Question: When bacteria is formed by a parasitic association with other organisms, what are they classified as?
About the article "Bacteria", section "Pathogens".

Candidate passages:
If bacteria form a parasitic association with other organisms, they are classed as pathogens.
Pathogenic bacteria are a major cause of human death and disease and cause infections such as tetanus, typhoid fever, diphtheria, syphilis, cholera, foodborne illness, leprosy and tuberculosis.
A pathogenic cause for a known medical disease may only be discovered many years after, as was the case with "Helicobacter pylori" and peptic ulcer disease.
Bacterial diseases are also important in agriculture, with bacteria causing leaf spot, fire blight and wilts in plants, as well as Johne's disease, mastitis, salmonella and anthrax in farm animals.
Each species of pathogen has a characteristic spectrum of interactions with its human hosts.
Some organisms, such as "Staphylococcus" or "Streptococcus", can cause skin infections, pneumonia, meningitis and even overwhelming sepsis, a systemic inflammatory response producing shock, massive vasodilation and death.
Yet these organisms are also part of the normal human flora and usually exist on the skin or in the nose without causing any disease at all.
Other organisms invariably cause disease in humans, such as the Rickettsia, which are obligate intracellular parasites able to grow and reproduce only within the cells of other organisms.
One species of Rickettsia causes typhus, while another causes Rocky Mountain spotted fever.
"Chlamydia", another phylum of obligate intracellular parasites, contains species that can cause pneumonia, or urinary tract infection and may be involved in coronary heart disease.
Finally, some species such as "Pseudomonas aeruginosa", "Burkholderia cenocepacia", and "Mycobacterium avium" are opportunistic pathogens and cause disease mainly in people suffering from immunosuppression or cystic fibrosis.
Bacterial infections may be treated with antibiotics, which are classified as bacteriocidal if they kill bacteria, or bacteriostatic if they just prevent bacterial growth.
There are many types of antibiotics and each class inhibits a process that is different in the pathogen from that found in the host.
An example of how antibiotics produce selective toxicity are chloramphenicol and puromycin, which inhibit the bacterial ribosome, but not the structurally different eukaryotic ribosome.
Antibiotics are used both in treating human disease and in intensive farming to promote animal growth, where they may be contributing to the rapid development of antibiotic resistance in bacterial populations.
Infections can be prevented by antiseptic measures such as sterilizing the skin prior to piercing it with the needle of a syringe, and by proper care of indwelling catheters.
Surgical and dental instruments are also sterilized to prevent contamination by bacteria.
Disinfectants such as bleach are used to kill bacteria or other pathogens on surfaces to prevent contamination and further reduce the risk of infection.
Bacteria possess a compact genome architecture distinct from eukaryotes in two important ways: bacteria show a strong correlation between genome size and number of functional genes in a genome, and those genes are structured into operons.
The main reason for the relative density of bacterial genomes compared to eukaryotic genomes (especially multicellular eukaryotes) is the presence of noncoding DNA in the form of intergenic regions and introns.
Some notable exceptions include recently formed pathogenic bacteria.
This was initially described in a study by Cole "et al".
in which "Mycobacterium leprae" was discovered to have a significantly higher percentage of pseudogenes to functional genes (~40%) than its free-living ancestors.
Furthermore, amongst species of bacteria, there is relatively little variation in genome size when compared with the genome sizes of other major groups of life.
Genome size is of little relevance when considering the number of functional genes in eukaryotic species.
In bacteria however, the strong correlation between the number of genes and the genome size makes the size of bacterial genomes an interesting topic for research and discussion.
The general trends of bacterial evolution indicate that bacteria started as free-living organisms.
Evolutionary paths led some bacteria to become pathogens and symbionts.
The lifestyles of bacteria play an integral role in their respective genome sizes.
Free-living bacteria have the largest genomes out of the three types of bacteria; however, they have fewer pseudogenes than bacteria that have recently acquired pathogenicity.
Facultative and recently evolved pathogenic bacteria exhibit a smaller genome size than free-living bacteria, yet they have more pseudogenes than any other form of bacteria.
Obligate bacterial symbionts or pathogens have the smallest genomes and the fewest pseudogenes of the three groups.
The relationship between life-styles of bacteria and genome size raises questions as to the mechanisms of bacterial genome evolution.
Researchers have developed several theories to explain the patterns of genome size evolution amongst bacteria. 
It closely resembles certain ciliates and was originally classified with them, but is now considered a flagellate.
The cell is somewhat flattened, with multiple smooth flagella arranged in rows running from the front to the back, and has an anterior mouth supported by rods.
They feed on bacteria, diatoms, and other smaller organisms.
There are 2-16 nuclei, but they are not differentiated into macronuclei and micronuclei as occurs in ciliates. 
Bacteria (; "singular": bacterium) constitute a large domain of prokaryotic microorganisms.
Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals.
Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats.
Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep portions of Earth's crust.
Bacteria also live in symbiotic and parasitic relationships with plants and animals.
They are also known to have flourished in manned spacecraft.
There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water.
There are approximately 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants and animals.
Bacteria are vital in recycling nutrients, with many of the stages in nutrient cycles dependent on these organisms, such as the fixation of nitrogen from the atmosphere and putrefaction.
In the biological communities surrounding hydrothermal vents and cold seeps, bacteria provide the nutrients needed to sustain life by converting dissolved compounds such as hydrogen sulphide and methane to energy.
On 17 March 2013, researchers reported data that suggested bacterial life forms thrive in the Mariana Trench, the deepest spot on the Earth.
Other researchers reported related studies that microbes thrive inside rocks up to 1900 feet below the sea floor under 8500 feet of ocean off the coast of the northwestern United States.
According to one of the researchers,"You can find microbes everywhere — they're extremely adaptable to conditions, and survive wherever they are.
"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 as there are human cells in the body, with the largest number of the human flora being in the gut flora, and a large number on the skin.
The vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, and some are beneficial.
However, several 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 are also used in farming, making antibiotic resistance a growing problem.
In industry, bacteria are important in sewage treatment and the breakdown of oil spills, the production of cheese and yogurt through fermentation, and the recovery of gold, palladium, copper and other metals in the mining sector, 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 from an ancient common ancestor.
These evolutionary domains are called "Bacteria" and "Archaea". 
Bacteria exhibit an extremely wide variety of metabolic types.
The distribution of metabolic traits within a group of bacteria has traditionally been used to define their taxonomy, but these traits often do not correspond with modern genetic classifications.
Bacterial metabolism is classified into nutritional groups on the basis of three major criteria: the kind of energy used for growth, the source of carbon, and the electron donors used for growth.
An additional criterion of respiratory microorganisms are the electron acceptors used for aerobic or anaerobic respiration.
Carbon metabolism in bacteria is either heterotrophic, where organic carbon compounds are used as carbon sources, or autotrophic, meaning that cellular carbon is obtained by fixing carbon dioxide.
Heterotrophic bacteria include parasitic types.
Typical autotrophic bacteria are phototrophic cyanobacteria, green sulfur-bacteria and some purple bacteria, but also many chemolithotrophic species, such as nitrifying or sulfur-oxidising bacteria.
Energy metabolism of bacteria is either based on phototrophy, the use of light through photosynthesis, or based on chemotrophy, the use of chemical substances for energy, which are mostly oxidised at the expense of oxygen or alternative electron acceptors (aerobic/anaerobic respiration).
Bacteria are further divided into lithotrophs that use inorganic electron donors and organotrophs that use organic compounds as electron donors.
Chemotrophic organisms use the respective electron donors for energy conservation (by aerobic/anaerobic respiration or fermentation) and biosynthetic reactions (e.g., carbon dioxide fixation), whereas phototrophic organisms use them only for biosynthetic purposes.
Respiratory organisms use chemical compounds as a source of energy by taking electrons from the reduced substrate and transferring them to a terminal electron acceptor in a redox reaction.
This reaction releases energy that can be used to synthesise ATP and drive metabolism.
In aerobic organisms, oxygen is used as the electron acceptor.
In anaerobic organisms other inorganic compounds, such as nitrate, sulfate or carbon dioxide are used as electron acceptors.
This leads to the ecologically important processes of denitrification, sulfate reduction, and acetogenesis, respectively.
Another way of life of chemotrophs in the absence of possible electron acceptors is fermentation, wherein the electrons taken from the reduced substrates are transferred to oxidised intermediates to generate reduced fermentation products (e.g., lactate, ethanol, hydrogen, butyric acid).
Fermentation is possible, because the energy content of the substrates is higher than that of the products, which allows the organisms to synthesise ATP and drive their metabolism.
These processes are also important in biological responses to pollution; for example, sulfate-reducing bacteria are largely responsible for the production of the highly toxic forms of mercury (methyl- and dimethylmercury) in the environment.
Non-respiratory anaerobes use fermentation to generate energy and reducing power, secreting metabolic by-products (such as ethanol in brewing) as waste.
Facultative anaerobes can switch between fermentation and different terminal electron acceptors depending on the environmental conditions in which they find themselves.
Lithotrophic bacteria can use inorganic compounds as a source of energy.
Common inorganic electron donors are hydrogen, carbon monoxide, ammonia (leading to nitrification), ferrous iron and other reduced metal ions, and several reduced sulfur compounds.
In unusual circumstances, the gas methane can be used by methanotrophic bacteria as both a source of electrons and a substrate for carbon anabolism.
In both aerobic phototrophy and chemolithotrophy, oxygen is used as a terminal electron acceptor, whereas under anaerobic conditions inorganic compounds are used instead.
Most lithotrophic organisms are autotrophic, whereas organotrophic organisms are heterotrophic.
In addition to fixing carbon dioxide in photosynthesis, some bacteria also fix nitrogen gas (nitrogen fixation) using the enzyme nitrogenase.
This environmentally important trait can be found in bacteria of nearly all the metabolic types listed above, but is not universal.
Regardless of the type of metabolic process they employ, the majority of bacteria are able to take in raw materials only in the form of relatively small molecules, which enter the cell by diffusion or through molecular channels in cell membranes.
The Planctomycetes are the exception (as they are in possessing membranes around their nuclear material).
It has recently been shown that "Gemmata obscuriglobus" is able to take in large molecules via a process that in some ways resembles endocytosis, the process used by eukaryotic cells to engulf external items.