Difference between revisions of "Salmonella"

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*Important member of the enterobacteria
 
*Important member of the enterobacteria
*Cause disease in humans and animals  
+
*Cause disease in humans and animals worldwide
 
*Reservior of infection in poulty, pigs, rodents, cattle, dogs
 
*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)
 
*Cause enteritis and systemic infection (septicaemia and abortion)
 
*''Salmonella'' may be carried sub-clinically
 
*''Salmonella'' may be carried sub-clinically
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*Single species, ''Salmonella enterica''
 
*Single species, ''Salmonella enterica''
 
*Over 2400 pathogenic serotypes or serovars identified
 
*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
+
*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  
+
*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 
  
===Pathogenesis===
+
===Pathogenicity===
  
 
*Faecal-oral transmission
 
*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
 
*Comparitively large dose required for infection due to gastric acid, normal intestinal flora and local immunity
 
*Enterocolitis:
 
*Enterocolitis:
 
**Acute enteritis
 
**Acute enteritis
**Bacteria multiply in the intestine and damage epithelial cells
+
**Bacteria adhere to intestinal epithelial cells in the ileum and colon, probably via fimbrae, O antigen and flagellar H antigen
**Cytotoxin may cause epithelial cell damage
+
**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
 
**Enterotoxin may induce fluid secretion into intestinal lumen
 
**Degeneration of microvilli
 
**Degeneration of microvilli
 
*Systemic disease:
 
*Systemic disease:
**Bacteria internalised by intestinal epithelial cells  
+
**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
 
**Stimulate immune response on reaching the lamina propria
 
**Inflammatory response with phagocytosis of bacteria by neutrophils and macrophages
 
**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
 
**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
 +
**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 due to LPS
 
**Intracellular carriage if bacteria no completely removed
 
**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
 
**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
Line 58: Line 69:
 
**Bacteria can survive intracellularly, avioding the immune system and antimicrobials
 
**Bacteria can survive intracellularly, avioding the immune system and antimicrobials
 
**May have latent carriage and intermittent excretion in faeces
 
**May have latent carriage and intermittent excretion in faeces
**Stress promotes excretion in carrier animals
+
**Stresses e.g. transportaion, illness, parturition, overcrowding promote excretion in carrier animals
 
**Tortoises, terrapins, snakes and other reptiles ofter carry ''Salmonellae''
 
**Tortoises, terrapins, snakes and other reptiles ofter carry ''Salmonellae''
 
**Asymptomatic carriage allows faecal spread of infection  
 
**Asymptomatic carriage allows faecal spread of infection  

Revision as of 19:57, 16 February 2008

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Overview

  • 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 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 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
    • 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
    • Resistance to phagocytosis and destruction by complement allows spread within the body
    • 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 due to LPS
    • 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
    • Stresses e.g. transportaion, illness, parturition, overcrowding promote 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
  • Bovine Salmonellosis:
    • Syndrome of fever and diarrhoea (with dysentery), often fatal, in calves and adult cattle
    • May cause abortion of pregnant cattle in absence of other signs
    • Caused by infection with various Salmonella serotypes, e.g. S. Dublin and S. Typhimurium
    • An important zoonosis and reportable
    • Carrier animals important for spread
  • A cause of ulcerative enteritis in the pig.
  • Can cause haemorrhagic disease by secondary thrombocytopenic disease.
  • Salmonella in Osteomyelitis
  • In arthritis of horses

Diagnosis

Treatment

Control