Salmonella Typhimurium
| Salmonella Typhimurium | ||||||||||||
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Colonies of Salmonella Typhimurium on Hectoen enteric agar |
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| S. enterica subsp. enterica ser. Typhimurium | ||||||||||||
| (ex Kauffmann and Edwards 1952) Le Minor and Popoff 1987 |
Salmonella Typhimurium (actually: Salmonella enterica subsp. Enterica ser. Typhimurium or Salmonella enterica subsp. I ser. Typhimurium ) is one of the serovars of the species Salmonella enterica . It is a flagellated and therefore motile, gram-negative bacterium and, like all serovars of subspecies I, contains the O-antigen , which is part of the lipopolysaccharide complex of the bacterial cell wall. Salmonella Typhimurium is one of the main causing bacteria of human gastroenteritis . In contrast to its close relative, Salmonella Typhi, Salmonella Typhimurium affectsnot only humans but also many other mammals ( Latin : typhi murium = typhoid fever in mice).
Occurrence
Salmonella Typhimurium has been found in the US, UK, Canada, Germany, France, Austria and Denmark and is one of the two most frequently detected serovars in human infections in Germany. The bacterium has a lower risk status for the population than Salmonella Typhi, but more people die from non-typhoid salmonellosis , which is caused by Salmonella Typhimurium. Small children and the elderly are particularly affected. Salmonella Typhimurium can multiply in the temperature range of 5–45 ° C. Salmonella are resistant to oxidative stress , so they can avoid phagocytosis . Temperatures above 70 ° C and common disinfectants kill Salmonella very quickly.
Structure and genome
LT2 is the strain of Salmonella Typhimurium, which is mainly used for molecular biological and cellular studies. They have a greatly weakened virulence.
The genome of Salmonella Typhimurium strain LT2 is essentially divided into two components: the chromosome and the plasmid pSLT. The chromosome (size: 4,857,432 bp ) has a total of 4,489 coding sequences , including 39 pseudogenes . In addition, it contains 85 tRNA , seven tRNA clusters, 11 structural RNA and one tRNA pseudogene. The pseudogenes are responsible for maltose regulation and trehalose metabolism. 11 operons (stc, bcf, fim, lpf, saf, stb, std, stf, sth, sti and stj) are located on the chromosome . They encode fimbriae on the cell surface, which make contact with the intestinal epithelium.
Antibiotic resistance genes to ampicillin, streptomycin, chloramphenicol, sulfonamides and tetracyclines as well as resistances to trimethoprim and ciprofloxacin are encoded in the chromosome.
The GC content is 53% in the chromosome and in the plasmid.
In contrast, the plasmid pSLT (size 93,939bp) contains only one structural RNA and 108 coding sequences, including six pseudogenes. The plasmid also has an operon (pef) for the formation of fimbriae. Salmonella Typhimurium contains four prophages (Gifsy-1, Gifsy-2, Fels-1 and Fels-2) that play a role in the infections.
discovery
Salmonella Typhimurium strain LT2 was isolated in the 1940's and used in phage-transferring transduction studies . Attenuated bacteria of the genus were given as an oral vaccine to reveal antigens from other pathogens and to transport proteins to tumors.
The sequencing of the Salmonella Typhimurium LT2 genome took place in 2001 as part of an experiment. Two methods of sequencing were used: whole genome shotgun sampling and sampling of gel-purified restriction fragments.
First, the homology of Salmonella Typhimurium to other intestinal bacteria was determined by comparing it with the complete genomes of three related bacterial strains ( Escherichia coli K12 and O157: H7 and S. typhi ). They were hybridized on a microarray on which genes from Salmonella Typhimurium LT2 were applied.
Homology
Comparisons with the four bacterial genomes mentioned above showed that they are collinear in a high percentage. However, they showed large differences in the inverse replication terms .
At least 55% of all pseudogenes of Salmonella Typhimurium are homologous to the genomes of some enterobacteria ( Salmonella Typhi, Salmonella Paratyphi A and B, S. enterica subsp. Arizonae , S. bongori , E. coli K12 and O157: H7 and K. pneumoniae ), which corresponds to 2.5 Mb of the Salmonella Typhimurium LT2 genome. Of the 108 coding sequences and pseudogenes in the plasmid of Salmonella Typhimurium LT2, only three were homologous to the enterobacteria Salmonella Typhi and Salmonella Paratyphi A.
Lateral gene transfer was common: 11% of the S. typhi genes and 29% of the E. coli K12 genes migrated into the Salmonella Typhimurium LT2 genome. The prophages Gifsy-1 and -2, Fels-1 and -2 occurred only in Salmonella Typhimurium and are not present in the other eight enterobacteria despite homology.
At least one of the coding sequences in Salmonella Typhimurium is similar to one in the enterobacteria Salmonella Typhi, Salmonella Paratyphi A / B. There are also 121 coding sequences that are not found in any of the other enterobacteria.
Clinical picture
The infection with Salmonella Typhimurium occurs through contaminated food, which means both the consumption of infected food (e.g. infected fruit or contaminated peanut butter) and the consumption of products that come from infected animals (e.g. meat products). Well cooked meat minimizes the risk of infection, as all salmonella are sensitive to heat.
Salmonella Typhimurium can be transmitted through the faeces of sick animals or humans. Hygiene plays a major role in this context. Inadequate hand washing after removing pet droppings, using the toilet or feeding a sick pet increases the risk of infection.
The intestinal bacteria can penetrate the stomach's barrier because the pH value of the stomach depends on the food ingested and the stomach acid is so variable for bacteria. Salmonella Typhimurium penetrates the epithelial cells of the small intestine and is transported to the underlying connective tissue, where it multiplies. Symptoms are diarrhea, fever, and abdominal pain that start 12–72 hours after infection and last for a week.
Diagnosis
Salmonella Typhimurium can usually be cultured from stool samples without difficulty. The stool sample is normally pre-incubated overnight in an enrichment liquid (e.g. selenite broth) and then spread onto a selective differentiation medium (e.g. XLD agar ). Suspicious colonies are then inoculated the next day onto a Kligler agar slant, from which the serological differentiation is partly carried out.
On the Kligler agar, Salmonella Typhimurium (like other enteritic Salmonella) shows the following properties: oblique layer red (lactose negative, therefore also colorless on MacConkey agar ), upper layer yellow (glucose positive), H 2 S positive (black precipitate in the upper layer which can completely cover the yellow color), gas formation visible. If a complete biochemical or mass spectrometric differentiation is not carried out, the positive catalase and the negative urease reaction should also be detected in order to reliably exclude any confusion with bacteria of the genera Citrobacter and Proteus . The positive lysine decarboxylase and the negative phenylalanine deaminase as key biochemical reactions can also help here.
In the serological differentiation that is always required, Salmonella Typhimurium shows the following central properties: Agglutination with NaCl solution negative, positive with polyvalent Salmonella antiserum ("Omni" serum), positive with O: 4 serum (this shows that it belongs to group O: 4 or group B according to the old nomenclature, see also Kauffmann-White scheme ), positive with serum i of the first H phase and positive with serum 1 and 2 of the second H phase (the latter agglutination reaction is partially suppressed first H phase using a special agar ("swarm agar") necessary).
Vaccinations
Even today, Salmonella Typhimurium is often used in a weakened version in laboratory work, as it causes the same fever symptoms in mice as in humans.
A Typhimurium live vaccine has been available since 2002, which is sold under the name “SALMOPORC” and injected into suckling pigs.
literature
- Michael McClelland, Kenneth E. Sanderson, John Spieth, Sandra W. Clifton, Phil Latreille, Laura Courtney, Steffen Porwollik, Johar Ali, Mike Dante, Feiyu Du, Shunfang Hou, Dan Layman, Shawn Leonard, Christine Nguyen, Kelsi Scott, Andrea Holmes, Neenu Grewal, Elizabeth Mulvaney, Ellen Ryan, Hui Sun, Liliana Florea, Webb Miller, Tamberlyn Stoneking, Michael Nhan, Robert Waterston, Richard K. Wilson: Complete genome sequence of Salmonella enterica serovar Typhimurium LT2 . In: Nature . tape 413 , no. 6858 , September 2001, p. 852-856 , doi : 10.1038 / 35101614 .
Individual evidence
- ↑ Pascal Le Gros Bin Beck Songhet: Salmonella Typhimurium diarrhea as a result of pathogen invasion and immune defense . Zurich 2010, doi : 10.3929 / ethz-a-006323804 (dissertation, ETH Zurich).
- ↑ a b Salmonella Typhimurium DT104 Situation Assessment (PDF; 103 kB), December 1997.
- ↑ Salmonellosis (salmonella gastroenteritis). RKI guide for doctors. Robert Koch Institute , August 16, 2011, accessed on February 19, 2013 .
- ↑ innovations-report.com: Salmonella bacteria sequenced .
- ↑ TA Halsey, A. Vazquez-Torres, DJ Gravdahl, FC Fang, SJ Libby: The ferritin-like Dps protein is required for Salmonella enterica serovar Typhimurium oxidative stress resistance and virulence. In: Infection and Immunity . Volume 72, Number 2, February 2004, pp. 1155-1158. PMID 14742565 . PMC 321587 (free full text).
- ↑ Statement of the ZKBS : Salmonella Typhimurium LT2 aroA, galE or cya, crp (1996)
- ↑ Nature: Complete genome sequence of: Salmonella enterica: serovar Typhimurium LT2
- ↑ CDC: Salmonella Typhimurium Infections Linked to Peanut Butter , April 29, 2009.
- ↑ BfR: New studies show: Salmonella is also a problem in fattening pigs and fattening turkeys
- ↑ CDC: Q and A Related to the Salmonella Typhimurium Outbreak and Pets
- ↑ Bacteria Genomes - SALMONELLA TYPHIMURIUM ( Memento from July 1, 2012 in the Internet Archive )
- ↑ Federal Office for Consumer Protection and Food Safety: Statement by the ZKBS on the classification of Salmonella Typhimurium LT2 strains and Salmonella Typhimurium strains with stable mutations in the genes aroA, galE or cya and crp as recipient organisms in genetic engineering work , January 1996.
- ↑ Matthias Eddicks: Examination of the tolerance of the Salmonella Typhimurium live vaccine Salmoporc® when administered orally to three-day-old suckling pigs, taking into account the excretion, persistence and immunogenicity of the vaccine strain. (PDF; 461 kB) Dissertation, LMU Munich: Veterinary Faculty 2006. urn : nbn: de: bvb: 19-63308
- ↑ Helmut Tschäpe, Rolf Reissbrodt and Rita Prager: Salmonella spp. In: Birgid Neumeister, Heinrich K. Geiss, Rüdiger W. Braun and Peter Kimmig (eds.): Microbiological diagnostics . 2nd Edition. Georg Thieme Verlag, Stuttgart - New York 2009, ISBN 978-3-13-743602-7 , pp. 450-454 .
- ^ Patrick AD Grimont and François-Xavier Weill: Antigenic Formulas of the Salmonella Serovars. (No longer available online.) WHO Collaboration Center for Reference and Research on Salmonella , 2007, p. 19 , archived from the original on July 1, 2013 ; accessed on February 20, 2013 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ innovations-report.com: Salmonella bacteria sequenced
