Difference between revisions of "Salmonella"
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<big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big> | <big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big> | ||
<big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big> | <big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big> | ||
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===Overview=== | ===Overview=== | ||
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*Zoonotic | *Zoonotic | ||
| + | *Outbreaks from contaminated imported meat and bone meal | ||
*Some serotypes are host-specific, some are not | *Some serotypes are host-specific, some are not | ||
*''S.'' Tymphimurium infects many species; causes severe diarrhoea; non-invasive; causes of food poisoning in humans, e.g. from infected poultry | *''S.'' Tymphimurium infects many species; causes severe diarrhoea; non-invasive; causes of food poisoning in humans, e.g. from infected poultry | ||
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*''S.'' Typhi, ''S.'' Paratyphi: infect humans | *''S.'' Typhi, ''S.'' Paratyphi: infect humans | ||
*Most human infections contracted from animals, especially poulty and cattle | *Most human infections contracted from animals, especially poulty and cattle | ||
| + | *A cause of [[Intestines - Ulcerative Enteritis|ulcerative enteritis]] in the pig. | ||
| + | *[[Intestines - Fibrinous/ Haemorrhagic Enteritis#Salmonellosis|Salmonellosis]] | ||
| + | *Can cause haemorrhagic disease by [[General Pathology - Haemostasis#Secondary Thrombocytopenic Disease|secondary thrombocytopenic disease]]. | ||
| + | *''Salmonella'' in [[Bones - inflammatory#Osteomyelitis|Osteomyelitis]] | ||
| + | * In [[Joints - inflammatory#In Horses|arthritis of horses]] | ||
===Diagnosis=== | ===Diagnosis=== | ||
Revision as of 19:21, 16 February 2008
Overview
- Important member of the enterobacteria
- Cause disease in humans and animals
- Reservior of infection in poulty, pigs, rodents, cattle, dogs
- 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 fermentor, oxidase negative
- Do not produce urease or indole from tryptophan
- Utilise citrate as a carbon source
- Reduce nitrates to nitrites
- Grow on MacConkey
- Ferment glucose to produce acid and gas
- Usually produce hydrogen sulphide
- 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 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
Pathogenesis
- Faecal-oral transmission
- Comparitively large dose required for infection due to gastric acid, normal intestinal flora and local immunity
- Enterocolitis:
- Acute enteritis
- Bacteria multiply in the intestine and damage epithelial cells
- Cytotoxin may cause epithelial cell damage
- Enterotoxin may induce fluid secretion into intestinal lumen
- Degeneration of microvilli
- Systemic disease:
- Bacteria internalised by intestinal epithelial cells
- Stimulate immune response on reaching the lamina propria
- Inflammatory response with phagocytosis of bacteria by neutrophils and macrophages
- Bacteria either destroyed by the phagocytic cells or survive and multiply in the cells to cause systemic disease
- Intracellular carriage if bacteria no completely removed
- Invasive potential of certain strains e.e 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, avioding the immune system and antimicrobials
- May have latent carriage and intermittent excretion in faeces
- Stress promotes excretion in carrier animals
- Tortoises, terrapins, snakes and other reptiles ofter carry Salmonellae
- Asymptomatic carriage allows faecal spread of infection
Clinical infections
- Zoonotic
- Outbreaks from contaminated imported meat and bone meal
- Some serotypes are host-specific, some are not
- S. Tymphimurium 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 howl typhoid
- 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
- S. Abortis-ovis: infects sheep
- S. Abortus-equi: infects horses outside of the UK
- S. Typhi, S. Paratyphi: infect humans
- Most human infections contracted from animals, especially poulty and cattle
- A cause of ulcerative enteritis in the pig.
- Salmonellosis
- Can cause haemorrhagic disease by secondary thrombocytopenic disease.
- Salmonella in Osteomyelitis
- In arthritis of horses