Salmonella

Salmonella
Scientific classification
Kingdom: Bacteria
Class: Gamma Proteobacteria
Order: Enterobacteriales
Family: Enterobacteriaceae
Genus: Salmonella
Lignieres 1900
Species

S. bongori
S. enterica

Salmonella is a genus of rod-shaped, Gram-negative, non-spore forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which project in all directions (i.e. peritrichous). They are chemoorganotrophs, obtaining their energy from oxidation and reduction reactions using organic sources, and are facultative anaerobes. Most species produce hydrogen sulfide,[1] which can readily be detected by growing them on media containing ferrous sulfate, such as TSI. Most isolates exist in two phases: a motile phase I and a nonmotile phase II. Cultures that are nonmotile upon primary culture may be switched to the motile phase using a Cragie tube.

Salmonella is closely related to the Escherichia genus and are found worldwide in cold- and warm-blooded animals (including humans), and in the environment. They cause illnesses like typhoid fever, paratyphoid fever, and the foodborne illness.[2]

Salmonella is typically pronounced /ˌsælməˈnɛlə/ voicing the initial letter "L," since it is named for pathologist Daniel Elmer Salmon. Infection from the salmon fish is infrequent when compared to infections from other animals.

Contents

Salmonella as disease-causing agents

Salmonella infections are zoonotic and can be transferred between humans and nonhuman animals. Many infections are due to ingestion of contaminated food. A distinction is made between enteritis Salmonella and typhoid/paratyphoid Salmonella, where the latter — because of a special virulence factor and a capsule protein (virulence antigen) — can cause serious illness, such as Salmonella enterica subsp. enterica serovar Typhi, or Salmonella typhi). Salmonella typhi. is adapted to humans and does not occur in animals.

Enteritis Salmonella or Food Poisoning Salmonella

Constitutes a group consisting of potentially all other serotypes (over a thousand) of the Salmonella bacterium, most of which have never been found in humans. These are encountered in various Salmonella species, most having never been linked to a specific host, and can also infect humans. It is therefore a zoonotic disease. The organism enters through the digestive tract and must be ingested in large numbers to cause disease in healthy adults. Gastric acidity is responsible for the destruction of the majority of ingested bacteria. The infection usually occurs as a result of massive ingestion of foods in which the bacteria are highly concentrated similarly to a culture medium. However, infants and young children are much more susceptible to infection, easily achieved by ingesting a small number of bacteria. It has been shown that, in infants, the contamination could be through inhalation of bacteria-laden dust. After a short incubation period of a few hours to one day, the germ multiplies in the intestinal lumen causing an intestinal inflammation with diarrhea that is often muco-purulent and bloody. In infants, dehydration can cause a state of severe toxicosis. The symptoms are usually mild. There is normally no sepsis, but it can occur exceptionally as a complication in weakened elderly patients (Hodgkin's disease, eg.). Extraintestinal localizations are possible, especially Salmonella meningitis in children, osteitis, etc. Enteritis Salmonella (e.g., Salmonella enterica subsp. enterica serovar enteritidis) can cause diarrhea, which usually does not require antibiotic treatment. However, in people at risk such as infants, small children, the elderly, Salmonella infections can become very serious, leading to complications. If these are not treated, HIV patients and those with suppressed immunity can become seriously ill. Children with sickle cell anemia who are infected with Salmonella may develop osteomyelitis.

In Germany, Salmonella infections must be reported .[3] Between 1990 and 2005, the number of officially recorded cases decreased from approximately 200,000 cases to approximately 50,000. It is estimated that every fifth person in Germany is a carrier of Salmonella. In the USA, there are approximately 40,000 cases of Salmonella infection reported each year.[4] According to the World Health Organization, over 16 million people worldwide are infected with typhoid fever each year, with 500,000 to 600,000 fatal cases.

Salmonella can survive for weeks outside a living body. They have been found in dried excrement after over 2.5 years. Salmonella are not destroyed by freezing .[5][6]Ultraviolet radiation and heat accelerate their demise; they perish after being heated to 55 °C (131 °F) for one hour, or to 60 °C (140 °F) for half an hour. To protect against Salmonella infection, it is recommended that food be heated for at least ten minutes at 75 °C (167 °F) so that the center of the food reaches this temperature.

The AvrA toxin injected by the type three secretion system of Salmonella typhimurium works to inhibit the innate immune system by virtue of its serine/threonine acetyltransferase activity and requires binding to eukaryotic target cell phytic acid (IP6).[7] This leaves the host more susceptible to infection.

History

The genus Salmonella was named after Daniel Elmer Salmon, an American veterinary pathologist. While Theobald Smith was the actual discoverer of the type bacterium (Salmonella enterica var. choleraesuis) in 1885, Dr. Salmon was the administrator of the USDA research program, and thus the organism was named after him.[8] Smith and Salmon had been searching for the cause of common hog cholera and proposed this organism as the causal agent. Later research, however, would show that this organism (now known as Salmonella enterica) rarely causes enteric symptoms in pigs,[9] and was thus not the agent they were seeking (which was eventually shown to be a virus). However, related bacteria in the genus Salmonella were eventually shown to cause other important infectious diseases.

Salmonella nomenclature

Salmonella nomenclature is complicated. Initially each Salmonella species was named according to clinical considerations,[10] e.g., Salmonella typhi-murium (mouse typhoid fever), S. cholerae-suis (hog cholera). After it was recognized that host specificity did not exist for many species, new strains (or serovar, short for serological variants) received species names according to the location at which the new strain was isolated. Later, molecular findings led to the hypothesis that Salmonella consisted of only one species,[11] S. enterica, and the serovar were classified into six groups,[12] two of which are medically relevant. But as this now formalized nomenclature[13][14] is not in harmony with the traditional usage familiar to specialists in microbiology and infectologists, the traditional nomenclature is common. Currently, there are two recognized species: S. enterica and S. bongori, with six main subspecies: enterica (I), salamae (II), arizonae (IIIa), diarizonae (IIIb), houtenae (IV), and indica (VI).[15] Historically, serotype (V) was bongori, which is now considered its own species. The serovar classification of Salmonella is based on the Kauffman-White classification scheme that permits serological varieties to be differentiated from each other. Newer methods for Salmonella typing and subtyping include genome-based methods such as pulsed field gel electrophoresis (PFGE), Multiple Loci VNTR Analysis (MLVA), Multilocus sequence typing (MLST) and (multiplex-) PCR-based methods.[16]

Genetics

Serovar Typhimurium has considerable diversity and may be very old. The majority of the isolates belong to a single clonal complex. Isolates are divided into phage types, but some phage types do not have a single origin as determined using mutational changes. Phage type DT104 is heterogeneous and represented in multiple sequence types, with its multidrug-resistant variant being the most successful and causing epidemics in many parts of the world.

Serovar Typhi is relatively young compared to Typhimurium, and probably originated approximately 30,000-50,000 years ago.

Sources of infection

Salmonella bacteria can survive several weeks in a dry environment and several months in water; thus, they are frequently found in polluted water, contamination from the excrement of carrier animals being particularly important. Aquatic vertebrates, notably birds and reptiles, are important vectors of salmonella. Poultry, cattle, and sheep frequently being agents of contamination, salmonella can be found in food, particularly meats and eggs.

Deaths

About 142,000 Americans are infected each year with Salmonella enteritidis from chicken eggs, and about 30 die.[18] The shell of the egg may be contaminated with salmonella by feces or environment, or its interior (yolk) may be contaminated by penetration of the bacteria through the porous shell or from a hen whose infected ovaries contaminate the egg during egg formation. [19][20] Nevertheless, such interior egg yolk contamination is theoretically unlikely.[21] [22] [23] [24] Even under natural conditions, the rate of infection was found to be very small (0.6% in a study of naturally-contaminated eggs[25] and 3.0% among artificially- and heavily-infected hens[26]).

Medically relevant representatives

See also

References

  1. ↑ Clark MA, Barret EL (June 1987). "The phs gene and hydrogen sulfide production by Salmonella typhimurium.". J Bacteriology 169 (6): 2391–2397. http://jb.asm.org/cgi/content/short/169/6/2391. 
  2. ↑ Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. pp. 362–8. ISBN 0-8385-8529-9. 
  3. ↑ § 6 and § 7 of the German law on infectious disease prevention, Infektionsschutzgesetz
  4. ↑ Centers for Disease Control and Prevention
  5. ↑ Sorrells, K.M.; M. L. Speck and J. A. Warren (January 1970). "Pathogenicity of Salmonella gallinarum After Metabolic Injury by Freezing". Applied and Environmental Microbiology 19 (1): 39–43. PMID 5461164. http://aem.asm.org/cgi/content/abstract/19/1/39. Retrieved 2010-08-19. "Mortality differences between wholly uninjured and predominantly injured populations were small and consistent (5% level) with a hypothesis of no difference.". 
  6. ↑ Beuchat, L. R.; E. K. Heaton (June 1975). "Salmonella Survival on Pecans as Influenced by Processing and Storage Conditions". Applied and Environmental Microbiology 29 (6): 795–801. PMID 1098573. http://aem.asm.org/cgi/content/abstract/29/6/795. Retrieved 2010-08-19. "Little decrease in viable population of the three species was noted on inoculated pecan halves stored at -18, -7, and 5 C for 32 weeks.". 
  7. ↑ Mittal R, Peak-Chew SY, Sade RS, Vallis Y, McMahon HT (2010). "The acetyltransferase activity of the bacterial toxin YopJ of Yersinia is activated by eukaryotic host cell inositol hexakisphosphate". J Biol Chem 285 (26): 19927–34. doi:10.1074/jbc.M110.126581. PMID 20430892. PMC 2888404. http://www.jbc.org/content/early/2010/04/29/jbc.M110.126581.long. 
  8. ↑ "FDA/CFSAN - Food Safety A to Z Reference Guide - Salmonella". FDA - Center for Food Safety and Applied Nutrition. 2008-07-03. http://www.cfsan.fda.gov/~dms/a2z-s.html. Retrieved 2009-02-14. 
  9. ↑ http://www.cgmh.org.tw/chldhos/intr/c4a00/academy/bugs/salchole.html S. cholerasuis pathology. Accessed April 3., 2009
  10. ↑ F. Kauffmann: Die Bakteriologie der Salmonella-Gruppe. Munksgaard, Kopenhagen, 1941
  11. ↑ L. Le Minor, M. Y. Popoff: Request for an Opinion. Designation of Salmonella enterica. sp. nov., nom. rev., as the type and only species of the genus Salmonella. In: Int. J. Syst. Bacteriol., Bd. 37, 1987, S. 465–468
  12. ↑ M. W. Reeves, G. M. Evins, A. A. Heiba, B. D. Plikaytis, J. J. Farmer III: Clonal nature of Salmonella typhi and its genetic relatedness to other salmonellae as shown by multilocus enzyme electrophoresis and proposal of Salmonella bongori comb. nov. In: J. Clin. Microbiol. Bd. 27, 1989, S. 313–320. PMID 2915026
  13. ↑ Judicial Commission of the International Committee on Systematics of Prokaryotes: The type species of the genus Salmonella Lignieres 1900 is Salmonella enterica (ex Kauffmann and Edwards 1952) Le Minor and Popoff 1987, with the type strain LT2T, and conservation of the epithet enterica in Salmonella enterica over all earlier epithets that may be applied to this species. Opinion 80. In: Int. J. Syst. Evol. Microbiol. Bd. 55, 2005, S. 519–520. PMID 15653929
  14. ↑ B. J. Tindall, P. A. Grimont, G. M. Garrity, J. P. Euzeby: Nomenclature and taxonomy of the genus Salmonella . In: Int. J. Syst. Evol. Microbiol. Bd. 55, 2005, S. 521–524. PMID 15653930
  15. ↑ Janda JM, Abbott SL (2006). "The Enterobacteria", ASM Press.
  16. ↑ Porwollik, S (editor) (2011). Salmonella: From Genome to Function. Caister Academic Press. ISBN 978-1-904455-73-8. 
  17. ↑ "Ongoing investigation into reptile associated salmonella infections". Health Protection Report 3 (14). 9 April 2009. http://www.hpa.org.uk/hpr/archives/2009/news1409.htm#reptiles. Retrieved 12 April 2009. 
  18. ↑ "Administration Urged to Boost Food Safety Efforts". Washington Post. 2009. http://www.washingtonpost.com/wp-dyn/content/article/2009/07/07/AR2009070702343.html?hpid=topnews. Retrieved 2009-07-07. "Among them is a final rule, issued by the FDA, to reduce the contamination in eggs. About 142,000 Americans are infected each year with Salmonella enteritidis from eggs, the result of an infected hen passing along the bacterium. About 30 die." 
  19. ↑ Gantois, Inne; Richard Ducatelle, Frank Pasmans, Freddy Haesebrouck, Richard Gast, Tom J. Humphrey, Filip Van Immerseel (July 2009). "Mechanisms of egg contamination by Salmonella Enteritidis". FEMS Microbiology Reviews 33 (4): 718–738. doi: 10.1111/j.1574-6976.2008.00161.x. http://onlinelibrary.wiley.com/doi/10.1111/j.1574-6976.2008.00161.x/abstract. Retrieved 2010-08-19. "Eggs can be contaminated on the outer shell surface and internally. Internal contamination can be the result of penetration through the eggshell or by direct contamination of egg contents before oviposition, originating from infection of the reproductive organs. Once inside the egg, the bacteria need to cope with antimicrobial factors in the albumen and vitelline membrane before migration to the yolk can occur". 
  20. ↑ Humphrey, T. J. (January 1994). "Contamination of egg shell and contents with Salmonella enteritidis: a review". International Journal of Food Microbiology 21 (1-2): 31–40. doi: 10.1016/0168-1605(94)90197-X. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T7K-476W8CY-KY&_user=10&_coverDate=01%2F31%2F1994&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1436086824&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=7115aebaca62d2313655fffe0ab413b5. Retrieved 2010-08-19. "Salmonella enteritidis can contaminate the contents of clean, intact shell eggs as a result of infections of the reproductive tissue of laying hens. The principal site of infection would appear to be the upper oviduct. In egg contents the most important sites of contamination are either the outside of the vitelline membrane or the albumen surrounding it. In fresh eggs, only few salmonellaa are present and as albumen is an iron-restricted environment, growth will only occur once storage-related changes to vitelline membrane permeability, which allow salmonellas to invade yolk contents, have taken place.". 
  21. ↑ Stokes, J.L.; W.W. Osborne, H.G. Bayne (1956 September). "Penetration and Growth of Salmonella in Shell Eggs". Journal of Food Science 21 (5): 510–518. doi: 10.1111/j.1365-2621.1956.tb16950.x. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.1956.tb16950.x/abstract. Retrieved 2010-08-19. "Normally, the oviduct of the hen is sterile and therefore the shell and internal contents of the egg are also free of microorganisms (10,16). In some instances, however, the ovaries and oviduct may be infected with Salmonella and these may be deposited inside the egg (12). More frequently, however, the egg becomes contaminated after it is laid.". 
  22. ↑ Okamura, Masashi; Yuka Kamijima, Tadashi Miyamoto, Hiroyuki Tani, Kazumi Sasai, Eiichiroh Baba (2001). "Differences Among Six Salmonella Serovars in Abilities to Colonize Reproductive Organs and to Contaminate Egges in Laying Hens". Avian Diseases 45: 61–69. PMID 11332500. http://www.jstor.org/pss/1593012. Retrieved 2010-08-19. "when hens were artificially infected to test for transmission rate to yolks: "Mature laying hens were inoculated intravenously with 106 colony-forming units of Salmonella enteritidis, Salmonella typhimurium, Salmonella infantis, Salmonella hadar, Salmonella heidelberg, or Salmonella montevideo to cause the systemic infection. Salmonella enteritidis was recovered from three yolks of the laid eggs (7.0%), suggesting egg contamination from the transovarian transmission of S. enteritidis."". 
  23. ↑ Gast, RK; D.R. Jones, K.E. Anderson, R. Guraya, J. Guard, P.S. Holt (August 2010). "In vitro penetration of Salmonella Enteritidis through yolk membranes of eggs from 6 genetically distinct commercial lines of laying hens". Poultry Science 89 (8): 1732–1736. PMID 20634530 doi: 10.3382/ps.2009-00440 . http://ps.fass.org/cgi/content/abstract/89/8/1732. Retrieved 2010-08-20. "In this study, egg yolks were infected at the surface of the yolk (vitelline membrane) to determine the percentage of yolk contamination (a measure used to determine egg contamination resistance, with numbers lower than 95% indicating increasing resistance): --Overall, the frequency of penetration of Salmonella Enteritidis into the yolk contents of eggs from individual lines of hens ranged from 30 to 58% and the mean concentration of Salmonella Enteritidis in yolk contents after incubation ranged from 0.8 to 2.0 log10 cfu/mL.--". 
  24. ↑ Jaeger, Gerald (Jul-Aug 2009). "Contamination of eggs of laying hens with S. Enteritidis". Veterinary Survey (Tierärztliche Umschau) 64 (7-8): 344–348. http://www.scopus.com/record/display.url?eid=2-s2.0-70249089685&origin=AuthorNamesList&txGid=zUlZlrGCjw9FgQXhSMPv1sc%3a3. Retrieved 2010-08-20. "The migration of the bacterium into the nutritionally rich yolk is constrained by the lysozyme loaded vitelline membrane, and would need warm enough storage conditions within days and weeks. The high concentration on of antibodies of the yolk does not inhibit the Salmonella multiplication. The transovarian contamination of the developing eggs with S. Enteritidis will result in the occurrence of this bacterium in the laid eggs relatively seldom only, because of the bactericidal efficacy of the antimicrobial peptides". 
  25. ↑ Humphrey, T.J.; A. Whitehead, A. H. L. Gawler, A. Henley and B. Rowe (1991). "Numbers of Salmonella enteritidis in the contents of naturally contaminated hens' eggs". Epidemiology and Infection 106: 489–496. doi: 10.1017/S0950268800067546. http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=5853708. Retrieved 2010-08-19. "Over 5700 hens eggs from 15 flocks naturally infected with Salmonella enteritidis were examined individually for the presence of the organism in either egg contents or on shells. Thirty-two eggs (0·6%) were positive in the contents. In the majority, levels of contamination were low.". 
  26. ↑ Gast, Richard; Rupa Guraya, Jean Guard, Peter Holt, Randle Moore (March 2007). "Colonization of specific regions of the reproductive tract and deposition at different locations inside eggs laid by hens infected with Salmonella Enteritidis or Salmonella Heidelberg". Journal of Avian Diseases 51 (1): 40–44. PMID 17461265. http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=196876. Retrieved 2010-08-20. "when hens are artificially infected with unrealistically large doses (according to the author): --In the present study, groups of laying hens were experimentally infected with large oral doses of Salmonella Heidelberg, Salmonella Enteritidis phage type 13a, or Salmonella Enteritidis phage type 14b. For all of these isolates, the overall frequency of ovarian colonization (34.0%) was significantly higher than the frequency of recovery from either the upper (22.9%) or lower (18.1%) regions of the oviduct. No significant differences were observed between the frequencies of Salmonella isolation from egg yolk and albumen (4.0% and 3.3%, respectively)--". 

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