The worldwide emergence of bacterial resistance to antibacterial agents has produced a need for new methods of combating bacterial infections. This need is forced on us by the long time lag in developing new antibacterial agents. Even though new agents may be in the pipeline, they will not solve all current resistance problems. In addition, we also have to recognise that the use of antibacterial agents not only targets resistant bacteria but also disturbs normal human flora, which may itself further inhibit our defence against infection. Bacteriotherapy, as an alternative, has been shown effective in preventing and treating certain infections of bacterial, viral and fungal origin. Fecal microbiota transplantation (FMT) is the administration of a solution of fecal matter from a donor into the intestinal tract of a recipient in order to directly change the recipient’s microbial composition and confer a health benefit. Borody and colleagues used FMT to treat 6 patients with refractory ulcerative colitis and follow up at 1–13 years post-FMT showed no clinical evidence of ulcerative colitis [4]. Similarly, Duplessis et al. utilized FMT to treat a patient with severe Crohn's disease complicated by refractory CDI [5]. Obesity is another condition that could potentially benefit from FMT. FMT from lean to obese individuals led to increased insulin sensitivity in the patients compared to the control group [6].

Gut microbiome is becoming more important in the realm of cancer immunotherapy. Waves of clinical trials have been initiated to examine the clinical outcomes of modulating gut microbiota in the context of cancer therapy [7].

However, it remains challenging for bacteriotherapy to be adopted into clinical practice at this stage as little is known about its mechanism of action on modulating the immunity during cancer treatment. The proposed mechanisms by which bacteria act as anti-cancer agents have been studied and proposed to be either through enhancing human immunity, activating inflammasome pathways, CD4, CD25 and CD8 anti-tumor effectors T cell responses, TNF-α innate immune system in bacteria-based tumor necrosis, through released substances (such as bacteriocins, biosurfactants, phenazine 1,6-di-carboxylic acid). They also act as a carrier for cancer therapeutic agents and bacteria-based microrobot (Bacteriobot) [8].

The intestinal microbiota play a relevant role in disorders of the nervous system. The microbiota–gut– brain axis may represent a new target in the prevention and treatment of neuropsychiatric disorders. Analyses of the available research results have shown that selected bacteria affect the gut–brain axis in healthy people and people with selected diseases i.e., Alzheimer’s disease, Parkinson’s disease, depression, and autism spectrum disorders and hence acquired the term “Psychobiotics” [9].

In conclusion, bacteriotherapy is an old-modern concept in the field of therapeutics showing promising findings. Bacteriotherapy is a rich field for conducting clinical research and investigations taking into consideration its potential adverse effects in the future work. Keywords : Probiotics, fecal microbiota transplantation, dysbiosis, microbiota