Diseases, Conditions, Syndromes

Highly virulent listeriosis pathogen discovered

The bacterium Listeria monocytogenes can cause listeriosis, a life-threatening infection in animals and humans. Contaminated food is a frequent source of infection. Elderly people, people with a weakened immune system and ...

Medical research

Resistance can spread even without the use of antibiotics

Antibiotic resistance does not spread only where and when antibiotics are used in large quantities, ETH researchers conclude from laboratory experiments. Reducing antibiotic use alone is therefore not sufficient to curtail ...

Diseases, Conditions, Syndromes

Study maps genetics of early progression in tuberculosis

While the vast majority of the 1.8 billion people infected with the TB bacterium never experience active disease, an estimated 5 to 15 percent do develop full-blown infections—roughly half of them within 18 months of exposure.

Diseases, Conditions, Syndromes

Can eating poop save you from this deadly bacteria?

Every year, around half a million people in the United States get sick from the bacterium C. diff, often after taking antibiotics. Sounds counterintuitive? This week on Reactions, we break down why that happens, and how an ...

Immunology

Vaccine investigators use bacterium's own protein against it

A team of Agricultural Research Service (ARS) and university scientists is investigating a new "ingredient" for use in vaccinating cattle against Johne's disease, a chronic wasting affliction that costs the U.S. dairy industry ...

Health

How common gut bacteria trigger a lethal autoimmune disease

What causes the immune system, designed to protect us, to turn on the body and attack healthy cells? Common bacteria that reside in the human gut may be partly to blame, say Yale researchers, who studied the origins of a ...

Medical research

Healthy, stress-busting fat found hidden in dirt

Thirty years after scientists coined the term "hygiene hypothesis" to suggest that increased exposure to microorganisms could benefit health, CU Boulder researchers have identified an anti-inflammatory fat in a soil-dwelling ...

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Bacteria

Actinobacteria (high-G+C) Firmicutes (low-G+C) Tenericutes (no wall)

Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Deinococcus-Thermus Fusobacteria Gemmatimonadetes Nitrospirae Proteobacteria Spirochaetes Synergistetes

Acidobacteria Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Dictyoglomi Fibrobacteres Planctomycetes Thermodesulfobacteria Thermotogae

The bacteria [bækˈtɪərɪə] (help·info) (singular: bacterium)[α] are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste, water, and deep in the Earth's crust, as well as in organic matter and the live bodies of plants and animals. There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water; in all, there are approximately five nonillion (5×1030) bacteria on Earth, forming much of the world's biomass. Bacteria are vital in recycling nutrients, with many steps in nutrient cycles depending on these organisms, such as the fixation of nitrogen from the atmosphere and putrefaction. However, most bacteria have not been characterized, and only about half of the phyla of bacteria have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.

There are approximately ten times as many bacterial cells in the human flora of bacteria as there are human cells in the body, with large numbers of bacteria on the skin and as gut flora. The vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, and a few are beneficial. However, a few species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy and bubonic plague. The most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing about 2 million people a year, mostly in sub-Saharan Africa. In developed countries, antibiotics are used to treat bacterial infections and in agriculture, so antibiotic resistance is becoming common. In industry, bacteria are important in sewage treatment, the production of cheese and yoghurt through fermentation, as well as in biotechnology, and the manufacture of antibiotics and other chemicals.

Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. 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 independently from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea.

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