Salmonellosis Flashcards
What is salmonella?
Acute diarrohea infection caused by ingestion of food contaminated with bacterium belonging to genus Salmonella
What are the clinical symptoms of salmonella?
(4 marks)
- Stomach cramp
- Watery diarrhea
- Fever
- Vomiting
Why can there be some peaks seen across the average of Salmonella infections in europe?
- Increase in temperature in summer
Is salmonella gram negative or gram positive bacteria?
Gram negative
What species of salmonella affects humans?
Salmonella enterica
What is a serotype?
(4 marks)
- Group with single species of micro-organisms that share distinctive surface features i.e. bacteria/virus
- O antigens are distinguished by different chemical makeup
- H antigens are distinguished by protein content of the flagella
- Each H and O antigen has a unique code number
What are some of the subspecies of S. enterica?
(3 marks)
- Enterica (I)
- Salamae (II)
- Indica (VI)
3 More on slide/ notes
What are the top five serotypes of S. enterica that are responsible for human disease?
(5 marks)
- S. Enteritidis
- S. Typhimurium
- S. Infantis
- S. Stanley
- S. Newport
What agar’s can be used to indentify S. enterica?
(2 marks)
- Gram negative bacterium so use:
- Xylose-lysine deoxycholate agar (XLD)
- Brilliant green agar (BGA)
XLD on left
What happens once salmonella is put onto XLD agar?
(4 marks)
- Ferments xylose
- In fermentation, acidifies plate becoming yellow
- After xylose completely used up, only salmonella able to decarboxylate lysine in middle so media turns red (alkalisation)
- Salmonella metabolises thiosulfate so get production of hydrogen sulfide (black colony on middle image)
E.g. is middle image - alkalisation in B and acidification in C
What is a faculative anaerobe?
(2 marks)
- Organism that makes ATP by aerobic respiration if oxygen is present,* but capable of *switching to fermentation is oxygen isn’t present
- e.g. Salmonella enterica - spread across test tube but will gather mostly at the top because aerobic respiration generates more ATP than fermentation (right tube)
What process (more so molecular) can be used to identify the exact serovar in S. enterica?
- Agglutination of polyvalent O and H
- Then carry out biochemical tests of Oxidase and Indole tests
What does an oxidase test determine?
(2 marks)
- Used to identify bacteria that produce cytochrome c
- Can be used to identify gram negative bacili
What is the indole test used to determine?
(2 marks)
Dertermines if an organism has the ability to split amino acid tryptophan to form indole - positive test is indicated by red colour
For both gram positive and gram negative bacteria
What are zoonoses?
(2 marks)
Any disease or infection that is naturally transmissable from vertebrate animals to humans
May be bacterial or parasitic or may involve unconventional agents
What are food borne diseases?
(2 marks)
- Result of ingestion of food stuffs - contaminated with micro-organisms or chemicals
- Contamination can occur at any stage in process - can result from environmental contamination
- Including pollution of water, soil or air
What are ways of controlling Salmonella infections?
(3 marks)
- Rehydration - lots of fluids
- Manage fever - paracetamol
- Antibiotics - NO - except if bacteria reach blood streams or compromised immune system
Why isn’t loperamide used in controlling bacterial infections?
Prolongs diarrhea
What do the S. Tyhpimurium virulance factors do?
(4 marks)
- Aid in host colonisation
- Allows immune evasion
- Host/ predator destruction
- Nutrient scavenging
How does Salmonella infect the cell?
(2 marks)
- Invades either M cell or apical domain of epithelial cells
- Will cross and start to replicate inside host - either epithelial cell or M cell
What are M cells and what is their structure and function?
(6 marks)
- Microfold (M) cell
- Concentrated in bigger part of small intestine
- Phagocytes
- Basolateral pocket at its base w/ a macrophage next to it
- Everything absorbed by M cell is put into macrophage
- Salmonella bypasses^^ to get into macrophage
How does the T3SS work in Salmonellosis?
(5 marks)
- 2 parts
-
Spi 1:
- Bacteria in contact with non-phagocytic host cell, then forms injectosome and translocates forming pore in membrane
- Effector protein activates Cdc42, Rac & RhoG by mimicking function and exploiting them to enter cell
- After time passed bacteria inside express Spi 2 - works in exact same way as Spi 1 - uses own effector SifA to disrupt SCV
Formation of which structure leads to cell invasion?
Macropinocytic membrane - extension is loosely attatched to bacteria which eventually leads to bacterial internalisation
How does bacterial proliferation occur?
- Bacteria goes further inside and forms serovar containing vacule:
- SCV recognised by host cell destroyed xenophagy
- Or bcteria escapes vacuole, goes to cytoplasm but v inefficient, most of time bacteria detected and destroyed by host
- Most of time have maturation of SCV towards Golgi network & in golgi network will express Spi 2 protein
- Forms tubular domain creates a niche where bacteria will replicate a lot and eventually kill macrophage before infecting next one
