Bacterial Pathogenesis Lecture 9-11 Flashcards
What is a selective medium?
Selects for growth of a desired organism, stopping the growth of or altogether killing non-desired organisms
What is a differential medium?
Contains compounds that allow groups of microorganisms to be visually distinguish between groups of bacteria (becuase they look different)
In order to isolate bacteria that is not responding to antibiotics (penicillin and erythromycin) but is susceptible to ciprofloxacin- what growth conditions should you use?
Erythromycin and penicillin
How can you prevent a cholera outbreak?
- Vaccine (toxoid vaccine or a live attenuated vaccine) for localized immunity
- travel safe: clean drinking water, food and hygiene
What are the virulence factors for V.Cholerae?
Cholera Toxin (CT), and toxin-coregulated pili (TCP)
What is TCP?
Adhesion needed to colonize the small intestine
What is CT?
- enterotoxin
- B subunit binds to a structure on the host cell
- A subunit: delivers toxic enzyme
How does CT enter the host cell?
- Endocytosis, then the vesicle transports to golgi, then ER
- A subunit activates G protein, which activates adenylate Cyclase
- cAMP opens the ATP-gated anion channel
How does the CT-A subunit interrupt the normal GPCR-G pathway?
- adds ADP to the G alpha subunit so it cannot associate with GCPR
- this causes ADP to bind to AC and leads to Cl- secretion (cAMP, then PKA)
How does CT lead to electrolyte imbalance? How does water get drawn into the lumen of the intestine?
- Cl is secreted from the cell into the lumen of the intestine, so Na+ cannot be absorbed by the cell
- there is a higher concentration of Na+ and Cl- in the intestine, and this draws water out due to osmotic imbalance
How can you get immunity to ETEC?
Dukarol vaccine: provides immunity to the heat-labile toxin of ETEC
Why does the ETEC vaccine have inactivated forms of cholera and not E. Coli?
The heat labeled toxin (LT), has the same 3D structure, receptor and mechanism of action as cholera, so antibodies for cholera bind to ETEC LT toxin and neutralize it
Why are secretion systems essential?
- provides movement across the bacterial cell envelope
- attaches to surfaces and transfers DNA
- does specialized functions in pathogens
How are secretion systems classified?
- transported effector molecules
- targets
- producing cell type
Which types of bacteria contain Sec, Tat and T4SS?
Both gram neg and positive
Which secretion systems have been identified in gram neg bacteria?
T1SS, T2SS, T3SS, T5SS, T6SS
What is the type of secretion system that is found in both cell types?
T4SS
What is the difference between a facultative and obligate intracellular pathogen?
Facultative: can live outside or inside the pathogen
Obligate: must live within host cells
What are the advantages to being an intracellular pathogen?
- access to nutrients
- osmotically balanced environment
- protection from immune system
- protection from antibiotics that don’t go through the cell membrane
What virulence factors do intracellular bacteria need?
- something that allows entry into the cell
- something that allows their survival once inside
What is an invasin?
A protein that allows entry into the host cell
Why are injectisomes advantageous?
- protein effector is not diluted into the environment
- the protein effector can act on internal host cell structures
What is a pathogenicity island?
- Genetic elements that are acquired by horizontal gene transfer
- encode virulence factors and are normally absent from non-pathogenic strains
What is the structure of a T3SS?
- translocation pore, needle, basal body
What are the two types of salmonella?
S. Typhi (blood), and S. typhimurium (GI tract)
How do you treat the two types of salmonella?
Typhi: antibiotics
Typhimurium: rehydration therapy
What is involved in the pathogenesis of salmonella infections?
Two SPIs:
SPI-1-encodes a T3SS that is needed for cell invasion
SPI-2: needed for intracellular survival inside the host cells
What does SPI-1 do?
Injectisome for internalization of bacterium: injects invasin proteins into intestinal epithelial cells, which triggers actin rearrangements inside the host cell— causes membrane ruffling and formation of pseudopods that engulf the bacterium and internalize it inside the vacuole
What is SPI-2?
- Injectisome for replication inside vacuole; injects effector proteins into cytoplasm/endomembrane system
- effector proteins modify the vacuole membrane and maintain it so the bacteria can reproduce (otherwise would be killed)
- it also stops lysosome/phagosome fusion and killing
