Salmonella Flashcards
(41 cards)
What does the severity of salmonella infections in humans vary based on?
- serotype
- Health status of the human host (e.g immunosuppression)
- Children under 5 and elderly people
Why are most strains of salmonella considered to be pathogenic?
They have the abilty to invade, replicated and survive in human host cells resulting in potentially fatal disease
How does salmonella gain access to host cells?
It induces its own phagocytosis in order to gain access to the host cells
What are salmonella pathogenicity islands (SPIs)?
Gene clusters located at the large chromosomal DNA region and endcoding for the structures involved in the invasion process.
- SPIs encode for type III secretion systems, multichanel proteins that allow Salmonella to inject its effectors across the intestinal epithelial cell membrane into the cytoplasm
- The bacterial effectors then activate the signal transduction pathway and trigger reconstruction of the actin cytoskeleton of the host cell, resulting in the outward extension or ruffle of the epithelial cell membrane to engulf the bacteria. The morphology of the membrane ruffle resembles the process of phagocytosis
What makes some Salmonella strains non-virulent?
Their lack of to ability persist in the host cell
What happens following following the engulfment of Salmonella into the host cell?
- The bacterium is encased in a membrane compartment called a vacuole, which is composed of the host cell membrane.
- Under normal circumstances, the presence of the bacterial foreign body would activate the host cell immune response, resulting in the fusion of the lysosomes and the secretion of digesting enzymes to degrade the intracellular bacteria.
- However, Salmonella uses the type III secretion system to inject other effector proteins into the vacuole, causing the alteration of the compartment structure.
- The remodelled vacuole blocks the fusion of the lysosomes and this permits the intracellular survival and replication of the bacteria within the host cells.
What does the capability of the bacteria to survive within macrophages allow for?
It allows them to be carried in the reticuloendothelial system (RES)
How are salmonella strains commonly grouped?
Typhoid Salmonella and non-typhoid Salmonella (NTS)
In human infections, what are the four different clinical manifestations?
- Enteric fever
- gastroenteritis
- bacteraemia
- other extraintestinal complications, and chronic carrier state
Clinical manifestations of Salmonella: Enteric fever
Salmonella Typhi is the aetiological agent of typhoid fever, while paratyphoid fever is caused by S. ParatyphiA, B and C. Since the clinical symptoms of paratyphoid fever are indistinguishable from typhoid fever, the term ‘enteric fever’ is used collectively for both fevers, and both S. Typhi and S. Paratyphi are referred as typhoid Salmonella
TRUE or FALSE: Humans are the sole reservoir for the two strains of typhoid Salmonella
TRUE
How are the two strains of typhoid Salmonella transmitted?
Via the ingestion of food or water contaminated with the waste of infected individuals
Enteric fever is characterized by an incubation period of
One week or more, with prodomal symptoms such as headache, abdominal pain and diarrhoea (or constipation), followed by the onset of fever
Diarrhoea is more commonly observed in children, whereas patients with immunosuppression are more likely to develop constipation
During the illness, enteric fever displays a specific fever pattern.
Describe this pattern
An initial low-grade fever (> 37.5°C to 38.2°C) which slowly develops to high-grade fever (> 38.2°C to 41.5°C) in the second week.
If the patient is left untreated, fever can persist for a month or more
What may infected patients develop besides fever?
Myalgia, bradycardia, hepatomegaly (enlarged liver), splenomegaly (enlarged spleen), and rose spots on their chest and abdomen
15% of the infected patients develop gastrointestinal complications which include
pancreatitis, hepatitis and cholecystitis
What is one of the most severe gastrointestinal complications?
Haemorrhage is one of the most severe gastrointestinal complications that occur as a result of perforation of Peyer’s patches, lymphatic nodules located at the terminal ileum, resulting in bloody diarrhoea
The ability of typhoid Salmonella to survive and persist in the RES results in relapse in what percentage of patients?
10%
Gastroenteritis Salmonella strains other than S. Typhi and S. Paratyphi are referred to as NTS. Where are they predominantly found?
in animal reservoirs
Clinical manifestations: NTS infections are characterized by gastroenteritis or ‘stomach flu
An inflammatory condition of the gastrointestinal tract which is accompanied by symptoms such as non-bloody diarrhoea, vomiting, nausea, headache, abdominal cramps and myalgias. Symptoms such as hepatomegaly and splenomegaly are less commonly observed in patients infected with NTS
TRUE or FALSE: Compared to typhoid infections, NTS infections have a Longer incubation period
Compared to typhoid infections, NTS infections have a shorter incubation period (6–12 h) and the symptoms are usually self-limiting and last only for 10 days or less
What do Gastrointestinal complications of NTS infections include?
Cholecystitis, pancreatitis and appendicitis, while the perforation of the terminal ileum has no association with NTS infections
Who are highly susceptible to NTS infections?
Infants, young children, elderly people and immunocompromised patients are highly susceptible to NTS infections and develop more severe symptoms than normal individuals
Clinical manifestations: Salmonella bacteraemia
A condition whereby the bacteria enter the bloodstream after invading the intestinal barrier.
Almost all the serotypes of Salmonella can cause bacteraemia, while S. Dublin and S. Cholearaesuis are two invasive strains that are highly associated with the manifestations of bacteraemia
