Salmonella I Flashcards
What are the characteristics of salmonella?
Gram- member of enterobacteriaceae.
Isolated from intestines of wide variety of animals.
Two species of salmonella: enterica and bongeri
Two serotypes of human disease: enterica typhi and enterica typhimurium.
SptP is an effector of which virulence factor in salmonella typhimurium?
It’s an effector of SPI1. It is a GAP for cdc42/Rac and therefore stops membrane ruffling. SptP- mutant shows continuous membrane ruffling (early and late).
SopE alone=ruffling
SopE + sptP = no ruffling
In other words, sptP is important for reversing the effects of sopE/E2
What is the disease caused by salmonella typhimurium?
- Gastroenteritis (vomiting, diarrhea, etc)
- From food contaminated by infected animal
- bacteria colonize intestinal epithelium
- 1.4 million cases a year
- more severe systemic infection in mouse.
What is the disease caused by salmonella typhi?
- typhoid fever: 10% lethality if untreated
- food/water contaminated by infected humans
- no animal model–human specific
- systemic infection of blood, liver, spleen, gallbladder
- 14 million cases worldwide
- 1-5% asymptomatic like typhoid mary
What is the typhimurium pathogenic cycle in humans?
Enteritis:
- Adherence to M-cells, enterocytes
- Induction of membrane ruffling
- Internalization
- Growth in vacuole
- Spread within epithelium, inflammation
What is the typhimurium pathogenic cycle in mice?
Enteric fever:
- Transcytosis (get into cells and across them)
- Phagocytosis by macrophages
- Growth in vacuole
- Spread to liver, spleen, etc
What is the mode of infection of typhimurium orally vs IP?
Oral: pass thru enterocytes, M-cells ➡️macrophages➡️organs
IP: macrophages➡️organs
What are the genetic determinants of virulence in typhimurium?
- Salmonella pathogenicity islands (SPI1-10)
- virulence plasmid
What are salmonella pathogenicity islands?
SPI have different % G+C content than genome
- origin from horizontal gene transfer
- several genes that function together in pathogenesis
What is SPI1?
- encodes T3SSg
- important for invasion of epithelial cells
- SPI1- mutant = 50x higher LD50 orally but for IP, same LD50 as WT
- Inv ABC
- components of translocases or chaperones
- secreted effectors
- transcriptional regulators
- induce ruffling early, shut off ruffling late.
What is SPI2?
- encodes T3SS
- important for intracellular growth
- SPI2- mutant = much higher LD50 oral and IP infection.
What is SPI4?
- encodes T1SS that secreted SiiE adhesin
- important for adhesion and invasion of epithelial cells
- SPI4- mutant decreased in oral virulence in cows
What are the steps of invasion of epithelial cells from typhimurium?
- Adherence through SPI4 (SiiE)
- Invasion: SPI1 mediated translocation
Trigger or splash actin pol➡️membrane ruffling➡️invasion
How did they identify the genes involved in invasion in salmonella typhimurium?
Take virulent/invasive strain of bacteria➡️put genomic DNA onto plasmid➡️transform into non invasive strain➡️add gentamycin➡️plasmid with invasion genes survive cuz they go into cell. Those without invasion genes die from the antibiotics
When sequenced the genes involved in the invasion by typhimurium, what did they find?
Parts of SPI1! Included genes invABC
-invA- mutant: 50x higher LD50 for oral, same as WT for IP
