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Line 1: − <big><center>[[Enterobacteriaceae|'''BACK TO ENTEROBACTERIACEAE''']]</center></big>+ − <big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big> − <big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big> − *Some serotypes tend to be more species specific, whereas others can affect a wide range of species. For example: − * '''''Salmonella enteritidis''''' − * '''''Salmonella typhimurium''''' − ** Widespread in most species. − * '''''Salmonella dublin''''' − * Cattle − * '''''Salmonella cholerae suis''''' − ** Pigs − ** Usually speticaemic. − ** A cause of [[Intestines - Ulcerative Enteritis|ulcerative enteritis]] in the pig. − ** Not very common now. − * '''''Salmonella montevideo ''''' − ** Produces outbreaks from contaminated imported meat and bone meal. + − + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
→Clinical infections
Salmonella spp. are gram-negative straight rods, usually flagellated, facultative anaerobes.
===Overview===
* [[Intestines - Fibrinous/ Haemorrhagic Enteritis#Salmonellosis|Salmonellosis]]
*Important member of the enterobacteria
*Cause disease in humans and animals worldwide
*Reservior of infection in poulty, pigs, rodents, cattle, dogs
*Bacteria may be present in water, soil, animal feed, raw meat
*Cause enteritis and systemic infection (septicaemia and abortion)
*''Salmonella'' may be carried sub-clinically
*Some human strains cause enteric fever (''S. Typhi'' causes typhoid), also gastroenteritis, septicaemia or bacteraemia
===Characteristics===
*Gram negative bacilli
*Facultative intracellular pathogens
*Non-lactose fermentors, oxidase negative
*Do not produce urease or indole from tryptophan
*Utilise citrate as a carbon source
*Reduce nitrates to nitrites
*Grow on MacConkey
*Red colonies on brilliant green agar indicating alkalinity
*Ferment glucose to produce acid and gas
*Usually produce hydrogen sulphide - red colinies with black centre on XLD agar
*Most motile with flagellae (H antigen)
*H antigen can be in phase 1 or phase 2, depending on a genetic switch allowing for one of the H antigen genes to be transcribed at any one time
===Classification===
*Single species, ''Salmonella enterica''
*Over 2400 pathogenic serotypes or serovars identified
*Grouped into 9 groups according to Somatic, O antigen (lipopolysaccharide) by the Kauffmann-White scheme - determined by slide agglutination of the bacteria with specific antisera
*Categorised into serovars depending on and H (Flagellar) antigen, e.g. ''Salmonella enterica'' subspecies ''enterica'' serovar Tymphimurium; must also determine phase of H antigen (isolates must be in phase 1 to be typed)
*Most animal and human isolates in Groups B to E
===Pathogenicity===
*Faecal-oral transmission
*Infection frequently transmitted from faeces of rodents and birds
*Young, immunocompromised animals particularly susceptible
*Comparitively large dose required for infection due to gastric acid, normal intestinal flora and local immunity
*Enterocolitis:
**Acute enteritis
**Bacteria adhere to intestinal epithelial cells in the ileum and colon, probably via fimbrae, O antigen and flagellar H antigen
**Multiply in and destroy epithelial cells
**Cytotoxin may cause epithelial cell damage by inhibiting protein synthesis and causing calcium escape from cells
**Enterotoxin may induce fluid secretion into intestinal lumen
**Degeneration of microvilli
*Systemic disease:
**Bacteria invade and replicate in host cells and resist phagocytosis and destruction by complement
**Bacteria internalised by intestinal epithelial cells by inducing ruffling of cell membranes and uptake into vesicles
**The organisms replicate within the vesicles and are released from the cells
**Stimulate immune response on reaching the lamina propria
**Acute inflammation, possibly with ulceration; prostaglandin and cytokine production by epithelial cells; enterotoxin production damaging mucosa
**Phagocytosis of bacteria by [[Neutrophils|neutrophils]] and macrophages
**Bacteria either destroyed by the phagocytic cells or survive and multiply in the cells to cause systemic disease
**Resistance to phagocytosis and destruction by complement allows spread within the body - bacteraemia and septicaemia
**LPS O antigens prevent damage to bacterial cell wall by complement
**LPS also causes endotoxaemia, and may contribute to local inflammatory response damaging intestinal cells to cause diarrhoea
**Endotoxic shock during septicaemic [[Salmonellosis|salmonellosis]] due to LPS
**Septicaemia may cause [[Bacterial skin infections - Pathology#Systemic bacterial infections|cyanosis of extremities]]
**Intracellular carriage if bacteria no completely removed
**Invasive potential of certain strains e.g. ''Salmonella'' Dublin associated with carriage of a large plasmid, encoding genes to allow intracellular survival in macrophages and also to allow iron acquisition
**''Salmonellae'' are facultative intracellular organisms, allowing them to move from the gut in macrophages and cause a bacteraemia and lesions throughout the body
**Possession of Pathogenicity Islands associated with virulence
*Carriage:
**''Salmonellae'' can persist in the gut or gall bladder
**Excreted in faeces after clinical signs disappeared - active carriage
**Bacteria can survive intracellularly, avoiding the immune system and antimicrobials
**May have latent carriage and intermittent excretion in faeces
**Stresses e.g. transportation, illness, parturition, overcrowding promote excretion in carrier animals and may cause clinical signs to be shown
**Tortoises, terrapins, snakes and other reptiles ofter carry ''Salmonellae''
**Asymptomatic carriage allows faecal spread of infection
===Clinical infections===
*Zoonotic
*Most human infections contracted from animals, especially poulty and cattle
*Some serotypes are host-specific, some infect a wide range of species
*Healthy adult carnivores are resistant to [[Salmonellosis|salmonellosis]]
*Clinical outcome depends on number of bacteria ingested, virulence of serotype, susceptibility of host
*Young and debilitated animals susceptible
*''Salmonella'' serotypes:
**''S.'' Typhimurium infects many species; causes severe diarrhoea; non-invasive; causes of food poisoning in humans, e.g. from infected poultry
**''S. enteritidis'': non species-specific; losses in young birds; causes food poisoning in humans
**''S.'' Dublin: invasive serovar; infects cattle
**''S.'' Cholerae-Suis: primarily infects pigs; also causes severe human disease
**''S.'' Pullorum: infects poultry; egg-transmitted; causes bacillary white diarrhoea, known as pullorum disease
**''S.'' Gallinarum: infectes older birds; known as fowl typhoid
**''S.'' Abortis-ovis: infects sheep
**''S.'' Abortus-equi: infects horses outside of the UK
**''S.'' Typhi, ''S.'' Paratyphi: infect humans
**''S.'' Montevideo produces outbreaks from contaminated imported meat and bone meal
*Enteric [[Salmonellosis|salmonellosis]]:
**Enterocolitis occurs in most farm animal species affecting all ages
**[[:Category:Enteritis, Ulcerative|Ulcerative enteritis]]
**Fever, depression, anorexia, foul-smelling diarrhoea containing blood, mucus and epithelial casts
**Dehydration and weight loss
**Abortion
**Fatal within days in severely young animals
**Milder syndrome where endemic on farms, possibly due to acquired immunity
**Chronic enterocolitis can occur in surviving pigs, cattle, horses, causing intermittent fever, soft faeces and gradual weight loss
*Septicaemic [[Salmonellosis|salmonellosis]]:
**Most common in calves, neonatal foals, pigs under one month
**Sudden onset fever, depression, recumbency
**Die within 48 hours if not treated
**Persistent diarrhoea, meningitis, arthritis or pneumonia may occur in surviving animals
**Found in [[Infectious Arthritis#In Horses|arthritis of horses]]
**Can cause haemorrhagic disease by [[Platelet Abnormalities|secondary thrombocytopenic disease]]
**''S.'' Cholerae-Suis in pigs causes blue discoloration of ears and snout; co-infection with viruses causes severe clinical forms of disease
*Bovine [[Salmonellosis|salmonellosis]]:
**Syndrome of fever and diarrhoea (with dysentery), often fatal, in calves and adult cattle
**Abdominal pain in adult cattle due to necrotic bowel
**Recumbency and depression, with death after 7-10 days during severe infection - mortality up to 75% in untreated adult animals
**Antibiotic treatment reduces mortality to 10%
**Diarrhoea lasts for up to 2 weeks, and complete recovery may take months
**May cause abortion of pregnant cattle in absence of other signs
**Septicaemia in neonates; accute enteritis in older calves
**Calves are dull, lethargic, inappetent, pyrexic, with profuse, fowl-smelling diarrhoea
**Death in calves can occur after 2-3 days
**Diarrhoea in survivors may last 2 weeks
**Caused by infection with various ''Salmonella'' serotypes, e.g. ''S.'' Dublin and ''S.'' Typhimurium
**An important zoonosis and reportable
**Carrier animals important for spread
**''Salmonella'' Dublin:
***Causes enterocolitis with blood-stained, foul-smelling diarrhoea containing mucus and epithelial cells
***Can cause fatal septicaemia - fever, depression, drop in milk yield; calves may develope arthritis, meningitis, pneumonia
***Abortion with no other clinical signs
***Chronic infections with ''S.'' Dublin in calves cause dry gangrene of extremities due to disseminated intravascular coagulation; tips of ears, tail and limbs may slough
***Can cause [[Osteomyelitis|Osteomyelitis]] in young animals
***Most survivors become subclinical excretors
***May become latent carriers with no excretion
*<div id="Spleen">[[Salmonellosis|Salmonellosis]] in poultry:
**''S.'' Pullorum and ''S.'' Gallinarum now rare in UK due to eradication programs including the Pullorum test (whole blood slide agglutination to detect antibody to both ''S.'' Pullorum and ''S'' Gallinarum)
**These ''Salmonellae'' can infect the ovaries of hens and be transmitted via eggs
**Pullorum disease infects young chickens and turkeys (under 3 weeks); high mortality rates; anorexia, depression, white diarrhoea; white nodules throughout lungs; focal necrosis of liver and [[Spleen - Anatomy & Physiology|spleen]]</div>
**Fowl typhoid causes similar lesions to pullorum disease in young birds; septicaemic condition in adult birds with sudden death (enlarged, friable, bole-stained liver and enlarged [[Spleen - Anatomy & Physiology|spleen]]). On post mortem inspection bronzing of the organs is notable.
**Paratyphoid caused by non host-specific ''Salmonella'' serotypes, e.g. ''S.'' Enteritidis and ''S.'' Typhimurium; often subclinical infections
===Diagnosis===
*History of previous outbreaks; clinical signs
*Post mortem: enterocolitis; blood-stained intestinal contents; enlarged mesenteric lymph nodes
*Laboratory confirmation by detection in faeces and blood from live animals; intestinal contents and tissue samples from dead animals
*Isolation from blood or tissues confirms septicaemic salmonellosis
*Heavy growth on plates innoculated with faeces or intestinal contents from infected animals suggests ''Salmonella'' as cause
*Light growth may suggest carrier state
*Culture specimens on BG and XLD agar; also add to enrichment broth such as selinite or tetrathionate broth; incubate plates and broth under aerobic conditions at 37 degrees centigrade for 48 hours; subculture from enrichment broth at 24 and 48 hours
*Suspicious colonies should be identified biochemically by reactions in TSI agar and lysine decarboxylase
*Slide agglutination using antisera for O and H antigens confirm the serotype
*The antigens in both phases of the H antigen must be identified
*Phage typing is used for epidemiological studies of isolates
*A rising antibody titre using paired serum samples in ELISA indicates active infection
===Treatment===
*Intravenous antibiotics used to treat septicaemic salmonellosis
*Effective antimicrobials include tetracyclines, chloramphenicol, trimethoprim-sulphonamides, ampicillin, amoxicillin, 3rd generation cephalosporins, fluoroquinolones, but depend on the susceptiblity of individual isolate
*Fluid and electrolyte replacent to prevent dehydration and shock
===Control===
*Reduce exposure of young animals from fomites, food, water, infected animals
*Avoid stresses e.g. overcrowding
*Purchase animals from reliable sources and isolate incoming animals
*Separate animals according to age
*Rodent control, good hygiene, pasture rotation
*Avoid grazing animals on pasture fertilised by slurry for at least 2 months after spreading
*Attenuated live ''S.'' Typhimurium and ''S.'' Dublin vaccines used in cattle
*Avoid oral prophylactic antimicrobials
==In Reptiles==
It is estimated that between 36 and 77% lizards harbour Salmonella - the most recognized reptilian zoonosis. Owners must be educated regarding the public health hazard (especially for the very young, the old and the immune compromised).
[[Category:Lizard_and_Snake_Glossary]]
[[Category:Enterobacteriaceae]]
[[Category:Zoonoses]]
[[Category:To_Do_-_Bacteria]]