HOME

TheInfoList



OR:

''Salmonella'' is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
rod-shaped A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name '' Baci ...
(bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of ''Salmonella'' are '' Salmonella enterica'' and '' Salmonella bongori''. ''S. enterica'' is the
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...
and is further divided into six
subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics ( morphology), but that can successfully interbreed. Not all specie ...
that include over 2,600 serotypes. ''Salmonella'' was named after Daniel Elmer Salmon (1850–1914), an American veterinary surgeon. ''Salmonella'' species are non-
spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...
-forming, predominantly motile
enterobacteria Enterobacteriaceae is a large family of Gram-negative bacteria. It was first proposed by Rahn in 1936, and now includes over 30 genera and more than 100 species. Its classification above the level of family is still a subject of debate, but on ...
with cell diameters between about 0.7 and 1.5
μm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of length in the International System of Uni ...
, lengths from 2 to 5 μm, and peritrichous flagella (all around the cell body, allowing them to move). They are chemotrophs, obtaining their energy from oxidation and reduction reactions, using organic sources. They are also facultative anaerobes, capable of generating ATP with oxygen ("aerobically") when it is available, or using other
electron acceptor An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process. Electron acceptors are sometimes mista ...
s or
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
("anaerobically") when
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
is not available. ''Salmonella'' species are intracellular pathogens, of which certain serotypes cause illness. Most infections are due to ingestion of food contaminated by animal feces, or by human feces, such as by a food-service worker at a commercial eatery. ''Salmonella'' serotypes can be divided into two main groups—typhoidal and nontyphoidal. Nontyphoidal serotypes are zoonotic and can be transferred from animal-to-human and from human-to-human. They usually invade only the gastrointestinal tract and cause salmonellosis, the symptoms of which can be resolved without
antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and preventio ...
. However, in
sub-Saharan Africa Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...
, nontyphoidal ''Salmonella'' can be invasive and cause
paratyphoid fever Paratyphoid fever, also known simply as paratyphoid, is a bacterial infection caused by one of the three types of '' Salmonella enterica''. Symptoms usually begin 6–30 days after exposure and are the same as those of typhoid fever. Often, a g ...
, which requires immediate treatment with antibiotics. Typhoidal serotypes can only be transferred from human-to-human, and can cause food-borne infection,
typhoid fever Typhoid fever, also known as typhoid, is a disease caused by '' Salmonella'' serotype Typhi bacteria. Symptoms vary from mild to severe, and usually begin six to 30 days after exposure. Often there is a gradual onset of a high fever over severa ...
, and paratyphoid fever. Typhoid fever is caused by ''Salmonella'' invading the bloodstream (the typhoidal form), or in addition spreading throughout the body, invading organs, and secreting endotoxins (the septic form). This can lead to life-threatening
hypovolemic shock Hypovolemic shock is a form of shock caused by severe hypovolemia (insufficient blood volume or extracellular fluid in the body). It could be the result of severe dehydration through a variety of mechanisms or blood loss. Hypovolemic shock is a ...
and septic shock, and requires intensive care including antibiotics.


Taxonomy

The genus ''Salmonella'' is part of the family of Enterobacteriaceae. Its taxonomy has been revised and has the potential to confuse. The genus comprises two species, ''S. bongori'' and ''S. enterica'', the latter of which is divided into six subspecies: ''S. e. enterica'', ''S. e. salamae'', ''S. e. arizonae'', ''S. e. diarizonae'', ''S. e. houtenae'', and ''S. e. indica''. The taxonomic group contains more than 2500 serotypes (also serovars) defined on the basis of the somatic O (
lipopolysaccharide Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O- antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the out ...
) and flagellar H antigens (the Kauffman–White classification). The full name of a serotype is given as, for example, ''Salmonella enterica'' subsp. ''enterica'' serotype Typhimurium, but can be abbreviated to ''Salmonella'' Typhimurium. Further differentiation of strains to assist clinical and
epidemiological Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evid ...
investigation may be achieved by
antibiotic sensitivity testing Antibiotic sensitivity testing or antibiotic susceptibility testing is the measurement of the susceptibility of bacteria to antibiotics. It is used because bacteria may have resistance to some antibiotics. Sensitivity testing results can allow ...
and by other
molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and phys ...
techniques such as
pulsed-field gel electrophoresis Pulsed field gel electrophoresis is a technique used for the separation of large DNA molecules by applying to a gel matrix an electric field that periodically changes direction. Historical background Standard gel electrophoresis techniques for s ...
, multilocus sequence typing, and, increasingly,
whole genome sequencing Whole genome sequencing (WGS), also known as full genome sequencing, complete genome sequencing, or entire genome sequencing, is the process of determining the entirety, or nearly the entirety, of the DNA sequence of an organism's genome at a ...
. Historically, salmonellae have been clinically categorized as invasive (typhoidal) or noninvasive (nontyphoidal salmonellae) based on host preference and disease manifestations in humans.


History

''Salmonella'' was first visualized in 1880 by Karl Eberth in the Peyer's patches and
spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .
s of typhoid patients. Four years later, Georg Theodor Gaffky was able to successfully grow the pathogen in pure culture. A year after that, medical research scientist Theobald Smith discovered what would be later known as '' Salmonella enterica'' (var. Choleraesuis). At the time, Smith was working as a research laboratory assistant in the Veterinary Division of the
United States Department of Agriculture The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of comme ...
. The division was under the administration of Daniel Elmer Salmon, a veterinary pathologist. Initially, ''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. In the late 1930s, Australian
bacteriologist A bacteriologist is a microbiologist, or similarly trained professional, in bacteriology -- a subdivision of microbiology that studies bacteria, typically pathogenic ones. Bacteriologists are interested in studying and learning about bacteria, ...
Nancy Atkinson established a salmonella typing laboratory – one of only three in the world at the time – at the
Government of South Australia The Government of South Australia, also referred to as the South Australian Government, SA Government or more formally, His Majesty’s Government, is the Australian state democratic administrative authority of South Australia. It is modelled o ...
's Laboratory of Pathology and Bacteriology in
Adelaide Adelaide ( ) is the capital city of South Australia, the state's largest city and the fifth-most populous city in Australia. "Adelaide" may refer to either Greater Adelaide (including the Adelaide Hills) or the Adelaide city centre. The dem ...
(later the Institute of Medical and Veterinary Science). It was here that Atkinson described multiple new strains of salmonella, including Salmonella Adelaide, which was isolated in 1943. Atkinson published her work on salmonellas in 1957.


Serotyping

Serotyping is done by mixing cells with antibodies for a particular antigen. It can give some idea about risk. A 2014 study showed that ''S. reading'' is very common among young
turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolian Peninsula in Western Asia, with a small portion on the Balkan Peninsula ...
samples, but it is not a significant contributor to human salmonellosis. Serotyping can assist in identifying the source of contamination by matching serotypes in people with serotypes in the suspected source of infection. Appropriate prophylactic treatment can be identified from the known antibiotic resistance of the serotype. Looking at the comparison of xMAP ''Salmonella'' Serotyping Assay With Traditional Serotyping and Discordance Resolution by Whole Genome Sequencing, study showed that molecular serotyping is promising as a rapid method for ''Salmonella'' serotyping. Real-Time PCR Assay for Differentiation of Typhoidal and Nontyphoidal ''Salmonella is also available.''


Detection, culture, and growth conditions

Most subspecies of ''Salmonella'' produce
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...
, which can readily 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 and a non-motile phase. 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 also be detected and subtyped using
multiplex Multiplex may refer to: * Multiplex (automobile), a former American car make * Multiplex (comics), a DC comic book supervillain * Multiplex (company), a global contracting and development company * Multiplex (assay), a biological assay which measu ...
or real-time polymerase chain reaction (qPCR) from extracted ''Salmonella'' DNA. Mathematical models of ''Salmonella'' growth kinetics have been developed for chicken, pork, tomatoes, 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, and are frequently 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, but
UV light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
and heat accelerate their destruction. They perish after being heated to for 90 min, or to for 12 min, although if inoculated in high fat, high liquid substances like peanut butter, they gain heat resistance and can survive up to for 30 min. To protect against ''Salmonella'' infection, heating food to an internal temperature of is recommended. ''Salmonella'' species can be found in the digestive tracts of humans and animals, especially reptiles. ''Salmonella'' on the skin of reptiles or amphibians can be passed to people who handle the animals. Food and water can also be contaminated with the bacteria if they come in contact with the feces of infected people or animals.


Nomenclature

Initially, each ''Salmonella'' "species" was named according to clinical considerations, for example ''Salmonella typhi-murium'' (mouse typhoid fever), ''S. cholerae-suis''. After host specificity was recognized to not exist for many species, new strains received species names according to the location at which the new strain was isolated. Later, molecular findings led to the hypothesis that ''Salmonella'' consisted of only one species, ''S. enterica'', and the serotypes were classified into six groups, two of which are medically relevant. As this now-formalized nomenclature is not in harmony with the traditional usage familiar to specialists in microbiology and infectologists, the traditional nomenclature is still common. Currently, the two recognized species are ''
S. enterica ''Salmonella enterica'' (formerly ''Salmonella choleraesuis'') is a rod-headed, flagellate, facultative anaerobic, Gram-negative bacterium and a species of the genus '' Salmonella''. A number of its serovars are serious human pathogens. Ep ...
'', and '' S. bongori''. In 2005, a third species, ''Salmonella subterranea'', was proposed, but according to the
World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level o ...
, the bacterium reported does not belong in the genus ''Salmonella''. The six main recognised subspecies are: ''enterica'' (serotype I), ''salamae'' (serotype II), ''arizonae'' (IIIa), ''diarizonae'' (IIIb), ''houtenae'' (IV), and ''indica'' (VI). The former serotype V was ''bongori'', which is now considered its own species. The serotype or serovar, is a classification of ''Salmonella'' into subspecies based on antigens that the organism presents. It is based on the Kauffman-White classification scheme that differentiates serological varieties from each other. Serotypes are usually put into subspecies groups after the genus and species, with the serotypes/serovars capitalized, but not italicized: An example is ''Salmonella enterica'' serovar Typhimurium. More modern approaches for typing and subtyping ''Salmonella'' include DNA-based methods such as pulsed field gel electrophoresis, multiple-loci VNTR analysis, multilocus sequence typing, and multiplex- PCR-based methods.


Pathogenicity

''Salmonella'' species are facultative intracellular pathogens. ''Salmonella'' can invade different cell types, including
epithelial cells Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellu ...
, M cells,
macrophage Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...
s, and
dendritic cell Dendritic cells (DCs) are antigen-presenting cells (also known as ''accessory cells'') of the mammalian immune system. Their main function is to process antigen material and present it on the cell surface to the T cells of the immune system. Th ...
s. As facultative anaerobic organism, ''Salmonella'' uses oxygen to make ATP in aerobic environment (i.e., when oxygen is available). However, in anaerobic environment (i.e., when oxygen is not available) ''Salmonella'' produces ATP by
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
; by substituting one or more of four less efficient electron acceptors than oxygen at the end of the electron transport chain: sulfate,
nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...
,
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
, or
fumarate Fumaric acid is an organic compound with the formula HO2CCH=CHCO2H. A white solid, fumaric acid occurs widely in nature. It has a fruit-like taste and has been used as a food additive. Its E number is E297. The salts and esters are known as ...
. Most infections are due to ingestion of food contaminated by animal feces, or by human feces, such as by a food-service worker at a commercial eatery. ''Salmonella'' serotypes can be divided into two main groups—typhoidal and nontyphoidal. Nontyphoidal serotypes are more common, and usually cause self-limiting gastrointestinal disease. They can infect a range of animals, and are zoonotic, meaning they can be transferred between humans and other animals. Typhoidal serotypes include ''Salmonella'' Typhi and ''Salmonella'' Paratyphi A, which are adapted to humans and do not occur in other animals. Molecular modeling and active site analysis of SdiA homolog, a putative quorum sensor for Salmonella typhimurium pathogenecity reveals specific binding patterns of AHL transcriptional regulators. It is also known that Salmonella plasmid virulence gene spvB enhances bacterial virulence by inhibiting autophagy.


Nontyphoidal ''Salmonella''


Non-invasive

Infection with nontyphoidal serotypes of ''Salmonella'' generally results in food poisoning. Infection usually occurs when a person ingests foods that contain a high concentration of the bacteria. Infants and young children are much more susceptible to infection, easily achieved by ingesting a small number of bacteria. In infants, infection through inhalation of bacteria-laden dust is possible. The organisms enter through the digestive tract and must be ingested in large numbers to cause disease in healthy adults. An infection can only begin after living salmonellae (not merely ''Salmonella''-produced toxins) reach the gastrointestinal tract. Some of the microorganisms are killed in the stomach, while the surviving ones enter the small intestine and multiply in tissues. Gastric acidity is responsible for the destruction of the majority of ingested bacteria, but ''Salmonella'' has evolved a degree of tolerance to acidic environments that allows a subset of ingested bacteria to survive. Bacterial colonies may also become trapped in mucus produced in the esophagus. By the end of the incubation period, the nearby host cells are poisoned by endotoxins released from the dead salmonellae. The local response to the endotoxins is enteritis and gastrointestinal disorder. About 2,000 serotypes of nontyphoidal ''Salmonella'' are known, which may be responsible for as many as 1.4 million illnesses in the United States each year. People who are at risk for severe illness include infants, elderly, organ-transplant recipients, and the immunocompromised.


Invasive

While in developed countries, nontyphoidal serotypes present mostly as gastrointestinal disease, in sub-Saharan Africa, these serotypes can create a major problem in bloodstream infections, and are the most commonly isolated bacteria from the blood of those presenting with fever. Bloodstream infections caused by nontyphoidal salmonellae in Africa were reported in 2012 to have a case fatality rate of 20–25%. Most cases of invasive nontyphoidal ''Salmonella'' infection (iNTS) are caused by ''Salmonella enterica'' Typhimurium or ''Salmonella enterica'' Enteritidis. A new form of ''Salmonella'' Typhimurium (ST313) emerged in the southeast of the African continent 75 years ago, followed by a second wave which came out of central Africa 18 years later. This second wave of iNTS possibly originated in the Congo Basin, and early in the event picked up a gene that made it resistant to the antibiotic
chloramphenicol Chloramphenicol is an antibiotic useful for the treatment of a number of bacterial infections. This includes use as an eye ointment to treat conjunctivitis. By mouth or by injection into a vein, it is used to treat meningitis, plague, chole ...
. This created the need to use expensive antimicrobial drugs in areas of Africa that were very poor, making treatment difficult. The increased prevalence of iNTS in sub-Saharan Africa compared to other regions is thought to be due to the large proportion of the African population with some degree of immune suppression or impairment due to the burden of HIV,
malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. ...
, and malnutrition, especially in children. The genetic makeup of iNTS is evolving into a more typhoid-like bacterium, able to efficiently spread around the human body. Symptoms are reported to be diverse, including fever, hepatosplenomegaly, and respiratory symptoms, often with an absence of gastrointestinal symptoms.


Epidemiology

Due to being considered sporadic, between 60% to 80% of salmonella infections cases go undiagnosed. In March 2010, data analysis was completed to estimate an incidence rate of 1140 per 100,000 person-years. In the same analysis, 93.8 million cases of
gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is an inflammation of the gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of energy, and dehydr ...
were due to salmonella infections. At the 5th percentile the estimated amount was 61.8 million cases and at the 95th percentile the estimated amount was 131.6 million cases. The estimated number of deaths due to salmonella was approximately 155,000 deaths. In 2014, in countries such as Bulgaria and Portugal, children under 4 were 32 and 82 times more likely, respectively, to have a salmonella infection. Those who are most susceptible to infection are: children, pregnant women, elderly people, and those with deficient immune systems. Risk factors for Salmonella infections include a variety of foods. Meats such as chicken and pork have the possibility to be contaminated. A variety of vegetables and sprouts may also have salmonella. Lastly, a variety of processed foods such as chicken nuggets and pot pies may also contain this bacteria. Successful forms of prevention come from existing entities such as: the FDA,
United States Department of Agriculture The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of comme ...
, and the Food Safety and Inspection Service. All of these organizations create standards and inspections to ensure public safety in the U.S. For example, the FSIS agency working with the USDA has a Salmonella Action Plan in place. Recently, it received a two-year plan update in February 2016. Their accomplishments and strategies to reduce Salmonella infection are presented in the plans. The
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...
also provides valuable information on preventative care, such has how to safely handle raw foods, and the correct way to store these products. In the
European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are located primarily in Europe, Europe. The union has a total area of ...
, the European Food Safety Authority created preventative measures through risk management and risk assessment. From 2005 to 2009, the EFSA placed an approach to reduce the exposure of salmonella. Their approach included risk assessment and risk management of poultry, which resulted in a reduction of infection cases by one half. In
Latin America Latin America or * french: Amérique Latine, link=no * ht, Amerik Latin, link=no * pt, América Latina, link=no, name=a, sometimes referred to as LatAm is a large cultural region in the Americas where Romance languages — languages derived ...
an orally administered vaccine for Salmonella in poultry developed by Dr. Sherry Layton has been introduced which prevents the bacteria from contaminating the birds. A recent Salmonella Typhimurium outbreak has been linked to chocolate.


Typhoidal ''Salmonella''

Typhoid fever Typhoid fever, also known as typhoid, is a disease caused by '' Salmonella'' serotype Typhi bacteria. Symptoms vary from mild to severe, and usually begin six to 30 days after exposure. Often there is a gradual onset of a high fever over severa ...
is caused by ''Salmonella'' serotypes which are strictly adapted to humans or higher primates—these include ''Salmonella'' Typhi, Paratyphi A, Paratyphi B, and Paratyphi C. In the systemic form of the disease, salmonellae pass through the lymphatic system of the intestine into the blood of the patients (typhoid form) and are carried to various organs (liver, spleen, kidneys) to form secondary foci (septic form). Endotoxins first act on the vascular and nervous apparatus, resulting in increased permeability and decreased tone of the vessels, upset of thermal regulation, and vomiting and diarrhoea. In severe forms of the disease, enough liquid and electrolytes are lost to upset the water-salt metabolism, decrease the circulating blood volume and arterial pressure, and cause
hypovolemic shock Hypovolemic shock is a form of shock caused by severe hypovolemia (insufficient blood volume or extracellular fluid in the body). It could be the result of severe dehydration through a variety of mechanisms or blood loss. Hypovolemic shock is a ...
. Septic shock may also develop. Shock of mixed character (with signs of both hypovolemic and septic shock) is more common in severe salmonellosis. Oliguria and azotemia may develop in severe cases as a result of renal involvement due to hypoxia and toxemia.


Global monitoring

In Germany, food-borne infections must be reported. From 1990 to 2016, the number of officially recorded cases decreased from about 200,000 to about 13,000 cases. In the United States, about 1,200,000 cases of ''Salmonella'' infection are estimated to occur each year. A World Health Organization study estimated that 21,650,974 cases of typhoid fever occurred in 2000, 216,510 of which resulted in death, along with 5,412,744 cases of paratyphoid fever.


Molecular mechanisms of infection

The mechanisms of infection differ between typhoidal and nontyphoidal serotypes, owing to their different targets in the body and the different symptoms that they cause. Both groups must enter by crossing the barrier created by the intestinal cell wall, but once they have passed this barrier, they use different strategies to cause infection.


Switch to virulence

While travelling to their target tissue in the gastrointestinal tract, ''Salmonella'' is exposed to stomach acid, to the detergent-like activity of bile in the intestine, to decreasing oxygen supply, to the competing normal gut flora, and finally to antimicrobial peptides present on the surface of the cells lining the intestinal wall. All of these form stresses that ''Salmonella'' can sense and reacts against, and they form virulence factors and as such regulate the switch from their normal growth in the intestine into
virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ...
. The switch to virulence gives access to a replication
niche Niche may refer to: Science *Developmental niche, a concept for understanding the cultural context of child development * Ecological niche, a term describing the relational position of an organism's species *Niche differentiation, in ecology, the ...
inside the host (such as humans), and can be summarised into several stages: # Approach, in which they travel towards a host cell either via the intestinal
peristalsis Peristalsis ( , ) is a radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an anterograde direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, whi ...
and through active swimming via the flagella, penetrate the mucus barrier, and locate themselves close to the
epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
lining the intestine, # Adhesion, in which they adhere to a host cell using bacterial
adhesins Adhesins are cell-surface components or appendages of bacteria that facilitate adhesion or adherence to other cells or to surfaces, usually in the host they are infecting or living in. Adhesins are a type of virulence factor. Adherence is an essent ...
and a type three-secretion system, # Invasion, in which ''Salmonella'' enter the host cell (see variant mechanisms below), # Replication, in which the bacterium may reproduce inside the host cell, # Spread, in which the bacterium can spread to other organs via cells in the blood (if it succeeded in avoiding the immune defence). Alternatively, bacteria can go back towards the intestine, re-seeding the intestinal population. # Re-invasion (a ''secondary infection'', if now at a systemic site) and further replication.


Mechanisms of entry

Nontyphoidal serotypes preferentially enter M cells on the intestinal wall by bacterial-mediated endocytosis, a process associated with intestinal inflammation and diarrhoea. They are also able to disrupt tight junctions between the cells of the intestinal wall, impairing the cells' ability to stop the flow of ions, water, and immune cells into and out of the intestine. The combination of the inflammation caused by bacterial-mediated endocytosis and the disruption of tight junctions is thought to contribute significantly to the induction of diarrhoea. Salmonellae are also able to breach the intestinal barrier via phagocytosis and trafficking by
CD18 In molecular biology, CD18 (Integrin beta chain-2) is an integrin beta chain protein that is encoded by the ''ITGB2'' gene in humans. Upon binding with one of a number of alpha chains, CD18 is capable of forming multiple heterodimers, which play ...
-positive immune cells, which may be a mechanism key to typhoidal ''Salmonella'' infection. This is thought to be a more stealthy way of passing the intestinal barrier, and may, therefore, contribute to the fact that lower numbers of typhoidal ''Salmonella'' are required for infection than nontyphoidal ''Salmonella''. ''Salmonella'' cells are able to enter
macrophage Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...
s via
macropinocytosis In cellular biology, pinocytosis, otherwise known as fluid endocytosis and bulk-phase pinocytosis, is a mode of endocytosis in which small molecules dissolved in extracellular fluid are brought into the cell through an invagination of the cell me ...
. Typhoidal serotypes can use this to achieve dissemination throughout the body via the mononuclear phagocyte system, a network of connective tissue that contains immune cells, and surrounds tissue associated with the immune system throughout the body. Much of the success of ''Salmonella'' in causing infection is attributed to two type III secretion systems (T3SS) which are expressed at different times during the infection. The T3SS-1 enables the injection of bacterial effectors within the host cytosol. These T3SS-1 effectors stimulate the formation of membrane ruffles allowing the uptake of ''Salmonella'' by nonphagocytic cells. ''Salmonella'' further resides within a membrane-bound compartment called the ''Salmonella''-Containing Vacuole (SCV). The acidification of the SCV leads to the expression of the T3SS-2. The secretion of T3SS-2 effectors by ''Salmonella'' is required for its efficient survival in the host cytosol and establishment of systemic disease. In addition, both T3SS are involved in the colonization of the intestine, induction of intestinal inflammatory responses and diarrhea. These systems contain many genes which must work cooperatively to achieve infection. The AvrA toxin injected by the SPI1 type III secretion system of ''S.'' Typhimurium works to inhibit the
innate immune system The innate, or nonspecific, immune system is one of the two main immunity strategies (the other being the adaptive immune system) in vertebrates. The innate immune system is an older evolutionary defense strategy, relatively speaking, and is the ...
by virtue of its
serine Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − for ...
/ threonine acetyltransferase activity, and requires binding to
eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
target cell
phytic acid Phytic acid is a six-fold dihydrogenphosphate ester of inositol (specifically, of the ''myo'' isomer), also called inositol hexakisphosphate (IP6) or inositol polyphosphate. At physiological pH, the phosphates are partially ionized, resulting ...
(IP6). This leaves the host more susceptible to infection.


Clinical symptoms

Salmonellosis is known to be able to cause back pain or spondylosis. It can manifest as five clinical patterns: gastrointestinal tract infection, enteric fever, bacteremia, local infection, and the chronic reservoir state. The initial symptoms are nonspecific fever, weakness, and myalgia among others. In the bacteremia state, it can spread to any parts of the body and this induces localized infection or it forms abscesses. The forms of localized ''Salmonella'' infections are arthritis, urinary tract infection, infection of the central nervous system, bone infection, soft tissue infection, etc. Infection may remain as the latent form for a long time, and when the function of reticular endothelial cells is deteriorated, it may become activated and consequently, it may secondarily induce spreading infection in the bone several months or several years after acute salmonellosis. A 2018
Imperial College London Imperial College London (legally Imperial College of Science, Technology and Medicine) is a public research university in London, United Kingdom. Its history began with Prince Albert, consort of Queen Victoria, who developed his vision for a cu ...
study also shows how salmonella disrupt specific arms of the
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
(e.g. 3 of 5 NF-kappaB proteins) using a family of zinc metalloproteinase effectors, leaving others untouched. Salmonella thyroid abscess has also been reported.


Resistance to oxidative burst

A hallmark of ''Salmonella'' pathogenesis is the ability of the bacterium to survive and proliferate within phagocytes. Phagocytes produce DNA-damaging agents such as
nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its ...
and oxygen
radicals Radical may refer to: Politics and ideology Politics *Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...
as a defense against pathogens. Thus, ''Salmonella'' species must face attack by molecules that challenge genome integrity. Buchmeier'' et al.'', showed that mutants of ''S. enterica'' lacking RecA or RecBC protein function are highly sensitive to oxidative compounds synthesized by macrophages, and furthermore these findings indicate that successful systemic infection by ''S. enterica'' requires RecA- and RecBC-mediated recombinational repair of DNA damage.


Host adaptation

''S. enterica'', through some of its serotypes such as Typhimurium and Enteritidis, shows signs of the ability to infect several different mammalian host species, while other serotypes such as Typhi seem to be restricted to only a few hosts. Some of the ways that ''Salmonella'' serotypes have adapted to their hosts include loss of genetic material and mutation. In more complex mammalian species,
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
s, which include pathogen specific immune responses, target serovars of ''Salmonella'' through binding of antibodies to structures such as flagella. Through the loss of the genetic material that codes for a flagellum to form, ''Salmonella'' can evade a host's
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
. ''mgtC'' leader RNA from bacteria virulence gene (mgtCBR operon) decreases flagellin production during infection by directly base pairing with mRNAs of the ''fljB'' gene encoding flagellin and promotes degradation. In the study by Kisela ''et al.'', more pathogenic serovars of ''S. enterica'' were found to have certain adhesins in common that have developed out of convergent evolution. This means that, as these strains of ''Salmonella'' have been exposed to similar conditions such as immune systems, similar structures evolved separately to negate these similar, more advanced defenses in hosts. Still, many questions remain about the way that ''Salmonella'' has evolved into so many different types, but ''Salmonella'' may have evolved through several phases. As Baumler ''et al.'' have suggested, ''Salmonella'' most likely evolved through horizontal gene transfer, formation of new serovars due to additional
pathogenicity island Pathogenicity islands (PAIs), as termed in 1990, are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer. Pathogenicity islands are found in both animal and plant pathogens. Additionally, PAIs are found i ...
s. and an approximation of its ancestry. So, ''Salmonella'' could have evolved into its many different serotypes through gaining genetic information from different pathogenic bacteria. The presence of several
pathogenicity island Pathogenicity islands (PAIs), as termed in 1990, are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer. Pathogenicity islands are found in both animal and plant pathogens. Additionally, PAIs are found i ...
s in the genome of different serotypes has lent credence to this theory. ''Salmonella'' sv. Newport has signs of adaptation to a plant colonization lifestyle, which may play a role in its disproportionate association with foodborne illness linked to produce. A variety of functions selected for during sv. Newport persistence in tomatoes have been reported to be similar to those selected for in sv. Typhimurium from animal hosts. The ''papA'' gene, which is unique to sv. Newport, contributes to the strain's fitness in tomatoes, and has homologs in genomes of other Enterobacteriaceae that are able to colonize plant and animal hosts.


Research

In addition to their importance as pathogens, nontyphoidal Salmonella species such as ''S. enterica'' serovar Typhimurium are commonly used as homologues of typhoid species. Many findings are transferable and it attenuates the danger for the researcher in case of contamination, but is also limited. For example, it is not possible to study specific typhoidal toxins using this model. However, strong research tools such as the commonly-used mouse intestine
gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is an inflammation of the gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of energy, and dehydr ...
model build upon the use of ''Salmonella'' Typhimurium. For
genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar work ...
, ''S.'' Typhimurium has been instrumental in the development of genetic tools that led to an understanding of fundamental bacterial physiology. These developments were enabled by the discovery of the first generalized transducing phage P22 in ''S''. Typhimurium, that allowed quick and easy
genetic editing Genetic editing (French ''critique génétique''; German ''genetische Kritik'') is an approach to scholarly editing in which an exemplar is seen as derived from a dossier of other manuscripts and events. The derivation can be through physical cut ...
. In turn, this made fine structure genetic analysis possible. The large number of mutants led to a revision of genetic nomenclature for bacteria. Many of the uses of transposons as genetic tools, including transposon delivery, mutagenesis, and construction of chromosome rearrangements, were also developed in ''S''. Typhimurium. These genetic tools also led to a simple test for carcinogens, the Ames test. As a natural alternative to traditional antimicrobials, phages are being recognised as highly effective control agents for Salmonella and other foodborne bacteria.


Ancient DNA

''S. enterica'' genomes have been reconstructed from up to 6,500 year old human remains across Western Eurasia, which provides evidence for geographic widespread infections with systemic ''S. enterica'' during prehistory, and a possible role of the Neolithization process in the evolution of host adaptation. Additional reconstructed genomes from colonial Mexico suggest ''S. enterica'' as the cause of ''
cocoliztli The Cocoliztli Epidemic or the Great Pestilence was an outbreak of a mysterious illness characterized by high fevers and bleeding which caused millions of deaths in New Spain during the 16th-century. The Aztec people called it ''cocoliztli'', Na ...
'', an epidemic in 16th-century
New Spain New Spain, officially the Viceroyalty of New Spain ( es, Virreinato de Nueva España, ), or Kingdom of New Spain, was an integral territorial entity of the Spanish Empire, established by Habsburg Spain during the Spanish colonization of the A ...
.


See also

*
1984 Rajneeshee bioterror attack In 1984, 751 people suffered food poisoning in The Dalles, Oregon, United States, due to the deliberate contamination of salad bars at ten local restaurants with ''Salmonella''. A group of prominent followers of Rajneesh (later known as Os ...
* The Great Hormel Disaster of '98 *
2008 United States salmonellosis outbreak The 2008 United States salmonellosis outbreak was an outbreak of salmonellosis across multiple U.S. states due to ''Salmonella enterica'' serovar Saintpaul. Over the course of the outbreak, 1442 cases were identified across 43 U.S. states, the D ...
* '' American Public Health Association v. Butz'' * Bismuth sulfite agar *
Food testing strips Food testing strips are products that help determine whether or not food contains bacteria that can cause foodborne illness. These products can typically be used on food, water, and hard surfaces, and are often designed for quick and easy home and ...
* Host-pathogen interface *
List of foodborne illness outbreaks This is a list of foodborne illness outbreaks. A foodborne illness may be from an infectious disease, heavy metals, chemical contamination, or from natural toxins, such as those found in poisonous mushrooms. Deadliest * List of foodborne illness ...
* 2008–2009 peanut-borne salmonellosis *
Wright County Egg Wright County Egg (formerly DeCoster Egg Farms), based in Galt, Iowa, is one of the top ten poultry farms in the United States, with a flock of more than 15 million chickens. The company also produces pork. History The company was founded by Aus ...
* XLD agar


References


External links


Background on Salmonella
from th
Food Safety and Inspection Service
of th
United States Department of Agriculture

Salmonella
genomes and related information a
PATRIC
a Bioinformatics Resource Center funded b
NIAID

Questions and Answers about commercial and institutional sanitizing methods

Symptoms of Salmonella Poisoning

''Salmonella'' as an emerging pathogen
from IFAS
Notes on ''Salmonella'' nomenclature


video
Avian Salmonella


nbsp;— The Merck Veterinary Manual {{authority control Gram-negative bacteria Pathogenic bacteria Tropical diseases Zoonoses Rodent-carried diseases Bacteria genera Biological anti-agriculture weapons