Sources, isolation, characterisation and evaluation of probiotics.

According to the FAO and the WHO, probiotics are 'live microorganisms which, when administered in adequate amounts, confer a health benefit on the host'. The strains most frequently used as probiotics include lactic acid bacteria and bifidobacteria, which are isolated from traditional fermented products and the gut, faeces and breast milk of human subjects. The identification of microorganisms is the first step in the selection of potential probiotics. The present techniques, including genetic fingerprinting, gene sequencing, oligonucleotide probes and specific primer selection, discriminate closely related bacteria with varying degrees of success. Additional molecular methods, such as denaturing gradient gel electrophoresis/temperature gradient gel electrophoresis and fluorescence in situ hybridisation, are employed to identify and characterise probiotics. The ability to examine fully sequenced genomes has accelerated the application of genetic approaches to the elucidation of the functional roles of probiotics. One of the best-demonstrated clinical benefits of probiotics is the prevention and treatment of acute and antibiotic-associated diarrhoea;however, there is mounting evidence for a potential role for probiotics in the treatment of allergies and intestinal, liver and metabolic diseases. There are various mechanisms by which probiotics exert their beneficial effects: regulation of intestinal permeability, normalisation of host intestinal microbiota, improvement of gut immune barrier function, and adjustment between pro- and anti-inflammatory cytokines. The number of studies carried out to test the effects of probiotics in vitro and in animals is enormous. However, the most reliable method of assessing the therapeutic benefits of any probiotic strain is the use of randomised, placebo-controlled trials, which are reviewed in this article [corrected].