Probiotics, living non-pathogenic microorganisms, can significantly benefit the host by enhancing microbial balance in the gut and participating in metabolism when provided in sufficient amounts (at least 10^6 viable CFU/g). Integral to our intestinal flora, these microorganisms employ diverse mechanisms of actions.
Mechanisms of actions of probiotics
- Direct antagonism, pH modulation, competition for space, nutrient competition, Production of antimicrobial agents, organic acids, and bacteriocins
- Synthesis of nutrients for epithelial cells and gut bacteria
- Maintenance of mucosal integrity
- Regulation of gut motility
- Enhancement of intestinal barrier function
- Inhibition of bacterial adherence
- Prevention of osteoporosis by increasing bone density
- Hypocholesterolemic action
- Anti-carcinogenic and anti-mutagenic activities
- Stimulation of the intestinal receptor of innate-immunity immunomodulation
- Production of H_{2}*O_{2} promoting epithelial restitution
- Anti-allergenic activities
Recent medical advancements underscore the positive role of communication between gut microbiota and other organs, such as the microbiota-gut-liver axis, microbiota-gut-brain axis, and gut-lung axis.
A healthy microbiota not only prevents infections, autoimmune conditions, and allergies but also serves as an adjuvant therapy, reducing symptoms in clinical states. Probiotics play a pivotal role in preserving the balance of normal intestinal microbiota, improving the immune system, and offering an alternative to antibiotics, thereby mitigating the risk of antimicrobial resistance.
The most common genera identified as probiotics are Lactobacillus and Bifidobacterium. The therapeutic effects of probiotics are strictly dependent on strain and dose. While predominantly found in the human intestine, probiotic microorganisms also exist in other ecological environments, making their actions non-universal to all bacteria or human tissues. Numerous in vitro and animal studies have highlighted promising therapeutic applications, as detailed below.
Probiotics in action: Therapeutic Uses
- Gastrointestinal diseases, including gastroenteritis and inflammatory bowel disease
- Allergy management
- Respiratory diseases, such as asthma, cystic fibrosis, and COVID-19
- Neurological, psychiatric, and liver diseases
- Urinary tract infections
- Metabolic syndrome, including diabetes, obesity, cardiovascular disease, and cholesterol regulation
- Cancer prevention
- Oral diseases like gingivitis, periodontitis, dental caries, halitosis, and oral candidiasis
- Autoimmune diseases: Sjogren’s syndrome, rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis
- Bacterial vaginosis and osteoporosis.
Adverse effects reported in probiotics include abdominal cramps, bloating, flatulence, gas, and loose stools. Their use is not recommended for immunocompromised patients, especially those on corticosteroids, immunosuppressive therapy, post-transplant, and oncology. Patients with prosthetic valves are advised against probiotics due to an increased risk of infective endocarditis.
In recent advances, the term “symbiotic” initially combined probiotics and prebiotics. It is now defined as “a mixture comprising live microorganisms and substrate(s), selectively utilized by the host, that confers a health benefit to the host.