salmonella Flashcards
salmonella: the organism
- gram-negative, flagellated, facultative anaerobe, rod-shaped
- member of the enterobacteriaceae
- differentiated serologically by:
-> O - LPS
-> H - flagella
-> Vi - capsule antigens - over 2000 serovars each previously considered a separate species
- reclassified intro 2 species: salmonella enterica and salmonella bongori
salmonella infection
- infect a broad range of hosts: humans, mammals, birds, reptiles and insects
- estimates from the CDC anually in the USA salmonella causes:
- 1.35 million infectiond
- 26,500 hospitalisations.
- 420 deaths
- food is the source of infection for most cases
- focus on 2 serovars:
- S.enterica serovar typhimurium
- S.enterica serovar typhi
S.enterica serovar typhimurium
can cause:
- gastroenteritis in humans, lethal diarrhoea in calves
- systemic disease in genetically susceptible mice
S.enterica serovar typhi
can cause:
- systemic infection in humans only
S.typhimurium infections
- major cause of gastroenteritis in the developed world
- consumption of contaminated food is major source of infections
- contact with reptiles and amphibians can also lead to infection
- colonisation of farm animals generally asymptomatic - difficult to identify contaminated animals and eradicate form food chain
salmonella typhi infections
- the typhi is very rare in this country or Higher income countries.
- over the first part of the last century the numberof cases decreased rapidly and that’s largely due to sanitation gain
the percentage of cases that are attributed to travel have risen.
- So they’re almost all typhi cases in the America and likely other as comparable High income countries are due to imported cases.
- So where people travel to parts of the world where rates of infection are much higher and then import those infections.
- So largely typhi has been dealt with in higher income countries.
slamonella typhi cases
So Salmonella Typhi is a global pathogen.
Is still highly significant.
- estimated 20 million typhoid cases annually with 200,000 deaths
infection outcomes with typhmurium
gastroenteritis
- infection localised
- short incubation period (12-72 hours)
- nausea, vomiting, abdominal pain, diarrhoea, fever
- characterised by a vigorous inflammatory response with sever neutrophil infection
- infection lasts under 10 days
infection outcomes with typhi
typhoid fever
- infection disseminated - intestine to liver, spleen and bone marrow
- longer 10-14 day incubation period
- non specific flu-like symptoms
- limited neutrophil influx, infiltrate mainly mononuclear cells (macrophages and dendritic cells)
- infection lasts 4 weeks if untreated and can lead to carrier state within bile duct with excretion in urine/ faeces for years
typhoid carrier - Mary
- asymptomatic carrier of S.typhi but worked as a cook
- refused to recognise that she was cause of typhoid outbreaks and was forcibly quarantined
- released in 1910 and continues to work as a cook causing more outbreaks and deaths
- quarantined in 1915 and died in quarantine of pneumoniae age 69 in 1938
- S.typhi found in gall bladder at autopsy
- in total caused 47 infections and 3 deaths
what happens when salmonella enterica serovars Typhimurium and typhi interact with the host
the intestinal epithelial cells that line the gut are the first cells that the bacteria will come into contact with
And then we have a different type of cell in the gut called M cells or microfold cells and they are evolved to capture content from the Lumen and present them to the innate immune system
- so when salmonella interacts with these M cells, it’s taken up By those cells into a vacuole and then it interacts and is presented to cells of The Host Innate immune system
- So of they’re able to trancytose across this barrier and emerge beneath the epithelial cells here. Then they will come into contact with all of these types of cells that have been recruited by the sensing innate immune system.
M cells
specialised epithelial cells associated with mucosal lymphoid tissue that can transcytose luminal antigens including microbes that can then be presented to phagocytic immune cells
polymorphonuclear leukocyte (PMN)
a type of granulated white blood cells including neutrophils, eosinophils and basophils
differing outcomes when salmonella enterica serovars Typhimurium and typhi interact with the host
gastroenteritis - non typhoidal salmonella serovars induce a more localised inflammatory response in which PMNs are recruited and enter the gut lumen resulting in diarrhoea
enteric fever- typhoidal salmonella serovars are disseminated by intestinal macrophages through the reticuloendothelial system onto the lymph nodes, liver and spleen.
- can survive in the macrophages and hide in them
how does salmonella enterica serovar typhi persist within hosts
We get ingestion through M cells, presentation to a macrophage, taken up into your macrophage within a vacuole and then survival within this vacuole.
- Now most bacteria that are taken up into a macrophage will be destroyed because it’s incredibly hostile environment.
- salmonella is able to avoid this outcome.
Within These macrophages and through the lymph they can travel to the mesenteric lymph nodes onto the spleen and the bone marrow onto the liver and into the gallbladder.
So this formation of a carrier State once the initial round of symptoms of resolved then patients will become asymptomatic and will think the infection has been cleared but it hasn’t and from the gallbladder it’s relatively straightforward to reseed the Lumen through the bile, therefore Releasing more salmonella typhi into the environment through the feces
So the carrier State leads to recurrence release of salmonella typhi into the environment.
