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Pathogenic bacteria are also the cause of high infant mortality rates in developing countries. [5] A GBD study estimated the global death rates from (33) bacterial pathogens, finding such infections contributed to one in 8 deaths (or ~7.7 million deaths), which could make it the second largest cause of death globally in 2019. [6] [3]
This is an accepted version of this page This is the latest accepted revision, reviewed on 10 March 2025. Biological entity that causes disease in its host For other uses, see Pathogen (disambiguation). "Germs" redirects here. For other uses, see Germs (disambiguation). In biology, a pathogen, in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may ...
This is a list of bacteria that are significant in medicine. For viruses, see list of viruses ... List of human diseases associated with infectious pathogens
A human pathogen is a pathogen (microbe or microorganism such as a virus, bacterium, prion, or fungus) that causes disease in humans.. The human physiological defense against common pathogens (such as Pneumocystis) is mainly the responsibility of the immune system with help by some of the body's normal microbiota.
Graphic depicting the human skin microbiota, with relative prevalences of various classes of bacteria. The human microbiome is the aggregate of all microbiota that reside on or within human tissues and biofluids along with the corresponding anatomical sites in which they reside, [1] [2] including the gastrointestinal tract, skin, mammary glands, seminal fluid, uterus, ovarian follicles, lung ...
Bacteria were first observed by Antonie van Leeuwenhoek in 1676, using a single-lens microscope of his own design. [3] He did not distinguish bacteria as a separate type of microorganism, calling all microorganisms, including bacteria, protists, and microscopic animals, "animalcules".
All are microorganisms except some eukaryote groups. Single-celled microorganisms were the first forms of life to develop on Earth, approximately 3.5 billion years ago. [30] [31] [32] Further evolution was slow, [33] and for about 3 billion years in the Precambrian eon, (much of the history of life on Earth), all organisms were microorganisms.
Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea. [5]