Salmonella Flashcards
What is salmonella a member of and what group does it fit
Member of enterobacteriacae
Facultative anearobic Gram negative rod
What are the two genus of salmonella and how many subspecies does it have
Salmonella bongori (reptiles)
Salmonella enterica (all species)
2500 subspecies or serovars
What are the three reasons why salmonella is so important
1 - major food borne zoonoses
2 - major cause of enteritis in humans and other animals
3 - major pathogen causing systemic disease in animals and humans (typhoid fever)
Why is salmonella of veterinary importance
Carried in intestines of food producing animals leading to contamination of meat
Disease (systemic or gastroenteritis) of production animals
Vertical transmission to eggs and milk
Diarrhoeal disease of companion animals
What does broad host range salmonella cause
Causes inflammatory and invasive gastroenteritis in humans, dogs, calves and pigs
Leads to influx of neutrophils
Damage to gut wall and invasion may occur
Diarrhoea is thought to caused by fluid efflux due to ionic imbalance
Some species inflammation limited and bacteria can persist in intestines - chickens, cows and pigs
Where does pathology of salmonella occur and how does it get there
The ileum
Deal with stomach acid - has pumps to remove H+, changes membrane structure
Cope with intestinal flow - has Adhesins pili and fimbriae allow adhesion to gut wall
Deal with low levels of oxygen - facultative anaerobe
What is the mechanism of pathogenesis when salmonella causes gastroenteritis
The bacterium - secrete proteins alter host cell function and structure via machinery called a Type III secretion system allow invasion from gut and inflammation
The host - innate immune system recognises repeated features (flagella and lipopolysaccharide) of the bacterium by recognition receptors and initiate inflammatory response
What is salmonella type III secretion T3SS
T3SS are major virulence factors in Gram negative
Salmonella has two T3SS systems encoded on pathogenicity islands - SPI1 and SPI2
T3SS are bacterial machinery that deliver effector proteins or toxins to host cells via a need and syringe like structure
SPI1 and SPI2 play key roles in disease process in gut SPI2 in systemic infection
What does SPI1 induce
SPI1, TTTS induces cytoskeletal changes in host epithelial cells - polymerisation of actin leading to membrane ruffling and allowing cell invasion and causing inflammation
How has the host innate immunity developed to recognise pathogens as a danger
Innate immune system = 1st line of defence
Adaptive immunity more effective but slow 7+ days to develop
Host cells have pattern recognition receptors that recognise repeated structures on bacteria, viruses ect. We call PAMPs or pathogen associated molecular patterns
What are Toll-like receptors
Most important category of pattern recognition receptors
Found in most vertebrate species
Look at table in PowerPoint
How does PAMP recognition leads to immune activation
Recognition of danger signal leads to production of signaling molecules, cytokines and chemokines that activate the immune response
Flagella and lipolysaccharide (LPS) are main PAMPS of salmonella and induce an inflammatory immune response in host by recognition by TLR4 and TLR5 respectively
Why are typhoid all infections different to most salmonella’s
They have limited inflammation in gut - invade by stealth avoiding immune activation
Achieved by hiding from recognition - the Vi capsule of S. Typhi prevents LPS of flagella being recognised
Or by not having flagella (S. Gallinarum/S. Pullorum) or switching off flagellar genes S. Typhi to avoid TLR5 recognition
What are salmonella adapted for intracellular survival
Survive in macrophages
Important development of systemic or typhoidal infection
Survival inside cells involves SPI2 T3SS which prevent phagocytic vacuole fusing with antimicrobial vesicles
Salmonella may interfere with adaptive immune response and avoids antibody in cells
What are salmonella’s mechanism of systemic infection
Entry via gut targeting lymphoid tissue in gut
Salmonella invade underlying immune cells (macrophages and dendritic cells)
Infected cells travel via lymphatic system to spleen and liver
Intracellular replication in cells - may lead to septicaemia and death
Immune clearance can occur and animal recovers
Low persistent infection carrier state may develop
