The potential mechanisms involved in the anti-carcinogenic action of probiotics

Probiotic bacteria are live microbial food ingredients that provide a health benefit to the consumer. In the past it was suggested that they served to benefit the host primarily through the prevention of intestinal infections. More recent studies have implicated probiotic bacteria in a number of other beneficial effects within the host including: *The suppression of allergies. *Control of blood cholesterol levels. *Modulation of immune function. *And the prevention of cancers of the colon. The reputed anti-carcinogenic effect of probiotics arises from in vivo studies in both animals and to a limited extent in man; this evidence is supported by in vitro studies with carcinoma cell lines and anti-mutagenicity assays. However, the mechanisms involved in any effect have thus far been difficult to elucidate; studies offer evidence for a variety of mechanisms; we have reviewed these and come to the opinion that, the anti-carcinogenic effect may not be attributable to a single mechanism but rather to a combination of events not yet fully elucidated or understood.

Antigenotoxicity of probiotics and prebiotics on faecal water-induced DNA damage in human colon adenocarcinoma cells

Six strains of lactic acid producing bacteria (LAB) were incubated (1 x 10(8)cfu/ml) with genotoxic faecal water from a human subject. HT29 human adenocarcinoma cells were then challenged with the resultant samples and DNA damage measured using the single cell gel electrophoresis (comet) assay. The LAB strains investigated were Bifidobacterium sp. 420, Bifidobacterium Bb12, Lactobacillus plantarum, Streptococcus thermophilus, Lactobacillus bulgaricus and Enterococcus faecium. DNA damage was significantly decreased by all bacteria used with the exception of Strep. thermophilus. Bif. Bb12 and Lact. plantarum showed the greatest protective effect against DNA damage. Incubation of faecal water with different concentrations of Bif. Bb12 and Lact. plantarum revealed that the decrease in genotoxicity was related to cell density. Non-viable (heat treated) probiotic cells had no effect on faecal water genotoxicity. In a second study, HT29 cells were cultured in the presence of supernatants of incubations of probiotics with various carbohydrates including known prebiotics; the HT29 cells were then exposed to faecal water. Overall, incubations involving Lact. plantarum with the fructooligosaccharide (FOS)-based prebiotics Inulin, Raftiline, Raftilose and Actilight were the most effective in increasing the cellular resistance to faecal water genotoxicity, whereas fermentations with Elixor (a galactooligosaccharide) and Fibersol (a maltodextrin) were less effective. Substantial reductions in faecal water-induced DNA damage were also seen with supernatants from incubation of prebiotics with Bif. Bb12. The supernatant of fermentations involving Ent. faecium and Bif. sp. 420 generally had less potent effects on genotoxicity although some reductions with Raftiline and Elixor fermentations were apparent.

In vitro evaluation of the antimicrobial activity of a range of probiotics against pathogens: Evidence for the effects of organic acids

The aim of this study was to investigate the antimicrobial properties of fifteen selected strains belonging to the Lactobacillus, Bifidobacterium, Lactococcus, Streptococcus and Bacillus genera against Gram-positive and Gram-negative pathogenic bacteria. In vitro antibacterial activity was initially investigated by an agar spot method. Results from the agar spot test showed that most of the selected strains were able to produce active compounds on solid media with antagonistic properties against Salmonella Typhimurium, Escherichia coli, Enterococcus faecalis, Staphylococcus aureus and Clostridium difficile. These results were also confirmed when cell-free culture supernatants (CFCS) from the putative probiotics were used in an agar well diffusion assay. Neutralization of the culture supernatants with alkali reduced the antagonistic effects. These experiments are able to confirm the capacity of potential probiotics to inhibit selected pathogens. One of the main inhibitory mechanisms may result from the production of organic acids from glucose fermentation and consequent lowering of culture pH. This observation was confirmed when the profile of organic acids was analysed demonstrating that lactic and acetic acid were the principal end products of probiotic metabolism. Furthermore, the assessment of the haemolytic activity and the susceptibility of the strains to the most commonly used antimicrobials, considered as basic safety aspects, were also studied. The observed antimicrobial activity was mainly genus-specific, additionally significant differences could be observed among species.

Comparative in vitro inhibition of urinary tract pathogens by single- and multi-strain probiotics

PURPOSE: Multi-species probiotic preparations have been suggested as having a wide spectrum of application, although few studies have compared their efficacy with that of individual component strains at equal concentrations. We therefore tested the ability of 4 single probiotics and 4 probiotic mixtures to inhibit the urinary tract pathogens Escherichia coli NCTC 9001 and Enterococcus faecalis NCTC 00775. METHODS: We used an agar spot test to test the ability of viable cells to inhibit pathogens, while a broth inhibition assay was used to assess inhibition by cell-free probiotic supernatants in both pH-neutralised and non-neutralised forms. RESULTS: In the agar spot test, all probiotic treatments showed inhibition, L. acidophilus was the most inhibitory single strain against E. faecalis, L. fermentum the most inhibitory against E. coli. A commercially available mixture of 14 strains (Bio-Kult(®)) was the most effective mixture, against E. faecalis, the 3-lactobacillus mixture the most inhibitory against E. coli. Mixtures were not significantly more inhibitory than single strains. In the broth inhibition assays, all probiotic supernatants inhibited both pathogens when pH was not controlled, with only 2 treatments causing inhibition at a neutral pH. CONCLUSIONS: Both viable cells of probiotics and supernatants of probiotic cultures were able to inhibit growth of two urinary tract pathogens. Probiotic mixtures prevented the growth of urinary tract pathogens but were not significantly more inhibitory than single strains. Probiotics appear to produce metabolites that are inhibitory towards urinary tract pathogens. Probiotics display potential to reduce the incidence of urinary tract infections via inhibition of colonisation.

Immunosenescence and the gut microbiota: the role of probiotics and prebiotics

The global population is becoming increasingly older presenting medical and economic challenges to society. One factor associated with the aging process is immunosenescence, which may be defined as the decline in immunity with age, and represents a potential causative factor for many age related illnesses. The profile of the gut microbiota is also known to alter with aging and these changes have been linked the declines in the immunity observed in immunosenescence. For example, above the age of 60 years populations of bifidobacteria have been observed to decrease markedly, leading to a reduction in the inhibition of the growth of some pathogens and potentially an increase in the susceptibility to infections. As such, an interest exists in attempting to reverse their decline in elderly individuals, through the use of both probiotics and prebiotics. Both approaches have shown to be encouraging in altering microbiota profiles beneficially and in reducing immunosenescence by reducing the colonisation potential of pathogens and counteracting chronic inflammation. The current review will give an overview of the process of immunosenescence and its role in disease, detail how the microbiota are involved in its progression and highlight data suggesting that pre- and probiotics may counteract these age-related events.

Impact of probiotics, prebiotics and synbiotics on lipid metabolism in humans

Public health strategies for reducing the risk of coronary heart disease have focused on lowering plasma lipids, particularly cholesterol levels, with recent studies also highlighting triacylglycerol (TAG) as an important modifiable risk factor. One approach is to supplement the diet with probiotics, prebiotics or synbiotics. Probiotics are live microorganisms which when administered in adequate amounts confer a health benefit on the host. Putative health benefits include improved resistance to gastrointestinal infections, reduction in lipid levels and stimulation of the immune system. Prebiotics are selectively fermented dietary components that are aimed at improving host health through selective fermentation by the gut microbiota, such as bifidobacteria and lactobacilli. Animal studies have shown prebiotics to markedly reduce circulating TAG and to a lesser extent cholesterol concentrations, with favourable but inconsistent findings with respect to changes in lipid levels in human studies. Here we provide an overview of the effects, and possible mechanisms, of probiotics, prebiotics and synbiotics (combination of a probiotic and prebiotic) on circulating lipeamia in humans.

Antipathogenic activity of probiotics against Salmonella Typhimurium and Clostridium difficile in anaerobic batch culture systems: is it due to synergies in probiotic mixtures or the specificity of single strains?

Probiotics are currently being investigated for prevention of infections caused by enteric pathogens. The aim of this in vitro study was to evaluate the influence of three single probiotics: Lactobacillus casei NCIMB 30185 (PXN 37), Lactobacillus acidophilus NCIMB 30184 (PXN 35), Bifidobacterium breve NCIMB 30180 (PXN 25) and a probiotic mixture containing the above strains plus twelve other strains belonging to the Lactobacillus, Bifidobacterium, Lactococcus, Streptococcus and Bacillus genera on the survival of Salmonella Typhimurium and Clostridium difficile using pH-controlled anaerobic batch cultures containing mixed fecal bacteria. Changes in relevant bacterial groups and effects of probiotic addition on survival of the two pathogens were assessed over 24 h. Quantitative analysis of bacterial populations revealed that there was a significant increase in lactobacilli and/or bifidobacteria numbers, depending on probiotic addition, compared with the control (no added probiotic). There was also a significant reduction in S. Typhimurium and C. difficile numbers in the presence of certain probiotics compared with controls. Of the probiotic treatments, two single strains namely L. casei NCIMB 30185 (PXN 37), and B. breve NCIMB 30180 (PXN 25) were the most potent in reducing the numbers of S. Typhimurium and C. difficile. In addition, the supplementation with probiotics into the systems influenced some fermentations parameters. Acetate was found in the largest concentrations in all vessels and lactate and formate were generally detected in higher amounts in vessels with probiotic addition compared to controls.