''Salmonella enterica'' subsp. ''enterica'' is a

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 ...

of ''

Salmonella 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. Epidemi ...

'', the rod-shaped,

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...

ted, aerobic,

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 ...

. Many of the pathogenic

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 of the ''S. enterica'' species are in this subspecies, including that responsible for

typhoid 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 several d ...

Serovars

''S. enterica'' subsp. ''enterica'' contains a large number of serovars which can infect a broad range of

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...

hosts. The individual members range from being highly host-adapted (only able to infect a narrow range of species) to displaying a broad host range. A number of techniques are currently used to differentiate between

serotype 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. These include looking for the presence or absence of

antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune respon ...

phage typing Phage typing is a phenotypic method that uses bacteriophages ("phages" for short) for detecting and identifying single strains of bacteria. Phages are viruses that infect bacteria and may lead to bacterial cell lysis. The bacterial strain is assi ...

, molecular fingerprinting and biotyping, where serovars are differentiated by which nutrients they are able to ferment. A possible factor in determining the host range of particular serovars is phage-mediated acquisition of a small number of genetic elements that enable infection of a particular host. It is further postulated that serovars which infect a narrow range of species have diverged from ancestors with a broad host range, and have since specialised and lost the ability to infect some hosts. A selection of serovars, with known hosts listed. Since there are more than 2500 serovars of ''Salmonella enterica'' subsp. ''enterica'', this list is incomplete. A study of data from 37 countries collected between 2001 and 2007 found that the most common serovar of ''Salmonella'' isolated from human cases was Enteritidis, found in an average of 43.5% of cases, followed by Typhimurium (17.1% of cases), Newport (3.5%), Infantis (1.8%), Virchow (1.5%), Hadar (1.5%), and Agona (0.8%). One strain of ''Salmonella'' that has recently been emerging in the United States is ''S. enterica'' ser. Javiana. "An outbreak occurred in 2002, there were 141 cases that occurred among the participants of the U.S. Transplant Games. Out of the 141 cases, most of the cases were either transplant recipients (34%) or people receiving immunosuppressive therapy (32%)". There is an increasing number of ''Salmonella'' serotypes that are multidrug resistant (MDR), which was identified by the

CDC 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 ...

's National Antimicrobial Resistance Monitoring System. "''Salmonella''Javiana causes 4% of non-typhodial ''Salmonella'' infections in the United States each year." In November 2016, a new strain of extensively drug resistant (XDR) ''Salmonella enterica'' serovar Typhi emerged in Pakistan, primarily from the cities of

Hyderabad Hyderabad ( ; , ) is the capital and largest city of the Indian state of Telangana and the ''de jure'' capital of Andhra Pradesh. It occupies on the Deccan Plateau along the banks of the Musi River, in the northern part of Southern Indi ...

and

Karachi Karachi (; ur, ; ; ) is the most populous city in Pakistan and 12th most populous city in the world, with a population of over 20 million. It is situated at the southern tip of the country along the Arabian Sea coast. It is the former c ...

. Multidrug resistant strains have been present since the late 1970s in Africa and Asia. These XDR strains are resistant to all antibiotic treatment options:

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 ...

ampicillin Ampicillin is an antibiotic used to prevent and treat a number of bacterial infections, such as respiratory tract infections, urinary tract infections, meningitis, salmonellosis, and endocarditis. It may also be used to prevent group B str ...

, trimethoprim-sulfamethoxazole, fluoroquinolones, and third-generation cephalosporins. The outbreak has been ongoing since 2016.

Metabolism

Genetic evidence suggests that the serovars can be divided into two groups – one which causes enteric infection and has a broad repertoire of metabolic capabilities, and one which usually causes invasive infection, often in a narrow range of hosts, and shows degradation of

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...

metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical ...

s. It is thought that these metabolic capabilities are important for obtaining nutrients in the challenging and nutrient-limited inflamed gut environment.

Nomenclature

The serovars can be designated fully or in a shortened form. The short form lists the genus, ''Salmonella'', which is followed by the capitalized not italicized serovar, e.g. ''Salmonella'' Typhi whereas, full designation for ''Salmonella'' Typhi is ''Salmonella enterica'' subsp. ''enterica'' serovar Typhi. Each serovar can have many strains, as well, which allows for a rapid increase in the total number of antigenically variable bacteria.

Epidemiology

Invasive strains of non-typhoidal ''Salmonella'', such as ''Salmonella'' Typhimurium ST313 have recently been labelled as causing emerging diseases in Africa. Key host

immune deficiencies Immunodeficiency, also known as immunocompromisation, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that a ...

associated with 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 have contributed to a wide spread of this disease and the need to use expensive

antimicrobial drugs An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria, and antifungals a ...

in the poorest health services in the world. But also bacterial factors, such as upregulated activity of the virulence gene ''pgtE'', due to a

single nucleotide polymorphism In genetics, a single-nucleotide polymorphism (SNP ; plural SNPs ) is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently larg ...

(SNP) in its promoter region, have been shown to have a great impact upon the pathogenesis of this particular ''Salmonella'' sequence type.

References

{{DEFAULTSORT:Salmonella Enterica Enterica Salmonella Typhoid fever Infectious causes of cancer Subspecies