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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
*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
**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