Salmonella

Year 1 - Semester 2

general features of salmonella

gram-negative, facultative anaerobe, most servers are motile, don’t ferment lactose and produce hydrogen sulphide, main reservoir is intestinal tract, facultative intracellular pathogen

is salmonella gram-negative or gram-positive?

gram negative

Which family does salmonella belong to?

enterobacteriaceae

What are the 4 groups used to classify salmonella?

genus, species, subspecies and serotypes/serovars

phage typing

method used to identify and differentiate specific strains of bacteria by observing their susceptibility to infection by various bacteriophages

What is a common method of identifying the specific serovar of salmonella present?

phage typing

What is the veterinary significance of salmonella?

subclinical carriage and shedding in the environment by domestic and wild species, hazard of meat contamination in food producing animals, vertical transmision to eggs, foetus and milk, causes enteric disease in companion animals which is more common now due to raw diets, causes enteritis, enterocolitis, septicaemia, abortion and systemic disease in food producing animals

What are the 3 main types of salmonella serovars?

generalist, host adapted, host restricted

pathogenesis of salmonella enteric disease

1. bacteria responds to gastric acidic environment through a complex adaptive system

2. organisms that survive low pH environment proceed to the lumen of the intestines

3. bacteria compete with gut microflora to make initial contact with enterocytes and M cells of Peyer’s patches using flagella and fimbriae present on the bacterial cell surface

4. after adhesion, the bacteria are internalised through uptake via phagocytosis or active invasion of enterocytes/phagocytes

5. this causes an inflammatory response

What are the virulence factors of salmonella which cause enteric disease?

salmonella pathogenicity islands

How many salmonella pathogenicity islands are there?

18

How does salmonella enter enterocytes?

ruffling host cell membranes and bacterial uptake into large vesicles

What happens once salmonella has entered enterocytes?

salmonella replicates inside vesicles which allows it to resist cell-mediated degradation, infected cells release pro-inflammatory cytokins which causes diarrhoea

How do host cells sense pathogen associated molecular patterns?

pattern recognition receptors

What is the innate immunity host response to salmonella infection?

pattern recognition receptors sense PAMPs which influences maturation of phagosomes, triggers signalling pathways which modulate the inflammatory cascade and modulates gene of expression, all of these processes further activate the immune response

what do toll-like receptors in host cells detect?

pathogen-associated molecular patterns like lipopolysaccharides and flagellin located on the cell surface or within phagosomes

What happens to salmonella once it has entered M cells in Peyer’s patches of the intestines?

1. the bacteria are carried to the regional mesenteric lymph node for presentation to the macrophages

2. non-invasive salmonella is usually cleared here but invasive salmonella producing septicaemia and systemic disease can resist clearance, survive and replicate within the macrophages

3. these salmonella hide within macrophages and are disseminated from the mesenteric lymph node via the lympho-reticular and vascular systems to the liver, spleen and other organs

T3SS SPI2

a critical virulence mechanism in salmonella that enables intracellular survival and replication within host cells, particularly macrophages

Which salmonella pathogenicity island allows invasive salmonella to resist clearance by macrophages and cause systemic disease?

T3SS SPI2

How do typhoidal salmonella serovars survive?

they have specific features which prevent them from being recognised by the immune system (TLR4)

What are the different mechanisms that typhoidal salmonella serovars use to evade recognition by the immune system?

capsule presents lipopolysaccharide or flagella from being recognised, can switch on/off expression of flagellar genes, some don’t have flagella

Which serotypes of salmonella cause typhoid-like infections?

gallinarum, pullorum, choleraesuis, dublin

Which serotypes of salmonella cause typhoid-like infections in poultry?

S. gallinarum and S. pullorum

Which serotype of salmonella causes typhoid-like infection in pigs?

S. choleraesuis

Which serotype of salmonella causes typhoid-like infection in cattle?

S. Dublin