L11 Salmonella Flashcards
What disease does Salmonella spp. cause?
Food poisoning, typhoid
How does Salmonella cause disease?
Invasion, localised or systemic, T3SS
Features of Salmonella?
- Highly related (90%) to E. coli
- Gram neg
- Motile
- Facultative
- Also fairly related to Shigella
Which type of Salmonella covers all the traditional species?
Salmonella enterica
What is the most common strain of Salmonella in developed countries?
Salmonella enterica Serovar Enteritidis
What condition does S. enterica cause?
Gastroenteritis (Salmonellosis)
What are the symptoms of salmonellosis?
Nausea, vomiting, pain, diarrhoea, fever
Salmonella is a leading cause of foodborne disease - 2nd only in Western World to?
Campylobacter
What food is Salmonella particularly associated with?
Poultry & eggs
Classification of Salmonella?
> 2,500 serovars (based on O and H antigens)
1,500 in S. enterica enterica
2 types of Salmonella enterica?
Typhoidal and non-typhoidal
2 types of typhoidal Salmonella?
S. typhi and S. paratyphi
2 types of non-typhoidal Salmonella?
S. typhimurium and S. enteritidis
What disease does typhoidal Salmonella cause?
Typhoid & paratyphoid fevers (humans)
What disease does non-typhoidal Salmonella cause?
Gastroenteritis & extraintestinal (humans & animals)
Most foodborne salmonellosis results in?
Gastroenteritis
Spectrum of diarrhoea in gastroenteritis from?
from watery to dysentery (blood & mucus in diarrhoea - severe)
True or False: Gastroenteritis infection is most often self-limited (non-invasive)
True
Is S. enteritidis important in causing foodborne outbreaks in developed or developing countries?
Developed
What causes typhoid (enteric) fever?
S. typhi
What new disease is emerging from S. typhimurium?
Invasive non-typhoidal salmonellosis
particularly in sub-Saharan Africa, predisposed by co-infection i.e. HIV, malaria
What are pathogenicity islands?
Mobile regions of DNA that have been acquired by bacteria and generally encode virulence factors
What is Salmonella typhimurium distinguished by on its genome?
Pathogenicity islands
What are the 2 Salmonella pathogenicity islands?
SPI1 and SPI2 - both encode T3SS (secrete different effector proteins)
When is SPI1 involved?
More involved earlier on (invasion)
When does SPI2 function?
After the cells have invaded and are found inside the target cell.
SPI2 becomes more dominant in systemic spread and later stages
Pathogenesis of invasive disease (S. enterica typhimurium)?
- Infect epithelial cells of SI
- Get a ‘splash effect’ due to rearrangement of actin within host cell
- T3SS: SPI1
- Grow within vesicle (Salmonella-containing vacuole), do not enter cytoplasm
- Apoptosis of epithelial cells
- Virulence plasmids involved
True or False: Salmonella is restricted in Salmonella-containing vacuole
True. Listeria and Shigella both rupture vacuole membrane. Salmonella in SCV → host cell eventually dies → apoptosis occurs → bacteria released
Salmonella entry into host cells is mediated by?
SPI1 T3SS and its effectors
What is a unique characteristic of Salmonella pathogenesis?
Splash effect
Histopathology of S. enteritidis?
Denuded epithelium & destruction of villi. This damage attracts inflammatory cells. Salmonella will eventually kill epithelial cell, which contributes to gastroenteritis
What is the role of the T3SS encoded by SPI2?
Bacteria inject proteins into macrophage cytosol → phagosome doesn’t develop normally but instead forms SCV - a privileged and nutrition-rich niche. This facilitates spread as macrophages move on to liver/spleen/LNs throughout the body. Eventually macrophages die, allowing Salmonella to invade other tissues (dissemination) → systemic disease
The plasmid involved in virulence (pSLT) encodes what locus?
spvRABCD locus - encodes SpvB:ADP-ribosylating toxin - requires SPI2 T3SS. Associated with non-typhoidal salmonellosis
Virulence factors in Salmonella?
- SPIs (SPI1 & SPI2 best studied)
- Plasmid (spv locus)
- Adhesins
- Flagella and chemotaxis
- LPS (contributes to inflammation which results in tetrathionate production)
What genes does SPI2 encode?
ttrRSBCA genes - allow use of tetrathionate reduction as a terminal electron acceptor, which allows Salmonella to respire in the gut (unusual because bacteria usually ferment in stomach)
What genes allow Salmonella to respire in the gut, and how?
ttrRSBCA genes - allow use of tetrathionate reduction as a terminal electron acceptor
S. typhi causes typhoid fever. What are the associated symptoms?
High fever, flushed appearance, chills, convulsions, delirium
How can survivors of typhoid fever excrete the organism for prolonged periods?
Bacteria create a reservoir in the gallbladder - excrete continuously in faeces
Pathogenesis of typhoid fever?
S. typhi cells enter the blood stream via M cells, multiply in the liver & spleen, and then re-enter the blood in high numbers
What is the main difference between S. typhimurium and S. typhi?
S. typhimurium enters via macrophages, S. typhi enters via M cells
Virulence factors of S. typhi?
Thought to be extremely complicated (as many as 200 genes) Vi antigen (survival in macrophages, serum resistance) Typhoid toxin (atypical A-B toxin, only produced in SCV)
Treatment for Salmonella infection?
Antibiotics contraindicated for salmonellosis, essential for typhoid.
Can also have gallbladder surgery in long-term carriers of S. typhi
Why are antibiotics contraindicated for Salmonellosis?
Antibiotics release LPS from dying Salmonella cells, inducing severe fever/shock
