Samonella and Salmonelosis

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What is salmonells

Facultative anaerobic gram negative rod

Member of eneterobacteriacae

Discovered in 1885 in pigs

Genus consists of 2 species

Salmonella bongori (Reptiles)

Salmonella enterica (All warm blooded species)

Major food borne zoonoses

Major cause of enteritis in humans and other animals

Major pathogen causing systemic disease in animals and humans (Typhoid fever)

Veterinary significance

Carried in intestines of food producing animals leading to meat contamination

Vertical transmission to eggs and milk

Disease of production animals

Diarrhoeal disease of companion animals

Broad host range salmonella

Causes inflammatory response and invasive gastroenteritis in humans, dogs, calves and pigs

Leads to influx of neutrophils

Damage to gut wall and invasion

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To get to the ileum salmonella must

Be able to deal with acidic pH with stomach

Has pumps to remove H+ ions and changes membrane structure

Cope with intestinal flow

Has adhesins called pili and fimbriae that allow adhesion to gut wall

Deal with low levels of oxygen

Facultative anaerobes so can growth with or without oxygen

How it causes gastroenteritis

Bacterium secretes proteins that alter host cell function and structure ???

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Type 3 secretion systems

T3SS are major virulence factors in gram negative bacteria

Salmonella contains 2

SPI1

Induces cytoskeletal changes in host epithelial cells - polymer???

SPI2

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Host innate immunity has developed receptors to quickly recognise pathogens as a danger

1st line of defence

Although adaptive immunity are more effective they are slow - 7 days or more to develope

Host must therefore recognise danger quickly

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Toll like receptors

Image

PAMP recognition leads to immune activation

Recognition of danger signal leads to production of signalling molecules- cytokines and chemokine activate the immune response

Flagella and limplysaccharide are PAMPs

Stealth and typhoidal infection

limited inflammation in gut invade by stealth by avoiding immune activation

This is achieved by hiding from recognition- the Vi capsule of S. Thyphiprevents LPS of flagella being recognised

Or by not having flagella

Intracellular survival

Adapted to survive in macrophages

Survival mode inside cells is important in development of systemic or typhoidal infection

Survival inside cells involves SPI2 T3SS which prevents the phagocytic ????

Mechanism of systemic infection

Entry via gut wall

Evidence of targeting lymphoid tisse

Salmonella invade underlying immune cells

Infected cells traffic via lymphatic system to spleen and liver

Intracellular replication - if uncontrolled ????

Carrier state infection

Persistent systemic infection without disease

Important is transmission as carrier appears healthy but can transmit infection

S.Thyphi in humans- persistence in gall bladder and shedding in faeces

S.Dublin shed in milk

S.Pullorum vertical transmission to chicks via egg