Probiotics are defined as non-pathogenic live microorganisms that, when administered in adequate amounts, confer health benefits on the host. Association of probiotics with human beings has a lot of history. Well known as 'health-friendly bacteria', they are widely used commercially as a functional food. The popularity of probiotics has gone exponentially high due to an increasing number of clinical trials, supporting their beneficial effects. Several in vivo and in-vitro experimental evidence supports strain-specific and disease-specific probiotic efficacy to prevent and ameliorate antibiotic-associated diarrhoea, traveller's diarrhoea, ulcerative colitis, and many more. Besides, numerous recent studies have reported that probiotics could have a significant effect in alleviating various metabolic, lifestyle and diet-related disorders like obesity, type 2 diabetes, metabolic syndrome, irritable bowel syndrome Strains of Bifidobacterium, Lactobacillus and Saccharomyces boulardii are the most commonly used as probiotics. Safety, efficacy, pathogenicity, infectivity, intrinsic property, virulence factors are to be addressed during probiotic selection. The underlying mechanisms of probiotics effects are still not fully elucidated and have been under intensive research. Numerous diverse, strain-specific probiotic mechanisms have been proposed, which include early colonization of perturbed microbes, competitive exclusion of pathogens, short-chain volatile fatty acid production, alteration of gut pH, immunomodulation and many more. Considering the remarkable influence on human health, probiotics seem to be alluring attractive agents to promote human health conditions and to improve the quality of life against several diseases. This review discusses the current documentation and recent advances on probiotics and their possible health attributes, in scientific literature, focusing on diverse, heterogeneous, and strain-specific mechanisms of action. Randomised human controlled clinical trials are needed to reconfirm its safety and beneficial effects.
