Lecture 8-9 Gram negative bacteria (Part 2) Flashcards
Shigellosis is primarily a disease in what age group?
Children
Is the infectious dose of Shigella large or small and why?
Small. They are very acid resistant and are able to survive the stomach acid ‘sterilization process’.
What 2 main methods are used by Shigella to cause shigellosis?
- Infecting the mucosal epithelium of the colon by bacterial-directed endocytosis of M-cells (specialized phagocytic cells of the gut)
- They also can induce formation of actin-directed pseudopodia that thrust bacteria directly into adjacent mucosal epithelial cells without exposure to plasma proteins or phagocytic cells.
Is the infection local or systemic with Shigella?
Local. Local inflammatory ulceration of mucosal cells creates blood and pus in the stool. (dysentery)
What is the Shiga toxin?
An A-B toxin that cleaves ribosomal RNA, disrupting protein production in the cell.
What is the primary manifestation of Shiga toxin?
Damage to the intestinal epithelial cells.
What is Hemolytic Uremic Syndrome?
In a small number of patients (mainly young children), the shiga toxin gets into the blood stream in high enough concentration where it mediates damage primarily to the glomerular endothelial cells, resulting in renal failure. (Systemic)
What E. coli strain also contains a plasmid encoding a Shiga-like Toxin?
EHEC
Where does Shigella infect
Colon
Where does Salmonella infect?
The G.I. mucosa similar to Shigella
How does Salmonella typhi act?
It can break through the Gut epithelium and enter phagocytic cells which then act as Macrophage Taxis to take the pathogens throughout the body.
What the is the method by which enteric gram negative bacteria are spread throughout the body after inserting themselves inside the macrophage.
- They block lysosome fusion and multiply within the phagosome of machrophages
- Hitch a ride into draining lymph nodes, bloodstream, or other tissues (all while being protected from immune system)
- released upon the death of the macrophage causing bacteremia and infection.
Enteric Fever caused by bacteremia is also called what?
Typhoid Fever
Typhoid Mary was an example of what?
A permanent carrier of Typhoid fever
Most infections of Salmonella result from what?
Ingestion of contaminated food products
What age group does Salmonella infections affect?
All age groups
Is the infectious dose small or large for Salmonella and Why?
Large. Salmonella is very sensitive to stomach acid and requires a large does to become infected. This is contrary to Shigella
Is Salmonella infection local or systemic?
generally causes a localized infection of the small intestine mucosal epithelium.
How does the normal GI flora E. coli become pathogenic?
Genes that code for virulence factors can be transferred to non-pathogens including common GI normal flora such as E. Coli
Name the four pathogenic strains of E. coli
Enterotoxigenic E. Coli (ETEC)
Enterohemorrhagic E. coli (EHEC O157:H7)
Enteropathogenic E. coli (EPEC)
Enteroinvasive E. coli (EIEC)
2 characteristics of ETEC?
V. cholera exotoxin gene
Watery diarrhea
3 characteristics of EHEC?
Shiga-like exotoxin gene
Bloody dysentery
Hemolytic Uremic Syndrome (HUS)
3 characteristics of EPEC?
Shigella exotoxin gene
Adherence gene
Diarrhea
2 characteristics of EIEC?
Invasive genes
Dysentery
Most gram negative rods that produce UTIs originate where?
In the colon, contaminate the urethra and ascend into the bladder
UTI is an ____________ infection
Ascending
What is the most common cause of UTIs and why?
Uropathogenic strains of E. coli
They produce specialized adhesions that allow them to adhere within the urinary track.
What bacteria causes Plague rather than a GI infection in humans?
Yersinia pestis
Yersinia pestis causes a local or systemic infection?
Systemic with a high mortality rate.
What type of host are humans considered to be in Y. pestis infections
Accidental hosts. Infections are primarily Zoonotic
What are the typical hosts for Y. pestis
Rats, rodents and fleas
How is Y. pestis spread from a flea?
The bacteria replicate rapidly in the midgut of the flea. They eventually block the midgut and the next time the flea feeds it regurgitates into the fleabite.
What main exotoxin is used in Y. pestis
Superantigen
What is a necrotic bubo?
A dead lymph node which is a result of Y. pestis quickly replicating in a lymph node
What occurs with Y. pestis if the primary infection occurs in the lung?
Pneumonic plague
Immunity to cholera is a good example of what?
the value of maternal passive immunity
Is Vibrio Cholera resistant or sensitive to stomach acid?
Sensitive
Is Vibrio cholera invasive or non-invasive?
Non-invasive
What is the result of an infection of V. cholera?
A-B toxin enters the cells and activates adenylate cyclase, resulting in hypersecretion of water and electrolytes. Mortality rate falls from 60% in infants to 1% if promptly treated with replacement fluids and electrolytes
T or F, Antibiotics are secondary to fluids in a V. cholera infection/
True
What is the danger of synthetic infant milk formulas in some parts of the world?
In some communities sIgA immunity provided by mother’s milk is the only defense in babies against contaminated water and food. Synthetic infant milk formulas do not provide this protection.
Babies are most vulnerable to pathogens during what time?
During the “window of susceptibility”. This is a time when the maternal IgG is largely lost while the neonatal IgG levels are still low
