''Salmonella enterica'' (formerly ''Salmonella choleraesuis'') is a rod-headed,

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and thei ...

facultative anaerobic A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...

bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

and a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

of the

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 ...

Salmonella ''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 ...

''. A number of its

serovar 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 surface antigens, allowing the ep ...

s are serious human

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a g ...

Epidemiology

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 and

hamster Hamsters are rodents (order Rodentia) belonging to the subfamily Cricetinae, which contains 19 species classified in seven genera.Fox, Sue. 2006. ''Hamsters''. T.F.H. Publications Inc. They have become established as popular small pets. The ...

s have also been shown to be sources of infection in humans. Investigations of

vacuum cleaner A vacuum cleaner, also known simply as a vacuum or a hoover, is a device that causes suction in order to remove dirt from floors, upholstery, draperies, and other surfaces. It is generally electrically driven. The dirt is collected by either a ...

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 Veterinary medicine is the branch of medicine that deals with the prevention, management, diagnosis, and treatment of disease, disorder, and injury in animals. Along with this, it deals with animal rearing, husbandry, breeding, research on nutri ...

). Raw chicken eggs and goose eggs can harbor ''S. enterica'', initially in the

egg white Egg white is the clear liquid (also called the albumen or the glair/glaire) contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms ar ...

s, 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 Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example ...

. Refrigeration and freezing do not kill all the bacteria, but substantially slow or halt their growth.

Pasteurizing Pasteurization or pasteurisation is a process of food preservation in which packaged and non-packaged foods (such as milk and fruit juices) are treated with mild heat, usually to less than , to eliminate pathogens and extend shelf life. Th ...

and

food irradiation Food irradiation is the process of exposing food and food packaging to ionizing radiation, such as from gamma rays, x-rays, or electron beams. Food irradiation improves food safety and extends product shelf life (preservation) by effective ...

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 Mayonnaise (; ), colloquially referred to as "mayo" , is a thick, cold, and creamy sauce or dressing commonly used on sandwiches, hamburgers, composed salads, and French fries. It also forms the base for various other sauces, such as tarta ...

, cakes, and cookies, can spread salmonellae if not properly cooked before consumption. ''S. enterica'' genomes have been reconstructed from up 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 The Neolithic Revolution, or the (First) Agricultural Revolution, was the wide-scale transition of many human cultures during the Neolithic period from a lifestyle of hunting and gathering to one of agriculture and settlement, making an incr ...

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 ...

Pathogenesis

Secreted proteins are of major importance for the

pathogenesis Pathogenesis is the process by which a disease or disorder develops. It can include factors which contribute not only to the onset of the disease or disorder, but also to its progression and maintenance. The word comes from Greek πάθος ''pat ...

of infectious diseases caused by ''S. enterica''. A remarkably large number of fimbrial and nonfimbrial adhesins are present in ''Salmonella'', and mediate

biofilm 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 po ...

formation and contact to host cells. Secreted proteins are also involved in host-cell invasion and intracellular proliferation, two hallmarks of ''Salmonella'' pathogenesis.

DNA repair capability

Exposure of ''S. enterica'' to bile salts, such as sodium deoxycholate, induces the SOS DNA damage response indicating that in this organism bile salts cause

DNA damage DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA d ...

.Prieto AI, Ramos-Morales F, Casadesús J. Repair of DNA damage induced by bile salts in Salmonella enterica. Genetics. 2006 Oct;174(2):575-84. doi: 10.1534/genetics.106.060889. Epub 2006 Aug 3. PMID: 16888329; PMCID: PMC1602091 Bile salt exposure is found to increase GC to AT transition mutations and also to induce genes of the OxyR and SoxRS regulons suggesting further that bile salts specifically cause oxidative DNA damage. Mutants of ''S. enterica'' that are defective in enzymes required for the process of

base excision repair Base excision repair (BER) is a cellular mechanism, studied in the fields of biochemistry and genetics, that repairs damaged DNA throughout the cell cycle. It is responsible primarily for removing small, non-helix-distorting base lesions from ...

are sensitive to bile salts. This indicates that wild-type ''S. enterica'' uses base excision repair to remove DNA damages caused by the bile salts. The

RecBCD Exodeoxyribonuclease V (EC 3.1.11.5, RecBCD, Exonuclease V, ''Escherichia coli'' exonuclease V, ''E. coli'' exonuclease V, gene recBC endoenzyme, RecBC deoxyribonuclease, gene recBC DNase, gene recBCD enzymes) is an enzyme of ''E. coli'' that ini ...

enzyme which functions in recombinational repair of DNA is also required for bile salt resistance.

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. AsdA (antisense RNA of dnaA) is a ''cis-''encoded

antisense RNA Antisense RNA (asRNA), also referred to as antisense transcript, natural antisense transcript (NAT) or antisense oligonucleotide, is a single stranded RNA that is complementary to a protein coding messenger RNA (mRNA) with which it hybridizes, and ...

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

nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecu ...

s 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.

Nomenclature

''S. enterica'' has six subspecies, and each subspecies has associated

s that differ by antigenic specificity. ''S. enterica'' has over 2500 serovars. '' 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 In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...

''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".

References

External links

Notes on ''Salmonella'' nomenclature
*
Current research on ''Salmonella typhimurium '' at the Norwich Research Park
*
Type strain of ''Salmonella enterica'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q2264864 Salmonella Gram-negative bacteria Typhoid fever