Salmonella enterica subsp. enterica

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.[1]

Salmonella enterica subsp. enterica
Salmonella Typhimurium colonies on a Hektoen enteric agar plate
Scientific classification
Domain:
Bacteria
Phylum:
Proteobacteria
Class:
Gammaproteobacteria
Order:
Enterobacterales
Family:
Enterobacteriaceae
Genus:
Salmonella
Species:
S. enterica
Subspecies:
S. enterica subsp. enterica
Serovars
  • Salmonella Choleraesuis
  • Salmonella Dublin
  • Salmonella Enteritidis
  • Salmonella Heidelberg
  • Salmonella Paratyphi
  • Salmonella Typhi
  • Salmonella Typhimurium

Serovars

S. enterica subsp. enterica contains a large number of serovars which can infect a broad range of vertebrate 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 serotypes. These include looking for the presence or absence of antigens, phage typing, 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.[2] 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.[3]

A selection of serovars, with known hosts listed. Since there are more than 2500 serovars of Salmonella enterica subsp. enterica, this list is incomplete.

SerovarHost species
Salmonella CholeraesuisSwine
Salmonella DublinCattle
Salmonella EnteritidisHumans, rodents, galliformes
Salmonella GallinarumGalliformes
Salmonella HadarHumans, galliformes, rabbits
Salmonella HeidelbergHumans, galliformes, swine[4]
Salmonella InfantisHumans, poultry
Salmonella ParatyphiHumans
Salmonella TyphiHumans
Salmonella TyphimuriumHumans, cattle, swine, sheep, horses, rodents, galliformes

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%).[5]

One strain of Salmonella that has recently been emerging in the United States is Salmonella 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's National Antimicrobial Resistance Monitoring System.[6] "Salmonella javiana causes 4% of nontyphodial Salmonella infections in the United States each year."[7]

In November 2016, a new strain of extensively drug resistant (XDR) Salmonella enterica serovar Typhi emerged in Pakistan, primarily from the cities of Hyderabad and Karachi.[8] Multidrug resistant strains have been present since the late 1970s in Africa and Asia.[9] These XDR strains are resistant to all antibiotic treatment options: chloramphenicol, ampicillin, trimethoprim-sulfamethoxazole, fluoroquinolones, and third-generation cephalosporins. The outbreak has been ongoing since 2016.[10]

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 metabolic pathways. It is thought that these metabolic capabilities are important for obtaining nutrients in the challenging and nutrient-limited inflamed gut environment.[11]

Nomenclature

The serovars can be designated fully or in a shortened form.[12] The short form lists the genus, Salmonella, which is followed by the capitalized and non-italicized serovar. The full designation for Salmonella Typhi is Salmonella enterica subsp. enterica, serovar Typhi.[13] Each serovar can have many strains, as well, which allows for a rapid increase in the total number of antigenically variable bacteria.[14]

Epidemiology
Main article: Salmonellosis

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 associated with HIV, malaria and malnutrition have contributed to a wide spread of this disease and the need to use expensive antimicrobial drugs in the poorest health services in the world.[15] But also bacterial factors, such as upregulated activity of the virulence gene pgtE, due to a single nucleotide polymorphism (SNP) in its promoter region, have been shown to have a great impact upon the pathogenesis of this particular Salmonella sequence type.[16]

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References
  1. Murray PR, Rosenthal KS, Pfaller MA (2009). Medical Microbiology (6th ed.). Philadelphia, PA: Mosby Elsevier. p. 307.
  2. Sternlicht M, Staaby J, Sullivan I (December 1975). "Birth order, maternal age, and mental retardation". Mental Retardation. 13 (6): 3–6. doi:10.1128/IAI.70.5.2249-2255.2002. PMC 127920. PMID 11953356.
  3. Langridge GC, Fookes M, Connor TR, Feltwell T, Feasey N, Parsons BN, Seth-Smith HM, Barquist L, Stedman A, Humphrey T, Wigley P, Peters SE, Maskell DJ, Corander J, Chabalgoity JA, Barrow P, Parkhill J, Dougan G, Thomson NR (January 2015). "Patterns of genome evolution that have accompanied host adaptation in Salmonella". Proceedings of the National Academy of Sciences of the United States of America. 112 (3): 863–8. Bibcode:2015PNAS..112..863L. doi:10.1073/pnas.1416707112. PMC 4311825. PMID 25535353.
  4. "Snapshots of Salmonella Serotypes" (PDF). Centers for Disease Control and Prevention. CDC.
  5. Hendriksen RS, Vieira AR, Karlsmose S, Lo Fo Wong DM, Jensen AB, Wegener HC, Aarestrup FM (August 2011). "Global monitoring of Salmonella serovar distribution from the World Health Organization Global Foodborne Infections Network Country Data Bank: results of quality assured laboratories from 2001 to 2007". Foodborne Pathogens and Disease. 8 (8): 887–900. doi:10.1089/fpd.2010.0787. PMID 21492021.
  6. Goldrick, Barbara (March 2003). "Emerging Infections: Foodborne Diseases". The American Journal of Nursing. 103 (3): 105–106. doi:10.1097/00000446-200303000-00043. JSTOR 29745004. PMID 12635640.
  7. Elward A, Grim A, Schroeder P, Kieffer P, Sellenriek P, Ferrett R, Adams HC, Phillips V, Bartow R, Mays D, Lawrence S, Seed P, Holzmann-Pazgal G, Polish L, Leet T, Fraser V (June 2006). "Outbreak of Salmonella javiana infection at a children's hospital". Infection Control and Hospital Epidemiology. 27 (6): 586–92. doi:10.1086/506483. JSTOR 10.1086/506483. PMID 16755478.
  8. "Typhoid Outbreak in Pakistan Linked to Extensively Drug-Resistant Bacteria". The Scientist Magazine®. Retrieved 2018-09-03.
  9. Klemm, Elizabeth J.; Shakoor, Sadia; Page, Andrew J.; Qamar, Farah Naz; Judge, Kim; Saeed, Dania K.; Wong, Vanessa K.; Dallman, Timothy J.; Nair, Satheesh (2018-02-20). "Emergence of an Extensively Drug-Resistant Salmonella enterica Serovar Typhi Clone Harboring a Promiscuous Plasmid Encoding Resistance to Fluoroquinolones and Third-Generation Cephalosporins". mBio. 9 (1). doi:10.1128/mBio.00105-18. ISSN 2150-7511. PMC 5821095. PMID 29463654.
  10. "Extensively Drug-Resistant Typhoid Fever in Pakistan - Alert - Level 2, Practice Enhanced Precautions - Travel Health Notices | Travelers' Health | CDC". wwwnc.cdc.gov. Retrieved 2018-09-03.
  11. Nuccio SP, Bäumler AJ (March 2014). "Comparative analysis of Salmonella genomes identifies a metabolic network for escalating growth in the inflamed gut". mBio. 5 (2): e00929–14. doi:10.1128/mBio.00929-14. PMC 3967523. PMID 24643865.
  12. "Salmonella nomenclature". March 19, 2005. Archived from the original on 2006-04-15.
  13. "Scientific Nomenclature". Emerging Infectious Dieases. Centers for Disease Control and Prevention. Retrieved 17 February 2020.
  14. "Salmonella spp. comparative sequencing". Archived from the original on 2007-11-14.
  15. Feasey NA, Dougan G, Kingsley RA, Heyderman RS, Gordon MA (June 2012). "Invasive non-typhoidal salmonella disease: an emerging and neglected tropical disease in Africa". Lancet. 379 (9835): 2489–99. doi:10.1016/s0140-6736(11)61752-2. PMC 3402672. PMID 22587967.
  16. Hammarlöf DL, Kröger C, Owen SV, Canals R, Lacharme-Lora L, Wenner N, Schager AE, Wells TJ, Henderson IR, Wigley P, Hokamp K, Feasey NA, Gordon MA, Hinton JC (March 2018). "Salmonella". Proceedings of the National Academy of Sciences of the United States of America. 115 (11): E2614–E2623. doi:10.1073/pnas.1714718115. PMC 5856525. PMID 29487214.
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