Why do only some bacteria cause disease?

Because most bacteria can not grow inside our body as it doesn't provide them appropriate growth conditions. Others which may find human body favorable for their growth can not enter the body. read more

Bacteria and Archae have been around for much longer than any other life forms and occupy more ecological niches than plants and animals. So form the viewpoint of bacterial ecology causing disease in humans is a marginal activity. Since we evolved in their world some have developed the ability to cause disease. read more

They have a different structure (morphology) to bacteria and are not susceptible to antibiotics. In spite of these important structural and cultural differences, both bacteria and viruses can cause disease in similar ways: they invade and multiply within the host by evading the immune system. read more

In healthy individuals, however, pathogens cause no disease; they simply coexist with their host and the rest of the human microbiome, the collection of all microorganisms living in the human body. Researchers must now figure out why some pathogens turn deadly and under what conditions, likely revising current concepts of how microorganisms cause disease. read more