Commensal bacteria stimulate the immune system of the host to enhance defense mechanisms that block pathogen entrance and colonization. Moreover, by creating antimicrobial properties and signals & fighting with other bacteria for food and attachment sites, such bacteria might effectively limit the spread of respiratory infections. In healthy animals, the majority of commensal bacteria live inside the intestine's lumen, although some are also found in immediate contact with the intestinal epithelium. New studies have shown that commensal bacteria may live in stable stomach lymphoid tissues. But every once in a while, especially when they travel to other areas and leave their natural habitat, these commensal bacteria might cause illness. In both old and very and also in young persons, it can spread throughout the rest of the body, causing pneumonia, infection, and meningitis.
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Charles Darwin proposed one of the theory of evolution which can still be observed till date in organism.
Organism have numerous offsprings and only the offspring with characteristics to overcome unfavorable conditions survive and passes such genes to their offsprings
