future research will hopefully be able to more carefully examine this issue and fine‐tune this interpretation of viable cells in accordance with evolving techniques.
In a comprehensive literature review (1985–2013), McFarland (2014) echoed previous work in concluding that future trials should include a description of the probiotic down to strain level. Different molecular microbiological typing techniques can be applied such as pulsed‐field gel electrophoresis, amplified fragment length polymorphism or multilocus sequence typing (Rijkers 2011). Linking this with industrial developments, Nestlé have sequenced several probiotic genomes (2014) and ongoing partnerships between researchers and manufacturers will undoubtedly give rise to diversification of products.
Novel and interesting developments have been seen within analytical chemistry, particularlythe use of high performance liquid chromatography (HPLC) when researching probiotics. For example, Mogna et al. (2014) stated the possible hypothesis that the administration of selected oxalate‐degrading probiotics could be an alternative approach to reducing the intestinal absorption of oxalate and the resulting urinary excretion. The methodology included testing oxalate‐degrading activity of 13 lactobacilli and five bifidobacteria using a novel reverse‐phase (rp) HPLC method.
Similarly, in a study by Dubey et al. (2012), the biohydrogenation of unsaturated linoleic acid to its conjugated form by Pediococcus spp. GS4 was measured using UV scanning rp‐HPLC and gas chromatography‐mass spectrometry. HPLC has also been used to analyze folate compounds produced by strains of bifidobacteria, concluding that some may contribute to folate intake (d’Aimmo et al. 2012). The investigation of oligosaccharide utilization of probiotic strains was recently examined by Sims et al. (2014) using high performance anion exchange chromatography and HPLC and it was found that strains utilized them differently.
We can therefore foresee the increasing use of these techniques in probiotic research to determine the specific phenotypical traits of strains of bacteria. This in turn can lead to further studies which could determine their possible use and required dosage.
If Italy is successful in obtaining permission to use “probiotic” as a generic term on its food labeling, the UK could also do this, getting an extension as a “concerned Member State” (Pendrous 2014). This could have interesting consequences for the food industry since it would pave the way for simple labeling and subsequent ease of consumer recognition.
The need for more comprehensive research in this area cannot be stressed enough. There are currently 54 clinical trials being conducted within the NHS (2014), showing the potential of probiotics in a wide range of treatment areas. However, unlike several other nutritional issues (Public Health England 2014), there is no government Scientific Advisory Committee for probiotics. Additionally, NICE guidelines in which probiotics are mentioned, as shown in Table 11.2, are meager in relation to the range of conditions they cover.
Table 11.2 NICE guidelines in which probiotics are mentioned.
| Condition | Name and date of NICE Clinical Guideline (CG) | Guidance on probiotic use | Status |
| Otitis media with effusion (OME) in children | CG60 February 2008 | Dietary modification, including probiotics not recommended | Last reviewed August 2011 Next review date to be confirmed Placed on static list February 2014 |
| Diarrhoea and vomiting in children | CG84 April 2009 | Highlights methodological limitations of studies, treatment regimens used and variation in the specific probiotics evaluated. Also states many studies completed in developing countries, where response to probiotics may differ. Good‐quality randomized controlled trials should be conducted in the UK to evaluate the effectiveness and safety of specific probiotics, using clearly defined treatment regimens and outcome measures | Placed on static list 2014 Review date to be confirmed |
| Irritable bowel syndrome (IBS) in adults | CG61 February 2008 | States “People with IBS who choose to try probiotics should be advised to take the product for at least 4 weeks while monitoring the effect. Probiotics should be taken at the dose recommended by the manufacturer” | This evidence has not been reviewed since 2008. Placed on static list December 2013 Clinical Guidance updated on April 2017 Next review: 2019 |
With little comprehensive guidance from NICE and no government scientific advisory committee for probiotics, there is a potential vacuum in terms of professional knowledge dissemination within the UK. Furthermore, the use and promotion of probiotics by health professionals are likely to remain limited until these important steps are taken.
There are several issues which we have identified in this review which, if adequately addressed, could assist our advancement in this field tremendously. Since in vitro culture conditions may influence the expression of certain molecular characteristics, and results obtained in animal models cannot be directly transferred to humans due to physiological differences (Bermudez‐Brito et al. 2012), robust, well‐designed and reproducible clinical trials on human subjects, with a tightly defined description of both strain and viable cells, would secure confidence and assist in making the vital transition into clinical practice. With the rapidly emerging techniques and knowledge to allow us to understand the bacteria within our bodies, the effectiveness of specific probiotic strains at accurate doses is a key consideration for industry, regulators, and health professionals alike.