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.

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 hamsters 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).

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.

''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 process in the evolution of host adaptation. Additional reconstructed genomes from colonial Mexico suggest ''S. enterica'' as the cause of ''cocoliztli'', an epidemic in 16th-century New Spain.

Pathogenesis

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.

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.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 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 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 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.

Nomenclature

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

* 1984 Rajneeshee bioterror attack
* AsrC small RNA
* Bacterial small RNA
* HilD 3'UTR
* IsrM small RNA
* PinT small RNA
* Typhoid Mary

References

External links

Notes on ''Salmonella'' nomenclature
*

Current research on ''Salmonella typhimurium '' at the Norwich Research Park
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Type strain of ''Salmonella enterica'' at Bac''Dive'' - the Bacterial Diversity Metadatabase

{{Taxonbar, from=Q2264864

Salmonella
Gram-negative bacteria
Typhoid fever