Salmonella enterica subsp. enterica

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Salmonella enterica subsp. enterica
Salmonella enterica serovar typhimurium 01.jpg
Salmonella Typhimurium colonies on a Hektoen enteric agar plate
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Domain: Bacteria
Phylum: Pseudomonadota
Class: Gammaproteobacteria
Order: Enterobacterales
Family: Enterobacteriaceae
Genus: Salmonella
Species:
S. enterica
Subspecies:
S. e. subsp. enterica
Trinomial name
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]

Contents

Serovars

Salmonella enterica subsp. enterica serovars are defined based on their somatic (O) and flagellar (H) antigens, with over 2,600 serovars in total; only about 50 of these serovars are common causes of infections in humans. [2] Most of these serovars are found in the environment and survive in plants, water, and soil; many serovars have broad host ranges that allow them to colonize different species in mammals, birds, reptiles, amphibians, and insects. Zoonotic diseases, like Salmonella, spread between the environment and people. [3]

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. [4] 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. [5]

The CDC publishes a Salmonella Annual Report with a list of serovars most commonly associated with human illness, the top 10 serovars are listed below: [6]

RankSerotypePercent
1Enteritidis16.8
2Newport10.1
3Typhimurium9.8
4Javiana5.8
5I 4,[5],12:i:-4.7
6Infantis2.7
7Muenchen2.6
8Montevideo2.2
9Braenderup2.1
10Thompson1.7
-Other41.5

Studies have concluded most strains of Salmonella enterica subsp. enterica serovars possess serotype-specific virulence plasmids. These are plasmid-associated virulence characterized by low-copy-number plasmids and depending on the serovar, its size ranges from 50 to 100 kb. [7] In 2012, CDC's PulseNet became aware of a emergent multi-drug resistant Serovar Infantis SNP cluster, named REPJFX01. This SNP cluster has a large megaplasmid (pESI) that contains multiple drug-resistance genes. [8] The USDA NARMS stated that because of this pESI-plasmid, serovar Infantis is the leading serovar in poultry. [9] NCBI has over 12,500 isolates in the REPJFX01 SNP cluster, with over 3,700 being clinical isolates. [10] Serovar Enteritidis, which is the most common serovar isolated in human clinical cases, has also been found to produce endotoxins, coded by the stn and slyA genes, that attribute to the pathogenicity of Enteritidis. [11]

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. [12] Multidrug resistant strains have been present since the late 1970s in Africa and Asia. [13] 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. [14]

Nomenclature

The nomenclature of Salmonella enterica has long been a topic of debate in the microbiology community. [15] Originally in the 1880s, Salmonella species were named after the disease, host, or geological location they were associated with; however, this taxonomic characterization was contested due to genus members being categorized incompatibly with their genetic similarities. In the 1980s, the emergence of nucleotide sequencing and DNA hybridization led many established bacteriologists such as Le Minor and Popoff (1987), Euzéby (1999), and Ezaki and Yabuuchi (2000) to put forth their proposals for nomenclature changes. [16] It was not until 2005, that Le Minor and Popoff reproposed and established that "Salmonella enterica" would be the approved species name – excluding Salmonella bongori – and that Salmonella enterica contains six subspecies, of which Salmonella enterica subsp. enterica contains the most serovars. [17] Technological advancements allow researchers to use whole genome sequencing data to identify and group serovars using two methods: sequence typing and antigen recognition. [18]

Serovar names are capitalized but not italicized or underlined. Serovars may be designated in full form or short form (includes just the genus and serovar names). For example, in full designation Salmonella enterica subsp. enterica serovar Typhi is written as such, but in short designation it is written as Salmonella Typhi. [19] Each serovar can have many strains, as well, which allows for a rapid increase in the total number of antigenically variable bacteria. [20]

Epidemiology

The World Health Organization characterizes salmonellosis as a foodborne disease whose symptoms include diarrhea, fever, nausea, vomiting, and in severe cases death. [21] Salmonellosis has been assessed to primarily occur in human hosts due to bacterial colonization of the intestinal tract after the consumption of contaminated food or water, but it is also known to spread from person-to-person via the fecal-oral route. [22] To reduce the risk associated with contracting this disease, proper food safety measures should be applied to high-risk food products including poultry, beef, pork, lamb, eggs, and fresh produce. [23] Food manufacturers, ingredient suppliers, restaurants, and home cooks should practice sanitary processing procedures, store foods below 5 °C, and thoroughly cook all foods to their designated safe-to-eat temperatures. [23] It has become increasingly difficult to mitigate the presence of salmonellosis infections across the human population due to the unique nature of multidrug-resistant serovars as a result of the counterproductive effects to use antibiotics as a broad spectrum treatment. [24] 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. [25] 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. [26]

Survival and stress

There are factors that can increase the infection risk. These include a higher pH in the stomach, gastric resection, and treatment with anti acid buffering. [27] If the stomach has a lower pH, then this helps as a defensive technique to potentially avoid infection. [28]

This strain is mesophilic and some can survive extremely low or high temperatures which can range from 2 °C – 54 °C. [29] Sigma factors inside the cell control the gene expression and they can sense the changes in the environment from the outer membrane by activation of genes that then respond to heat stress and adapt accordingly. [30] S. enterica also can quickly respond to cold temperatures by cold shock proteins (CSP) by synthesizing themselves so that the cell can later resume growth. [31] Chlorine can be a chemical stressor to S. enterica because once chlorine is present, S. enterica can produce a biofilm that provides itself with a exopolysaccharide matrix that has the ability of a chemical attack against chlorine. [32] From this, chlorine has preventative measures for biofilm formation in poultry drinking systems and this reduces the risk of S. enterica. [33] Successful adaptation allows S. enterica to withstand more acidic conditions, counteracting stomach antibacterial effects. [34]

Related Research Articles

<span class="mw-page-title-main">Typhoid fever</span> Disease caused by the bacteria Salmonella Typhi

Typhoid fever, also known simply as typhoid, is a disease caused by Salmonella enterica serotype Typhi bacteria, also called SalmonellaTyphi. 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 days. This is commonly accompanied by weakness, abdominal pain, constipation, headaches, and mild vomiting. Some people develop a skin rash with rose colored spots. In severe cases, people may experience confusion. Without treatment, symptoms may last weeks or months. Diarrhea may be severe, but is uncommon. Other people may carry it without being affected, but are still contagious. Typhoid fever is a type of enteric fever, along with paratyphoid fever. Salmonella enterica Typhi is believed to infect and replicate only within humans.

<i>Salmonella</i> Genus of prokaryotes

Salmonella is a genus of rod-shaped (bacillus) gram-negative bacteria of the family Enterobacteriaceae. The two known species of Salmonella are Salmonella enterica and Salmonella bongori. S. enterica is the type species and is further divided into six subspecies that include over 2,600 serotypes. Salmonella was named after Daniel Elmer Salmon (1850–1914), an American veterinary surgeon.

<i>Salmonella enterica</i> Species of bacterium

Salmonella enterica is a rod-shaped, flagellate, facultative anaerobic, Gram-negative bacterium and a species of the genus Salmonella. It is divided into six subspecies, arizonae (IIIa), diarizonae (IIIb), houtenae (IV), salamae (II), indica (VI), and enterica (I). A number of its serovars are serious human pathogens; many of them are serovars of Salmonella enterica subsp. enterica.

<span class="mw-page-title-main">Asymptomatic carrier</span> Organism which has become infected with a pathogen but displays no symptoms

An asymptomatic carrier is a person or other organism that has become infected with a pathogen, but shows no signs or symptoms.

<span class="mw-page-title-main">Salmonellosis</span> Infection caused by Salmonella bacteria

Salmonellosis is a symptomatic infection caused by bacteria of the Salmonella type. It is the most common disease to be known as food poisoning, these are defined as diseases, usually either infectious or toxic in nature, caused by agents that enter the body through the ingestion of food. In humans, the most common symptoms are diarrhea, fever, abdominal cramps, and vomiting. Symptoms typically occur between 12 hours and 36 hours after exposure, and last from two to seven days. Occasionally more significant disease can result in dehydration. The old, young, and others with a weakened immune system are more likely to develop severe disease. Specific types of Salmonella can result in typhoid fever or paratyphoid fever. Typhoid fever and paratyphoid fever are specific types of salmonellosis, known collectively as enteric fever, and are, respectively, caused by salmonella typhi & paratyphi bacteria, which are only found in humans. Most commonly, salmonellosis cases arise from salmonella bacteria from animals, and chicken is a major source for these infections.

<span class="mw-page-title-main">Serotype</span> Distinct variation within a species of bacteria or virus or among immune cells

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 epidemiologic classification of organisms to a level below the species. A group of serovars with common antigens is called a serogroup or sometimes serocomplex.

<i>Shigella flexneri</i> Species of bacterium

Shigella flexneri is a species of Gram-negative bacteria in the genus Shigella that can cause diarrhea in humans. Several different serogroups of Shigella are described; S. flexneri belongs to group B. S. flexneri infections can usually be treated with antibiotics, although some strains have become resistant. Less severe cases are not usually treated because they become more resistant in the future. Shigella are closely related to Escherichia coli, but can be differentiated from E.coli based on pathogenicity, physiology and serology.

<span class="mw-page-title-main">Paratyphoid fever</span> Bacterial infection caused by one of the three types of Salmonella enterica

Paratyphoid fever, also known simply as paratyphoid, is a bacterial infection caused by one of three types of Salmonella enterica. Symptoms usually begin 6–30 days after exposure and are the same as those of typhoid fever. Often, a gradual onset of a high fever occurs over several days. Weakness, loss of appetite, and headaches also commonly occur. Some people develop a skin rash with rose-colored spots. Without treatment, symptoms may last weeks or months. Other people may carry the bacteria without being affected; however, they are still able to spread the disease to others. Typhoid and paratyphoid are of similar severity. Paratyphoid and typhoid fever are types of enteric fever.

The Kauffmann–White classification or Kauffmann and White classification scheme is a system that classifies the genus Salmonella into serotypes, based on surface antigens. It is named after Philip Bruce White and Fritz Kauffmann. First the "O" antigen type is determined based on oligosaccharides associated with lipopolysaccharide. Then the "H" antigen is determined based on flagellar proteins. Since Salmonella typically exhibit phase variation between two motile phenotypes, different "H" antigens may be expressed. Salmonella that can express only one "H" antigen phase consequently have motile and non-motile phenotypes and are termed monophasic, whilst isolates that lack any "H" antigen expression are termed non-motile. Pathogenic strains of Salmonella Typhi, Salmonella Paratyphi C, and Salmonella Dublin carry the capsular "Vi" antigen, which is a special subtype of the capsule's K antigen.

<span class="mw-page-title-main">Leucine-responsive regulatory protein</span>

Leucine responsive protein, or Lrp, is a global regulator protein, meaning that it regulates the biosynthesis of leucine, as well as the other branched-chain amino acids, valine and isoleucine. In bacteria, it is encoded by the lrp gene.

The Vi capsular polysaccharide vaccine is a typhoid vaccine recommended by the World Health Organization for the prevention of typhoid. The vaccine was first licensed in the US in 1994 and is made from the purified Vi capsular polysaccharide from the Ty2 Salmonella Typhi strain; it is a subunit vaccine.

<span class="mw-page-title-main">Ty21a</span> Typhoid vaccine

Ty21a is a live attenuated bacterial vaccine that protects against typhoid. First licensed in Europe in 1983 and in the United States in 1989, it is an orally administered, live-attenuated Ty2 strain of S. Typhi in which multiple genes, including the genes responsible for the production of Vi, have been deleted so as to render it harmless but nevertheless immunogenic. It is one of the three typhoid vaccines currently recommended by the World Health Organization.

Andreas J. Bäumler is a professor in the Department of Medical Microbiology and Immunology at the University of California, Davis School of Medicine, in Davis, California. Bäumler studies the molecular mechanisms of Salmonella interaction with the intestinal mucosa. He is one of the leading researchers in the field of Salmonella research and has several highly cited publications on the topic of Salmonella infection, immunity to Salmonella, and the interactions between the host, the pathogen, and the intestinal microbiota during infection. Bäumler has a B.S. and a Ph.D. in Microbiology from University of Tübingen, Germany. Since 2010 Bäumler is a fellow of the American Academy of Microbiology and since 2020 of the Leopoldina. He is Editor in Chief of the scientific journal "Infection and Immunity." In 2021 he was awarded the Robert Koch Award for his pioneering work in understanding the regulation of the composition and function of our microflora by the cells of the intestinal epithelium.

Salmonella bongori is a pathogenic bacterium belonging to the genus Salmonella, and was earlier known as Salmonella subspecies V or S. enterica subsp. bongori or S. choleraesuis subsp. bongori. It is a Gram-negative, rod-shaped bacterium (bacillus), which causes a gastrointestinal disease called salmonellosis, characterized by cramping and diarrhoea. It is typically considered a microbe of cold-blooded animals, unlike other members of the genus, and is most frequently associated with reptiles.

<span class="mw-page-title-main">Gordon Dougan</span>

Gordon Dougan is a Professor in the Department of Medicine at the University of Cambridge and head of pathogen research and a member of the board of management at the Wellcome Sanger Institute in Cambridge, United Kingdom. He is also a Fellow of Wolfson College, Cambridge. During his career, Dougan has pioneered work on enteric diseases and been heavily involved in the movement to improve vaccine usage in developing countries. In this regard he was recently voted as one of the top ten most influential people in the vaccine world by people working in the area.

<span class="mw-page-title-main">Edward Thomas Ryan</span> American microbiologist

Edward Thomas Ryan is an American microbiologist, immunologist, and physician at Harvard University and Massachusetts General Hospital. Ryan served as president of the American Society of Tropical Medicine and Hygiene from 2009 to 2010. Ryan is Professor of Immunology and Infectious Diseases at the Harvard T.H. Chan School of Public Health, Professor of Medicine at Harvard Medical School, and Director of Global Infectious Diseases at the Massachusetts General Hospital. Ryan's research and clinical focus has been on infectious diseases associated with residing in, immigrating from, or traveling through resource-limited areas. Ryan is a Fellow of the American Society of Microbiology, the American Society of Tropical Medicine and Hygiene, the American College of Physicians, and the Infectious Diseases Society of America.

<span class="mw-page-title-main">MCR-1</span>

The mobilized colistin resistance (mcr) gene confers plasmid-mediated resistance to colistin, one of a number of last-resort antibiotics for treating Gram-negative infections. mcr-1, the original variant, is capable of horizontal transfer between different strains of a bacterial species. After discovery in November 2015 in E. coli from a pig in China it has been found in Escherichia coli, Salmonella enterica, Klebsiella pneumoniae, Enterobacter aerogenes, and Enterobacter cloacae. As of 2017, it has been detected in more than 30 countries on 5 continents in less than a year.

Dipshikha Chakravortty is an Indian microbiologist, molecular pathologist and a professor at the department of Microbiology and Cell Biology at the Indian Institute of Science. Known for her studies on Salmonella and antibacterial resistance, Chakravortty is an elected fellow of the National Academy of Sciences, India, the Indian Academy of Sciences and the Indian National Science Academy. The Department of Biotechnology of the Government of India awarded her the National Bioscience Award for Career Development, one of the highest Indian science awards, for her contributions to biosciences, in 2010. Prof. Chakravortty has been elected as an prestigious INSA Council member, which will be functional from January 2024 Prof Chakravortty is among the top3% of the Scientists in India https://www.adscientificindex.com/scientist/dipshikha-chakravortty/298893

<span class="mw-page-title-main">History of typhoid fever</span>

In 2000, typhoid fever caused an estimated 21.7 million illnesses and 217,000 deaths. It occurs most often in children and young adults between 5 and 19 years old. In 2013, it resulted in about 161,000 deaths – down from 181,000 in 1990. Infants, children, and adolescents in south-central and Southeast Asia experience the greatest burden of illness. Outbreaks of typhoid fever are also frequently reported from sub-Saharan Africa and countries in Southeast Asia. In the United States, about 400 cases occur each year, and 75% of these are acquired while traveling internationally.

Melita Alison Gordon is a gastroenterologist who works on invasive gut pathogens and tropical gastrointestinal disease. She leads the Malawi Liverpool Wellcome Trust Salmonella and Enterics Group. Gordon was awarded the British Society of Gastroenterology Sir Francis Avery Jones Research Medal in 2011.

References

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