Salmonella enterica

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Salmonella enterica
Salmonella enterica serovar typhimurium 01.jpg
S. enterica Typhimurium colonies on a Hektoen enteric agar plate
Scientific classification Red Pencil Icon.png
Domain: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Enterobacteriales
Family: Enterobacteriaceae
Genus: Salmonella
S. enterica
Binomial name
Salmonella enterica
(ex Kauffmann & Edwards 1952) Le Minor & Popoff 1987

Salmonella enterica (formerly Salmonella choleraesuis) is a rod-shaped, flagellate, facultative aerobic, Gram-negative bacterium and a species of the genus Salmonella . [1] A number of its serovars are serious human pathogens.

Bacillus (shape) rod-shaped bacterium (not to be confused with the taxon Bacilli)

A bacillus or bacilliform bacterium is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name Bacillus, capitalized and italicized, refers to a specific genus of bacteria. The name Bacilli, capitalized but not italicized, can also refer to a less specific taxonomic group of bacteria that includes two orders, one of which contains the genus Bacillus. When the word is formatted with lowercase and not italicized, 'bacillus', it will most likely be referring to shape and not to the genus at all. Bacilliform bacteria are also often simply called rods when the bacteriologic context is clear. Sea Bacilli usually divide in the same plane and are solitary, but can combine to form diplobacilli, streptobacilli, and palisades.

Flagellate cell or organism

A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word flagellate also describes a particular construction characteristic of many prokaryotes and eukaryotes and their means of motion. The term presently does not imply any specific relationship or classification of the organisms that possess flagellae. However, the term "flagellate" is included in other terms which are more formally characterized.

Facultative anaerobic organism organism that makes ATP by aerobic respiration if oxygen is present

A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.



Most cases of salmonellosis are caused by food infected with S. enterica, which often infects cattle and poultry, though other animals such as domestic cats [2] [ citation needed ] and hamsters [3] have also been shown to be sources of infection in humans. Investigations of vacuum cleaner bags have shown that households can act as a reservoir of the bacterium; this is more likely if the household has contact with an infection source (i.e., members working with cattle or in a veterinary clinic).

Hamster subfamily of mammals

Hamsters are rodents belonging to the subfamily Cricetinae, which contains 18 species classified in seven genera. They have become established as popular small house pets. The best-known species of hamster is the golden or Syrian hamster, which is the type most commonly kept as pets. Other hamster species commonly kept as pets are the three species of dwarf hamster, Campbell's dwarf hamster, the winter white dwarf hamster and the Roborovski hamster.

Vacuum cleaner device to suck up dirt

A vacuum cleaner, also known as a sweeper or hoover, is a device that uses an air pump, to create a partial vacuum to suck up dust and dirt from floors and from other surfaces such as upholstery and draperies.

Raw chicken eggs and goose eggs can harbor S. enterica, initially in the egg whites, although most eggs are not infected. As the egg ages at room temperature, the yolk membrane begins to break down and S. enterica can spread into the yolk. Refrigeration and freezing do not kill all the bacteria, but substantially slow or halt their growth. Pasteurizing and food irradiation are used to kill Salmonella for commercially produced foodstuffs containing raw eggs such as ice cream. Foods prepared in the home from raw eggs, such as mayonnaise, cakes, and cookies, can spread salmonellae if not properly cooked before consumption.

Pasteurization or pasteurisation is a process in which certain packaged and non-packaged foods are treated with mild heat, usually less than 100 °C (212 °F), to eliminate pathogens and extend shelf life. The process is intended to stabilize foods by destroying or inactivating organisms and enzymes that contribute to spoilage, including vegetative bacteria but not bacterial spores. Since Pasteurization is not sterilization, and does not kill spores, a second "double" pasteurization will extend the quality by killing spores that have germinated.

Food irradiation Sterilization of food with ionizing radiations for enhanced preservation and longer shelflife

Food irradiation is the process of exposing food and food packaging to ionizing radiation. Ionizing radiation, such as from gamma rays, x-rays, or electron beams, is energy that can be transmitted without direct contact to the source of the energy (radiation) capable of freeing electrons from their atomic bonds (ionization) in the targeted food. The radiation can be emitted by a radioactive substance or generated electrically. This treatment is used to improve food safety by extending product shelf-life (preservation), reducing the risk of foodborne illness, delaying or eliminating sprouting or ripening, by sterilization of foods, and as a means of controlling insects and invasive pests. Food irradiation primarily extends the shelf-life of irradiated foods by effectively destroying organisms responsible for spoilage and foodborne illness and inhibiting sprouting.

S. enterica was possibly the cause of cocoliztli , an epidemic in 16th-century New Spain. [4]

New Spain viceroyalty of the Spanish Empire (1535-1821)

The Viceroyalty of New Spain was an integral territorial entity of the Spanish Empire, established by Habsburg Spain during the Spanish colonization of the Americas. It covered a huge area that included territories in North America, South America, Asia and Oceania. It originated in 1521 after the fall of Mexico-Tenochtitlan, the main event of the Spanish conquest, which did not properly end until much later, as its territory continued to grow to the north. It was officially created on 8 March 1535 as a viceroyalty, the first of four viceroyalties Spain created in the Americas. Its first viceroy was Antonio de Mendoza y Pacheco, and the capital of the viceroyalty was Mexico City, established on the ancient Mexico-Tenochtitlan.


Secreted proteins are of major importance for the pathogenesis of infectious diseases caused by S. enterica. A remarkably large number of fimbrial and nonfimbrial adhesins are present in Salmonella, and mediate biofilm formation and contact to host cells. Secreted proteins are also involved in host-cell invasion and intracellular proliferation, two hallmarks of Salmonella pathogenesis. [5]

Fimbria (bacteriology)

In bacteriology, a fimbria, also referred to as an "attachment pilus" by some scientists, is an appendage that can be found on many Gram-negative and some Gram-positive bacteria that is thinner and shorter than a flagellum. This appendage ranges from 3-10 nanometers in diameter and can be up to several micrometers long. Fimbriae are used by bacteria to adhere to one another and to adhere to animal cells and some inanimate objects. A bacterium can have as many as 1,000 fimbriae. Fimbriae are only visible with the use of an electron microscope. They may be straight or flexible.

Adhesins are cell-surface components or appendages of bacteria that facilitate adhesion or adherence to other cells or to surfaces, usually the host they are infecting or living in. Adhesins are a type of virulence factor.

Biofilm any group of microorganisms in which cells stick to each other and often also to a surface (adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular polymeric substances)

A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular polymeric substances (EPS). The cells within the biofilm produce the EPS components, which are typically a polymeric conglomeration of extracellular polysaccharides, proteins, lipids and DNA. Because they have three-dimensional structure and represent a community lifestyle for microorganisms, they have been metaphorically described as "cities for microbes".

Small noncoding RNA

Small nonprotein-coding RNAs (sRNA) are able to perform specific functions without being translated into proteins; 97 bacterial sRNAs from Salmonella Typhi were discovered. [6]

Bacterial small RNAs (sRNA) are small RNAs produced by bacteria; they are 50- to 500-nucleotide non-coding RNA molecules, highly structured and containing several stem-loops. Numerous sRNAs have been identified using both computational analysis and laboratory-based techniques such as Northern blotting, microarrays and RNA-Seq in a number of bacterial species including Escherichia coli, the model pathogen Salmonella, the nitrogen-fixing alphaproteobacterium Sinorhizobium meliloti, marine cyanobacteria, Francisella tularensis, Streptococcus pyogenes, the pathogen Staphylococcus aureus, and the plant pathogen Xanthomonas oryzae pathovar oryzae. Bacterial sRNAs affect how genes are expressed within bacterial cells via interaction with mRNA or protein, and thus can affect a variety of bacterial functions like metabolism, virulence, environmental stress response, and structure.

AsdA (antisense RNA of dnaA) is a cis-encoded antisense RNA of dnaA described in S. enterica serovar Typhi. It was discovered by deep sequencing and its transcription was confirmed by Northern blot and RACE analysis. AsdA is estimated to be about 540 nucleotides long, and represents the complementary strand to that encoding DnaA, a protein that plays a central role in the initiation of DNA replication and hence cellular division. In rich media, it is highly expressed only after reaching the stationary growth phase, but under limiting iron or osmotic stress, it is already expressed during exponential growth. Overexpression of AsdA stabilizes dnaA mRNA, increasing its levels and thereby enhancing its rate of translation. This suggests that AsdA is a regulator of DNA replication. [7]


S. enterica has six subspecies, and each subspecies has associated serovars that differ by antigenic specificity. [8] S. enterica has over 2500 serovars. [9] Salmonella bongori was previously considered a subspecies of S. enterica, but it is now the other species in the genus Salmonella. Most of the human pathogenic Salmonella serovars belong to the enterica subspecies. These serogroups include S. Typhi, S. Enteritidis, S. Paratyphi, S. Typhimurium, and S. Choleraesuis. The serovars can be designated as written in the previous sentence (capitalized and nonitalicized following the genus), or as follows: "S. enterica subsp. enterica, serovar Typhi".

See also

Related Research Articles

<i>Salmonella</i> Genus of prokaryotes

Salmonella is a genus of rod-shaped (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 and is further divided into six subspecies that include over 2,600 serotypes.

Transduction (genetics) The transfer of genetic information to a bacterium from a bacteriophage or between bacterial or yeast cells mediated by a phage vector.

Transduction is the process by which foreign DNA is introduced into a cell by a virus or viral vector. An example is the viral transfer of DNA from one bacterium to another and hence an example of horizontal gene transfer. Transduction does not require physical contact between the cell donating the DNA and the cell receiving the DNA, and it is DNase resistant. Transduction is a common tool used by molecular biologists to stably introduce a foreign gene into a host cell's genome.

Salmonellosis infection caused by Salmonella bacteria

Salmonellosis is a symptomatic infection caused by bacteria of the Salmonella type. The most common symptoms are diarrhea, fever, abdominal cramps, and vomiting. Symptoms typically occur between 12 hours and 36 hours after exposure, and last from two to seven days. Occasionally more significant disease can result in dehydration. The old, young, and others with a weakened immune system are more likely to develop severe disease. Specific types of Salmonella can result in typhoid fever or paratyphoid fever.

Serotype infraspecific name

A serotype or serovar is a distinct variation within a species of bacteria or virus or among immune cells of different individuals. These microorganisms, viruses, or cells are classified together based on their cell surface antigens, allowing the epidemiologic classification of organisms to the sub-species level. A group of serovars with common antigens is called a serogroup or sometimes serocomplex.

Enterobacteria phage P22 is a bacteriophage in the Podoviridae family that infects Salmonella typhimurium. Like many phages, it has been used in molecular biology to induce mutations in cultured bacteria and to introduce foreign genetic material. P22 has been used in generalized transduction and is an important tool for investigating Salmonella genetics.

fis is an E. coli gene encoding the Fis protein. The regulation of this gene is more complex than most other genes in the E. coli genome, as Fis is an important protein which regulates expression of other genes. It is supposed that fis is regulated by H-NS, IHF and CRP. It also regulates its own expression (autoregulation). Fis is one of the most abundant DNA binding proteins in Escherichia coli under nutrient-rich growth conditions.


A retron is a distinct DNA sequence found in the genome of many bacteria species that codes for reverse transcriptase and a unique single-stranded DNA/RNA hybrid called multicopy single-stranded DNA (msDNA). Retron msr RNA is the non-coding RNA produced by retron elements and is the immediate precursor to the synthesis of msDNA. The retron msr RNA folds into a characteristic secondary structure that contains a conserved guanosine residue at the end of a stem loop. Synthesis of DNA by the retron-encoded reverse transcriptase (RT) results in a DNA/RNA chimera which is composed of small single-stranded DNA linked to small single-stranded RNA. The RNA strand is joined to the 5' end of the DNA chain via a 2'-5' phosphodiester linkage that occurs from the 2' position of the conserved internal guanosine residue.


The SraB RNA is a small non-coding RNA discovered in E. coli during a large scale experimental screen. The 14 novel RNAs discovered were named 'sra' for small RNA, examples include SraC, SraD and SraG. This ncRNA was found to be expressed only in stationary phase. The exact function of this RNA is unknown but it has been shown to affect survival of Salmonella enterica to antibiotic administration in egg albumin. The authors suggest this may be due to SraB regulating a response to components in albumin.


The MicA RNA is a small non-coding RNA that was discovered in E. coli during a large scale screen. Expression of SraD is highly abundant in stationary phase, but low levels could be detected in exponentially growing cells as well.

Hfq protein

The Hfq protein encoded by the hfq gene was discovered in 1968 as an Escherichia coli host factor that was essential for replication of the bacteriophage Qβ. It is now clear that Hfq is an abundant bacterial RNA binding protein which has many important physiological roles that are usually mediated by interacting with Hfq binding sRNA.

Leucine responsive protein, or Lrp, is a global regulator protein, meaning that it regulates the biosynthesis of leucine, as well as the other branched-chain amino acids, valine and isoleucine. In bacteria, it is encoded by the lrp gene.

Bacterial microcompartment


Pasteurized eggs

Pasteurized eggs are eggs that have been pasteurized in order to reduce the risk of food-borne illness in dishes that are not cooked or are only lightly cooked. They may be sold as liquid egg products or pasteurized in the shell.

<i>Salmonella enterica</i> subsp. <i>enterica</i> subspecies of bacterium

Salmonella enterica subsp. enterica is a subspecies of Salmonella enterica, the rod-shaped, flagellated, aerobic, Gram-negative bacterium. Many of the pathogenic serovars of the S. enterica species are in this subspecies, including that responsible for typhoid.

Bacterial DNA binding protein

In molecular biology, bacterial DNA binding proteins are a family of small, usually basic proteins of about 90 residues that bind DNA and are known as histone-like proteins. Since bacterial binding proteins have a diversity of functions, it has been difficult to develop a common function for all of them. They are commonly referred to as histone-like and have many similar traits with the eukaryotic histone proteins. Eukaryotic histones package DNA to help it to fit in the nucleus, and they are known to be the most conserved proteins in nature. Examples include the HU protein in Escherichia coli, a dimer of closely related alpha and beta chains and in other bacteria can be a dimer of identical chains. HU-type proteins have been found in a variety of eubacteria and archaebacteria, and are also encoded in the chloroplast genome of some algae. The integration host factor (IHF), a dimer of closely related chains which is suggested to function in genetic recombination as well as in translational and transcriptional control is found in Enterobacteria and viral proteins including the African swine fever virus protein A104R.

Salmonella bongori is a pathogenic bacterium belonging to the genus Salmonella, and was earlier known as Salmonella subspecies V or S. enterica subsp. bongori or S. choleraesuis subsp. bongori. It is a Gram-negative, rod-shaped bacterium (bacillus), which causes a gastrointestinal disease called salmonellosis, characterized by cramping and diarrhoea. It is typically considered a microbe of cold-blooded animals, unlike other members of the genus, and is most frequently associated with reptiles.

Fructose-asparagine chemical compound

Fructose-asparagine is a glycosylamine compound that is used during Salmonella-mediated inflammation of the intestine. The name of the genetic locus that encodes the uptake capability in Salmonella is fra. This fra locus has five genes: fraR, fraB a fructose-asparagine deglycase, fraD a sugar kinase, fraA a fructose-asparagine transporter, and fraE a L-asparaginase.

Salmonellosis annually causes, per CDC estimation, about 1.2 million illnesses, 23,000 hospitalizations, and 450 deaths in the United States every year.

AsrC small RNA

AsrC is a cis-encoded antisense RNA of rseC described in Salmonella enterica serovar Typhi. It was discovered by deep sequencing and its transcription was confirmed by Northern blot. AsrC is an 893 bp sequence that covers all of the rseC coding region in the reverse direction of transcription. It increases the level of rseC mRNA and protein, indirectly activating RpoE. RpoE can promote flagellar gene expression and motility. Coincidently, expression of AsrC increased bacterial swimming motility. it is possible that it is because AsrC is promoting the expression of genes related to motility.

IsrM small RNA

The IsrM RNA is a small non-coding RNA discovered in Salmonella pathogenicity island, which is not found in E.coli. It is important for invasion of epithelial cells, intracellular replication inside macrophages, virulence and colonisation in mice. It targets the SopA and HilE mRNAs, virulence factors essential for bacterial invasion. It is a first pathogenicity island-encoded sRNA shown to be directly involved in Salmonella pathogenesis.


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