Organism
In biology, an organism is any individual entity that exhibits the properties of life. It is a synonym for "life form". Organisms are classified by taxonomy into specified groups such as the multicellular animals and fungi. All types of organisms are capable of reproduction and development, some degree of response to stimuli. Humans are multicellular animals composed of many trillions of cells which differentiate during development into specialized tissues and organs. An organism may be either a eukaryote. Prokaryotes are represented by two separate domains -- archaea. Eukaryotic organisms are characterized by the presence of a membrane-bound cell nucleus and contain additional membrane-bound compartments called organelles. Fungi and plants are examples of kingdoms of organisms within the eukaryotes. Estimates on the number of Earth's current species range from 10 million to 14 million, of which only about 1.2 million have been documented. More than 99% of all species, amounting to over five billion species, that lived are estimated to be extinct.
In 2016, a set of 355 genes from the last universal common ancestor of all organisms was identified. The term "organism" first appeared in the English language in 1703 and took on its current definition by 1834, it is directly related to the term "organization". There is a long tradition of defining organisms as self-organizing beings, going back at least to Immanuel Kant's 1790 Critique of Judgment. An organism may be defined as an assembly of molecules functioning as a more or less stable whole that exhibits the properties of life. Dictionary definitions can be broad, using phrases such as "any living structure, such as a plant, fungus or bacterium, capable of growth and reproduction". Many definitions exclude viruses and possible man-made non-organic life forms, as viruses are dependent on the biochemical machinery of a host cell for reproduction. A superorganism is an organism consisting of many individuals working together as a single functional or social unit. There has been controversy about the best way to define the organism and indeed about whether or not such a definition is necessary.
Several contributions are responses to the suggestion that the category of "organism" may well not be adequate in biology. Viruses are not considered to be organisms because they are incapable of autonomous reproduction, growth or metabolism; this controversy is problematic because some cellular organisms are incapable of independent survival and live as obligatory intracellular parasites. Although viruses have a few enzymes and molecules characteristic of living organisms, they have no metabolism of their own; this rules out autonomous reproduction: they can only be passively replicated by the machinery of the host cell. In this sense, they are similar to inanimate matter. While viruses sustain no independent metabolism and thus are not classified as organisms, they do have their own genes, they do evolve by mechanisms similar to the evolutionary mechanisms of organisms; the most common argument in support of viruses as living organisms is their ability to undergo evolution and replicate through self-assembly.
Some scientists argue. In fact, viruses are evolved by their host cells, meaning that there was co-evolution of viruses and host cells. If host cells did not exist, viral evolution would be impossible; this is not true for cells. If viruses did not exist, the direction of cellular evolution could be different, but cells would be able to evolve; as for the reproduction, viruses rely on hosts' machinery to replicate. The discovery of viral metagenomes with genes coding for energy metabolism and protein synthesis fueled the debate about whether viruses belong in the tree of life; the presence of these genes suggested. However, it was found that the genes coding for energy and protein metabolism have a cellular origin. Most these genes were acquired through horizontal gene transfer from viral hosts. Organisms are complex chemical systems, organized in ways that promote reproduction and some measure of sustainability or survival; the same laws that govern non-living chemistry govern the chemical processes of life.
It is the phenomena of entire organisms that determine their fitness to an environment and therefore the survivability of their DNA-based genes. Organisms owe their origin and many other internal functions to chemical phenomena the chemistry of large organic molecules. Organisms are complex systems of chemical compounds that, through interaction and environment, play a wide variety of roles. Organisms are semi-closed chemical systems. Although they are individual units of life, they are not closed to the environment around them. To operate they take in and release energy. Autotrophs produce usable energy using light from the sun or inorganic compounds while heterotrophs take in organic compounds from the environment; the primary chemical element in these compounds is carbon. The chemical properties of this element such as its grea
Escherichia coli
Escherichia coli known as E. coli, is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus Escherichia, found in the lower intestine of warm-blooded organisms. Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in their hosts, are responsible for product recalls due to food contamination. The harmless strains are part of the normal microbiota of the gut, can benefit their hosts by producing vitamin K2, preventing colonization of the intestine with pathogenic bacteria, having a symbiotic relationship. E. coli is expelled into the environment within fecal matter. The bacterium grows massively in fresh fecal matter under aerobic conditions for 3 days, but its numbers decline afterwards. E. Coli and other facultative anaerobes constitute about 0.1% of gut microbiota, fecal–oral transmission is the major route through which pathogenic strains of the bacterium cause disease. Cells are able to survive outside the body for a limited amount of time, which makes them potential indicator organisms to test environmental samples for fecal contamination.
A growing body of research, has examined environmentally persistent E. coli which can survive for extended periods outside a host. The bacterium can be grown and cultured and inexpensively in a laboratory setting, has been intensively investigated for over 60 years. E. coli is a chemoheterotroph whose chemically defined medium must include a source of carbon and energy. E. coli is the most studied prokaryotic model organism, an important species in the fields of biotechnology and microbiology, where it has served as the host organism for the majority of work with recombinant DNA. Under favorable conditions, it takes up to 20 minutes to reproduce. E. coli is a facultative anaerobic and nonsporulating bacterium. Cells are rod-shaped, are about 2.0 μm long and 0.25–1.0 μm in diameter, with a cell volume of 0.6–0.7 μm3. E. Coli stains Gram-negative because its cell wall is composed of a thin peptidoglycan layer and an outer membrane. During the staining process, E. coli picks up the color of the counterstain safranin and stains pink.
The outer membrane surrounding the cell wall provides a barrier to certain antibiotics such that E. coli is not damaged by penicillin. Strains that possess flagella are motile; the flagella have a peritrichous arrangement. It attaches and effaces to the microvilli of the intestines via an adhesion molecule known as intimin. E. coli can live on a wide variety of substrates and uses mixed-acid fermentation in anaerobic conditions, producing lactate, ethanol and carbon dioxide. Since many pathways in mixed-acid fermentation produce hydrogen gas, these pathways require the levels of hydrogen to be low, as is the case when E. coli lives together with hydrogen-consuming organisms, such as methanogens or sulphate-reducing bacteria. Optimum growth of E. coli occurs at 37 °C, but some laboratory strains can multiply at temperatures up to 49 °C. E. coli grows in a variety of defined laboratory media, such as lysogeny broth, or any medium that contains glucose, ammonium phosphate monobasic, sodium chloride, magnesium sulfate, potassium phosphate dibasic, water.
Growth can be driven by aerobic or anaerobic respiration, using a large variety of redox pairs, including the oxidation of pyruvic acid, formic acid and amino acids, the reduction of substrates such as oxygen, fumarate, dimethyl sulfoxide, trimethylamine N-oxide. E. coli is classified as a facultative anaerobe. It uses oxygen when it is available, it can, continue to grow in the absence of oxygen using fermentation or anaerobic respiration. The ability to continue growing in the absence of oxygen is an advantage to bacteria because their survival is increased in environments where water predominates; the bacterial cell cycle is divided into three stages. The B period occurs between the beginning of DNA replication; the C period encompasses the time it takes to replicate the chromosomal DNA. The D period refers to the stage between the conclusion of DNA replication and the end of cell division; the doubling rate of E. coli is higher. However, the length of the C and D periods do not change when the doubling time becomes less than the sum of the C and D periods.
At the fastest growth rates, replication begins before the previous round of replication has completed, resulting in multiple replication forks along the DNA and overlapping cell cycles. E. coli and related bacteria possess the ability to transfer DNA via bacterial conjugation or transduction, which allows genetic material to spread horizontally through an existing population. The process of transduction, which uses the bacterial virus called a bacteriophage, is where the spread of the gene encoding for the Shiga toxin from the Shigella bacteria to E. coli helped produce E. coli O157:H7, the Shiga toxin-producing strain of E. coli. E. coli encompasses an enormous population of bacteria that exhibit a high degree of both genetic and phenotypic diversity. Genome sequencing of a large number of isolates of E. coli and related bacteria shows that a taxonomic reclassification would be desirable. However, this has not been done due to its medical importance, E. coli remains one of the most diverse bacterial species: only 20% of the genes in a typical E. coli genome is shared among all strains.
In fact, from the evolutionary point of view, the members of genus Shigella (S. dysenteriae, S. fle
Aerosol
An aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. Aerosols can be anthropogenic. Examples of natural aerosols are fog, forest exudates and geyser steam. Examples of anthropogenic aerosols are haze, particulate air pollutants and smoke; the liquid or solid particles have diameters <1 μm. In general conversation, aerosol refers to an aerosol spray that delivers a consumer product from a can or similar container. Other technological applications of aerosols include dispersal of pesticides, medical treatment of respiratory illnesses, convincing technology. Diseases can spread by means of small droplets in the breath called aerosols. Aerosol science covers generation and removal of aerosols, technological application of aerosols, effects of aerosols on the environment and people, other topics. An aerosol is defined as a suspension system of liquid particles in a gas. An aerosol includes both the particles and the suspending gas, air. Frederick G. Donnan first used the term aerosol during World War I to describe an aero-solution, clouds of microscopic particles in air.
This term developed analogously to the term hydrosol, a colloid system with water as the dispersed medium. Primary aerosols contain. Various types of aerosol, classified according to physical form and how they were generated, include dust, mist and fog. There are several measures of aerosol concentration. Environmental science and health uses the mass concentration, defined as the mass of particulate matter per unit volume with units such as μg/m3. Used is the number concentration, the number of particles per unit volume with units such as number/m3 or number/cm3; the size of particles has a major influence on their properties, the aerosol particle radius or diameter is a key property used to characterise aerosols. Aerosols vary in their dispersity. A monodisperse aerosol, producible in the laboratory, contains particles of uniform size. Most aerosols, however, as polydisperse colloidal systems, exhibit a range of particle sizes. Liquid droplets are always nearly spherical, but scientists use an equivalent diameter to characterize the properities of various shapes of solid particles, some irregular.
The equivalent diameter is the diameter of a spherical particle with the same value of some physical property as the irregular particle. The equivalent volume diameter is defined as the diameter of a sphere of the same volume as that of the irregular particle. Used is the aerodynamic diameter. For a monodisperse aerosol, a single number—the particle diameter—suffices to describe the size of the particles. However, more complicated particle-size distributions describe the sizes of the particles in a polydisperse aerosol; this distribution defines the relative amounts of particles, sorted according to size. One approach to defining the particle size distribution uses a list of the sizes of every particle in a sample. However, this approach proves tedious to ascertain in aerosols with millions of particles and awkward to use. Another approach splits the complete size range into intervals and finds the number of particles in each interval. One can visualize these data in a histogram with the area of each bar representing the proportion of particles in that size bin normalised by dividing the number of particles in a bin by the width of the interval so that the area of each bar is proportionate to the number of particles in the size range that it represents.
If the width of the bins tends to zero, one gets the frequency function: d f = f d d p where d p is the diameter of the particles d f is the fraction of particles having diameters between d p and d p + d d p f is the frequency functionTherefore, the area under the frequency curve between two sizes a and b represents the total fraction of the particles in that size range: f a b = ∫ a b f d d p It can be formulated in terms of the total number density N: d N = N d d p Assuming spherical aerosol particles, the aerosol surface area per unit volume is given by the second moment: S = π / 2 ∫ 0 ∞ N d p 2 d d p And the third moment gives the total volume concentration of the particles: V = π / 6 ∫ 0 ∞ N (
Dow Chemical Company
The Dow Chemical Company referred to as Dow, was an American multinational chemical corporation headquartered in Midland, United States, the predecessor of the merged company DowDuPont. In 2017, prior to the merger, it was the second-largest chemical manufacturer in the world by revenue and the third-largest chemical company in the world by market capitalization, it ranked second in the world by chemical production in 2014. Dow manufactures plastics and agricultural products. With a presence in about 160 countries, it employs about 54,000 people worldwide; the company has seven different major operating segments, with a wide variety of products made by each one. Dow's 2012 sales totaled $57 billion. Dow has been called the "chemical companies' chemical company" in that most of its sales are to other industries rather than end-users. Dow sells directly to end-users in the human and animal health and consumer products markets. Dow is a member of the American Chemistry Council; the company tagline is "Solutionism".
On September 1, 2017, it merged with DuPont to create DowDuPont. In March 2018, it was announced that Jeff Fettig would become executive chairman of DowDuPont on July 1, 2018, Jim Fitterling would become CEO of Dow Chemical on April 1, 2018. On April 1, 2019, Dow completed separation from DowDuPont. Dow is a large producer of plastics, including polystyrene, polyethylene and synthetic rubber, it is a major producer of ethylene oxide, various acrylates and cellulose resins. It produces agricultural chemicals including the pesticide Lorsban and consumer products including Styrofoam; some Dow consumer products including Saran wrap, Ziploc bags and Scrubbing Bubbles were sold to S. C. Johnson & Son in 1997. Performance plastics make up 25 percent of Dow's sales, with many products designed for the automotive and construction industries; the plastics include polyolefins such as polyethylene and polypropylene, as well as polystyrene used to produce Styrofoam insulating material. Dow manufactures epoxy resin intermediates including bisphenol epichlorohydrin.
Saran resins and films are based on polyvinylidene chloride The Performance Chemicals segment produces chemicals and materials for water purification, paper coatings and advanced electronics. Major product lines include nitroparaffins, such as nitromethane, used in the pharmaceutical industry and manufactured by Angus Chemical Company, a wholly owned subsidiary of The Dow Chemical Co. Important polymers include Dowex ion exchange resins and polystyrene latex, as well as Carbowax polyethylene glycols. Specialty chemicals are used as starting materials for production of agrochemicals and pharmaceuticals. Dow Water and Process Solutions is a business unit which manufactures Filmtec reverse osmosis membranes which are used to purify water for human use in the Middle East; the technology was used during 2008 Summer Olympics. Agricultural Sciences, or, provides 7 percent of sales and is responsible for a range of insecticides and fungicides. Seeds from genetically modified plants are an important area of growth for the company.
Dow AgroSciences sells seeds commercially under the following brands: Mycogen, PhytoGen and Hyland Seeds in Canada. Basic plastics end up in everything from diaper liners to beverage bottles and oil tanks. Products are based on the three major polyolefins – polystyrene and polypropylene. Basic chemicals are used internally by Dow as raw materials and are sold worldwide. Markets include dry cleaning and coatings, snow and ice control and the food industry. Major products include ethylene glycol, caustic soda and vinyl chloride monomer. Ethylene oxide and propylene oxide and the derived alcohols ethylene glycol and propylene glycol are major feedstocks for the manufacture of plastics such as polyurethane and PET; the Hydrocarbons and Energy operating segment oversees energy management at Dow. Fuels and oil-based raw materials are procured. Major feedstocks for Dow are provided by this group, including ethylene, propylene, 1,3-butadiene and styrene. Dow was founded in 1897 by chemist Herbert Henry Dow, who invented a new method of extracting the bromine, trapped underground in brine at Midland, Michigan.
Dow sold only bleach and potassium bromide, achieving a bleach output of 72 tons a day in 1902. Early in the company's history, a group of British manufacturers tried to drive Dow out of the bleach business by cutting prices. Dow survived by cutting its prices and, although losing about $90,000 in income, began to diversify its product line. In 1905, German bromide producers began dumping bromides at low cost in the U. S. in an effort to prevent Dow from expanding its sales of bromides in Europe. Instead of competing directly for market share with the German producers, Dow bought the cheap German-made bromides and shipped them back to Europe; this undercut his German competitors. In its early history, Dow set a tradition of diversifying its product line. Within twenty years, Dow had become a major producer of agricultural chemicals, elemental chlorine and other dyestuffs, magnesium metal. During World War I, Dow Chemical supplied many war materials the United States had imported from Germany. Dow produced magnesium for incendiary flares, monochlorobenzene and
Sharps waste
Sharps waste is a form of biomedical waste composed of used "sharps", which includes any device or object used to puncture or lacerate the skin. Sharps waste is classified as biohazardous waste and must be handled. Common medical materials treated as sharps waste are: Hypodermic needles Disposable scalpels and blades Contaminated glass and some plastics In addition to needles and blades, anything attached to them will be considered sharps waste, such syringes and injection devices. Blades can include razors, scalpels, X-Acto knife, scissors, or any other medical items used for cutting in the medical setting, regardless of if they have been contaminated with biohazardous material. While glass and sharp plastic are considered sharps waste, their handling methods can vary. Glass items which have been contaminated with a biohazardous material will be treated with the same concern as needles and blades if unbroken. If glass is contaminated, it is still treated as a sharp, because it can break during the disposal process.
Contaminated plastic items which are not sharp can be disposed of in a biohazardous waste receptacle instead of a sharps container. As a biohazardous material, injuries from sharps waste can pose a large public health concern. By penetrating the skin, it is possible for this waste to spread blood-borne pathogens; the spread of these pathogens is directly responsible for the transmission of blood-borne diseases, such as hepatitis B, hepatitis C, HIV. Health care professionals expose themselves to the risk of transmission of these diseases when handling sharps waste; the large volume handled by health care professionals on a daily basis increases the chance that an injury may occur. The general public can be at risk to injuries from sharps waste as well when improperly disposed of by injection drug users. A sharps container is a hard plastic container, used to safely dispose of hypodermic needles and other sharp medical instruments, such as an IV catheters and disposable scalpels. Sharps containers may be single use which are disposed of with the waste inside, or reusable which are robotically emptied and sterilized before being returned for re-use.
Needles are dropped into the container through an opening in the top. Needles should never be pushed or forced into the container, as damage to the container and/or needlestick injuries may result. Sharps containers should not be filled above the indicated line two-thirds full. In North America, sharps containers are red, elsewhere are yellow. Airports and large institutions have sharps containers available in restrooms for safe disposal for users of injection drugs, such as insulin-dependent diabetics. People injecting drugs in their homes may substitute other hard-sided containers such as empty milk jugs for disposal of needles. Extreme care must be taken in the disposal of sharps waste; the goal in sharps waste management is to safely handle all materials until they can be properly disposed. The final step in the disposal of sharps waste is to dispose of them in an autoclave. A less common approach is to incinerate them. Steps must be taken along the way to minimize the risk of injury from this material, while maximizing the amount of sharps material disposed.
Health care workers are to minimize their interaction with sharps waste by disposing of it in a sealable container. Attempts by health care workers to disassemble sharps waste is kept to a minimum. Strict hospital protocols and government regulations ensure that hospital workers handle sharps waste safely and dispose of it effectively. Self-locking and sealable sharps containers are made of plastic so that the sharps can not penetrate through the sides; such units are designed so that the whole container can be disposed of with other biohazardous waste. Single use sharps containers of various sizes are sold throughout the world. Large medical facilities may have their own'mini' autoclave in which these sharps containers are disposed of with other medical wastes; this minimizes the distance the containers have to travel and the number of people to come in contact with the sharps waste. Smaller clinics or offices without such facilities are required by federal regulations to hire the services of a company that specializes in transporting and properly disposing of the hazardous wastes.
NIOSH found through results from focus groups that accommodation, functionality and visibility are four areas of high importance to be able to ensure safe discarding of sharps. The studies found it was important to have containers that are easy to use with little need for training to be able to use; the containers should be visible in any areas that sharps are used and be placed in such degree that spillage and injury will not be to occur with use. Recent legislation in France has stated that pharmaceutical companies supplying self injection medications are responsible for the disposal of spent needles. Popular needle clippers and caps are no longer acceptable as safety devices and either sharps box or needle destruction devices are required. Disposal methods vary by country and locale, but common methods of disposal are either by truck service or, in the United States, by disposal of sharps through the mail. Truck service involves trained personnel collecting sharps waste, medical waste, at the point of generation and hauling it away by truck to a destruction facility.
The mail-back sharps disposal method allows generators to ship sharps waste to the disposal facility directly through the U. S. mail in specially approved shipping containers. Mail-back sharps disposal allows waste generators to dispose of smaller amounts of sharps more economically than
Biosafety level
A biosafety level is a set of biocontainment precautions required to isolate dangerous biological agents in an enclosed laboratory facility. The levels of containment range from the lowest biosafety level 1 to the highest at level 4. In the United States, the Centers for Disease Control and Prevention have specified these levels. In the European Union, the same biosafety levels are defined in a directive. In Canada the four levels are known as Containment Levels. Facilities with these designations are sometimes given as P1 through P4, as in the term "P3 laboratory". At the lowest level of biosafety, precautions may consist of regular hand-washing and minimal protective equipment. At higher biosafety levels, precautions may include airflow systems, multiple containment rooms, sealed containers, positive pressure personnel suits, established protocols for all procedures, extensive personnel training, high levels of security to control access to the facility; the first prototype Class III biosafety cabinet was fashioned in 1943 by Hubert Kaempf Jr. a U.
S. Army soldier, under the direction of Dr. Arnold G. Wedum, Director of Industrial Health and Safety at the United States Army Biological Warfare Laboratories, Camp Detrick, Maryland. Kaempf was tired of his MP duties at Detrick and was able to transfer to the sheet metal department working with the contractor, the H. K. Ferguson Co. On 18 April 1955, fourteen representatives met at Camp Detrick in Maryland; the meeting was to share knowledge and experiences regarding biosafety, chemical and industrial safety issues that were common to the operations at the three principal biological warfare laboratories of the U. S. Army; because of the potential implication of the work conducted at biological warfare laboratories, the conferences were restricted to top level security clearances. Beginning in 1957, these conferences were planned to include non-classified sessions as well as classified sessions to enable broader sharing of biological safety information, it was not until 1964, that conferences were held in a government installation not associated with a biological warfare program.
Over the next ten years, the biological safety conferences grew to include representatives from all federal agencies that sponsored or conducted research with pathogenic microorganisms. By 1966 it began to include representatives from universities, private laboratories and industrial complexes. Throughout the 1970s, participation in the conferences continued to expand and by 1983 discussions began regarding the creation of a formal organization; the American Biological Safety Association was established in 1984 and a constitution and bylaws were drafted the same year. As of 2008, ABSA includes some 1,600 members in its professional association. Biosafety level 1 is suitable for work with well-characterized agents which do not cause disease in healthy humans. In general, these agents should pose minimal potential hazard to laboratory personnel and the environment. At this level, precautions are limited relative to other levels. Laboratory personnel must wash their hands upon exiting the lab. Research with these agents may be performed on standard open laboratory benches without the use of special containment equipment.
However and drinking are prohibited in laboratory areas. Infectious material must be decontaminated before disposal, either by adding an appropriate disinfectant, or by packaging for decontamination elsewhere. Personal protective equipment is only required for circumstances where personnel might be exposed to hazardous material. BSL-1 laboratories must have a door which can be locked to limit access to the lab, however it is not necessary for BSL-1 labs to be isolated from the general building; this level of biosafety is appropriate for work with several kinds of microorganisms including non-pathogenic Escherichia coli, Bacillus subtilis, Saccharomyces cerevisiae and other organisms not suspected to contribute to human disease. Due to the relative ease and safety of maintaining a BSL-1 laboratory, these are the types of laboratories used as teaching spaces for high schools and colleges. At this level, all precautions used at Biosafety Level 1 are followed, some additional precautions are taken.
BSL-2 differs from BSL-1 in that: Laboratory personnel have specific training in handling pathogenic agents and are directed by scientists with advanced training. Access to the laboratory is limited. Extreme precautions are taken with contaminated sharp items. Certain procedures in which infectious aerosols or splashes may be created are conducted in biological safety cabinets or other physical containment equipment. Biosafety level 2 is suitable for work involving agents of moderate potential hazard to personnel and the environment; this includes various microbes that cause mild disease to humans, or are difficult to contract via aerosol in a lab setting. Examples include Hepatitis A, B, C viruses, human immunodeficiency virus, pathogenic Escherichia coli, Staphylococcus aureus, Plasmodium falciparum, Toxoplasma gondii. Biosafety level 3 is appropriate for work involving microbes which can cause serious and lethal disease via the inhalation route; this type of work can be done in clinical, teaching, research, or production facilities.
Here, the precautions undertaken in BSL-1 and BSL-2 labs are followed, as well as additional measures including: All laboratory personnel are provided medical surveillance and offered relevant immunizations to reduce the risk of an accidental or unnoticed infection. All procedures involving infectious mater
Salmonella
Salmonella is a genus of rod-shaped Gram-negative bacteria of the family Enterobacteriaceae. The two species of Salmonella are Salmonella Salmonella bongori. S. enterica is the type species and is further divided into six subspecies that include over 2,600 serotypes. Salmonella species are non-spore-forming, predominantly motile enterobacteria with cell diameters between about 0.7 and 1.5 µm, lengths from 2 to 5 µm, peritrichous flagella. They are chemotrophs, obtaining their energy from oxidation and reduction reactions using organic sources, they are facultative aerobes, capable of generating ATP with oxygen when it is available, or when oxygen is not available, using other electron acceptors or fermentation. S. enterica subspecies are found worldwide in the environment. S. bongori is restricted to cold-blooded animals reptiles. Salmonella species are intracellular pathogens. Nontyphoidal serotypes can be transferred from human-to-human, they invade only the gastrointestinal tract and cause salmonellosis, the symptoms of which can be resolved without antibiotics.
However, in sub-Saharan Africa, nontyphoidal Salmonella can be invasive and cause paratyphoid fever, which requires immediate treatment with antibiotics. Typhoidal serotypes can only be transferred from human-to-human, can cause food-borne infection, typhoid fever, paratyphoid fever. Typhoid fever is caused by Salmonella invading the bloodstream, or in addition spreads throughout the body, invades organs, secretes endotoxins; this can lead to life-threatening hypovolemic shock and septic shock, requires intensive care including antibiotics. The collapse of the Aztec society in Mesoamerica is linked to a catastrophic Salmonella outbreak, one of humanity's deadliest, that occurred after the Spanish conquest; the genus Salmonella is part of the family of Enterobacteriaceae. Its taxonomy has the potential to confuse; the genus comprises two species, S. bongori and S. enterica, the latter of, divided into six subspecies: S. e. enterica, S. e. salamae, S. e. arizonae, S. e. diarizonae, S. e. houtenae, S. e. indica.
The taxonomic group contains more than 2500 serotypes defined on the basis of the somatic O and flagellar H antigens. The full name of a serotype is given for example, Salmonella enterica subsp.. Enterica can be abbreviated to Salmonella Typhimurium. Further differentiation of strains to assist clinical and epidemiological investigation may be achieved by antibiotic sensitivity testing and by other molecular biology techniques such as pulsed-field gel electrophoresis, multilocus sequence typing, whole genome sequencing. Salmonellae have been clinically categorized as invasive or noninvasive based on host preference and disease manifestations in humans. Salmonella was first visualized in 1880 by Karl Eberth in the Peyer's patches and spleens of typhoid patients. Four years Georg Theodor Gaffky was able to grow the pathogen in pure culture. A year after that, medical research scientist Theobald Smith discovered what would be known as Salmonella enterica. At the time, Smith was working as a research laboratory assistant in the Veterinary Division of the United States Department of Agriculture.
The department was under the administration of a veterinary pathologist. Salmonella Choleraesuis was thought to be the causative agent of hog cholera, so Salmon and Smith named it "Hog-cholerabacillus"; the name Salmonella was not used until 1900, when Joseph Leon Lignières proposed that the pathogen discovered by Salmon's group be called Salmonella in his honor. Most subspecies of Salmonella produce hydrogen sulfide, which can be detected by growing them on media containing ferrous sulfate, such as is used in the triple sugar iron test. Most isolates exist in two phases, a motile phase I and a nonmotile phase II. Cultures that are nonmotile upon primary culture may be switched to the motile phase using a Craigie tube or ditch plate. RVS broth can be used to enrich for Salmonella species for detection in a clinical sample. Salmonella can be detected and subtyped using multiplex or real-time polymerase chain reactions from extracted Salmonella DNA. Mathematical models of Salmonella growth kinetics have been developed for chicken, pork and melons.
Salmonella reproduce asexually with a cell division interval of 40 minutes. Salmonella species lead predominantly host-associated lifestyles, but the bacteria were found to be able to persist in a bathroom setting for weeks following contamination, are isolated from water sources, which act as bacterial reservoirs and may help to facilitate transmission between hosts. Salmonella is notorious for its ability to survive desiccation and can persist for years in dry environments and foods; the bacteria are not destroyed by freezing. They perish after being heated to 60 °C for 12 min. To protect against Salmonella infection, heating food for at least 10 minutes to an internal temperature of 75 °C is recommended. Salmonella species can be found in the digestive tracts of humans and animals reptiles. Salmonella on the skin of reptiles or amphibians can be passed to people. Food and water can be contaminated with the bacteria if they come in contact with the feces of infected people
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