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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
*Reservior of infection in poulty, pigs, rodents, cattle, dogs
*Reservior of infection in poulty, pigs, rodents, cattle, dogs
*Cause enteritis and systemic infection (septicaemia and abortion)
*Cause enteritis and systemic infection (septicaemia and abortion)
===Characteristics===
===Characteristics===
*Gram negative bacilli
*Facultative intracellular pathogens
*Facultative intracellular pathogens
*Non-lactose fermentor
*Non-lactose fermentor, oxidase negative
*Do not produce urease or indole from tryptophan
*Do not produce urease or indole from tryptophan
*Utlise citrate as a carbon source
*Utilise citrate as a carbon source
*Reduce nitrates to nitrites
*Grow on MacConkey
*Ferment glucose to produce acid and gas
*Usually produce hydrogen sulphide
*Usually produce hydrogen sulphide
*Most motile with flagellae (H antigen)
*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
*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===
===Classification===
===Pathogenesis===
===Pathogenesis===
*Faemcal-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 invade the body
**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
===Clinical infections===
===Clinical infections===