Reed Lectures Flashcards
2 properties of a bacterial pathogen
- can colonize host
- causes disease
Many bacteria in the environment don’t cause disease
Not all strains of a pathogen will cause disease
Define virulence. Give a major determining factor for virulence
Ability to cause disease; host susceptibility
Define virulence factor, and give an example
Any strategy that promotes disease-causing properties/causes virulence
ex. toxins, secretion systems
T or F: infection always leads to disease
False. Asymptomatic ppl are called carriers (colonized by bacteria, but show no symptoms of disease)
Define bacterial pathogenesis
Mechanisms through which bacteria cause disease
Why is it important to study bac path?
To development prevention strategies (Vaccines) and treatments (Antibiotics)
3 bacteria that Robert Koch studied
B. anthracis
M. tuberculosis
V. cholerae
List Koch’s postulates
- Microbe must be associated with symptoms of disease and must be present at site of infection
- Microbe must be isolated from disease lesions and be grown in pure culture
- Inoculation of isolated bacteria into healthy host needs to generate the same disease
- The same microbe must be re-isolated from the inoculated host
Give limitations to Koch’s postulations
- Not all infections lead to clinical symptoms; host susceptibility determines virulence and whether disease develops or not
- Cannot grow many bacteria in pure culture due to complex nutritional/environmental needs for growth
- To test the 3rd postulate, you need a perfect animal model that perfectly replicates the disease seen in humans. Often, this is not the case. The strain of bacteria causing disease X in humans may not cause the same symptoms in mice. Therefore, may need to change the mouse (ex. mutant mice), or use another strain of bacteria to emulate similar symptoms
Give 2 molecular biology techniques that can be used to identify presence of microbes in carriers
- PCR - identifies bacterial DNA
2. IHC - identifies bacterial proteins
Who developed the molecular Koch postulates?
Stanley Falkow
List the molecular Koch postulates
- A suspected virulence factor (gene) should not be present in the avirulent strain.
- Disrupting the virulent gene should attenuate its virulence. Reintroducing WT gene should reconstitute virulence
- Putting putative virulent gene in non-virulent bacteria should cause it to become virulent
Give limitations to the molecular Koch postulates
- virulence may be multifactorial - requires multiple genes/a gene cassette for full virulence to occur
- disrupting bacterial metabolism/biochemical pathways can also attenuate virulence - are such housekeeping pathways virulence factors?
uropathogenic E. coli (UPEC) causes what infection?
UTI (urinary tract infection)
What cell type does UPEC infect?
bladder epithelium
Give 4 ways that UPEC can interact with host cells
- Attachment via pili
- rearrange host cell cytoskeleton by interacting with actin
- interact with host signalling pathways
- form microcolonies
T or F: coordinated expression of virulence facts is essential for full virulence and disease
T
UPEC expresses Type __ pili. It is required for what?
Type 1. Needed for colonization, invasion, persistence.
Where do IBCs form? nucleus, vesicles, or cytoplasm?
cytoplasm
What are IBCs
Intracellular bacterial colonies
Are filamentous bacterial cells (UPEC) proliferating or non-proliferating?
Proliferating - allows them to evade killing by neutrophils
What are quiescent intracellular reservoirs? (QIR) What type of host cell are they established in?
Non-replicating bacteria form QIR for long term survival. Established in transitional cells below uroepithelium.
Name 1 toxin that UPEC secretes for nutrient acquisition
alpha-haemosylin (HlyA) - lyses host cell to release nutrients
Also a way for UPEC to exit 1 cell and spread to another
T or F: UPEC doesn’t need coordinated expression of virulence factors to cause disease
F - expression of proteins/virulence factors needed to cause disease are organized into 3 main steps: entry, survival + proliferation in cell, exit.
T or F: Knocking out 1 virulence factor may lead to avirulence, but it may still lead to full disease
F - full disease requires combined effects of each virulence factor. Ability for bacteria to cause disease may be attenuated if one virulence factor is missing/mutated/disrupted
Is a single virulence factor known to be essential for virulence sufficient to cause full disease?
NO. Full disease requires combined effects of each virulence factor
T or F: Sec and Tat secretion pathways are present in Gram negatives only
F. they are common to both Gram + and -
What does Tat stand for?
Twin arginine translocation
What are the Sec and Tat pathways?
General bacterial secretion pathways used to transport proteins across cytoplasmic membrane.
T or F: many proteins are secreted through the Sec and Tat pathways
T
T or F: many proteins secreted by Sec and Tat systems are secreted outside the cell
F. Most proteins secreted through these systems are destined for periplasm or cytoplasmic membrane
The _____ is required for proteins to be localized to a specific location
signal sequence
T or F: 2 step pathways are commonly required in Gram + bacteria to secrete proteins out of the cell
F. commonly required in Gram NEGATIVE bacteria. The first step often involves Sec or Tat, while the second step (secretion out of cell) involves another secretion system
Are Sec and Tat pathways active or passive transport systems?
Active
The general Sec pathway transports folded or unfolded proteins?
unfolded
The protein transported by Sec pathway often have a signal sequence at C or N terminal?
N
T or F: The general Sec pathway is not essential to gram + and - bacteria.
F - ESSENTIAL for survival bc most proteins are transported through this pathway
What provides the energy for active transport in Sec pathway?
SecA - an ATPase, and proton motive force
T or F: Tat pathway is a passive transport system.
F - ACTIVE
Tat pathway transports unfolded or fully folded proteins?
Fully folded; bound to cofactors
T or F: Tat pathway is present in all bacteria
F
Proteins that go through Tat pathway must have what signal?
twin-arginine motif on N terminus
T or F: Many proteins that enter general Sec pathway are bound to cofactors
F - many proteins entering TAT pathway are bound to cofactors
Energy to transport proteins in Tat pathway comes from where?
Proton motive force
List 4 Gram + secretion systems
General Sec Pathway (essential)
Injectosome
Sortase system (SrtA)
T7SS/ESX
The sortase system anchors proteins to the ___ of Gram+ bacteria
cell wall/precursor peptidoglycan
The sortase systems recognizes proteins coming through the ___ pathway with a ____ motif
Sec; LPxTG
T or F: The LPxTG motif is present at the N terminus of the protein.
F - present at C terminus. The N terminus contains the signal sequence
Which Gram + secretion system transports small proteins ~100 AA long?
T7SS/ESX
Which Gram + secretion systems transports proteins with WxG motif?
T7SS/ESX
T or F: T7SS-exported proteins often dimerize
T
Give a major pathogen that contain the T7SS
M. tuberculosis
Is the Sortase system in Gram + or -?
+
Is the ESX system in Gram + or -?
+
T or F: injectosome transports things across cell wall directly into host cell cytoplasm
T
T or F: T7SS forms a channel.
T
Give the functions of ESX-1, ESX-3, ESX-5
ESX1; pokes holes in phagosomes to transport bacterial proteins into cytoplasm; essential for bacterial survival in phagosomes
ESX3: Fe acquisition
ESX5: involved in host immune invasion; secretes mycobacteria specific PE and PPE protein families
Define exoproteins/exotoxins
Proteins secreted outside the bacterium and acts on host cell
Define effector proteins
Bacterial proteins secreted directly into host cell cytoplasm ; mediated by T3, 4, and 6 SS
T or F: Effector protein secretion is dependent on Sec pathway
F: independent
Are all Gram - secretion systems essential?
No - this makes them good targets for antibiotics bc they’re not under pressure to mutate to survive the drug
Flagella is used in which types of bacterial motility?
Swarming and swimming
What is a peritrichous bacterium?
Bacterium with several flagella all over its body
T or F: The flagella is a simple structure
F
T or F: All genes involved in structure, regulation, and function of flagella are considered virulence factors
T
T or F: T5SS are thought to have evolved from flagellar systems
F: T3SS
Motile bacterial cells run or tumble more frequently when they are moving towards chemoattractants?
Run
T or F: flagella expression can be regulated
T. Also, flagella can switch from polar states to peritrichous states.
Primary lesions are associated with latent or active TB?
Latent
The greatest number of Mtb bacteria are found in which structure? Why?
Cavitary lesions; lots of oxygen
List the main factor that induces Mtb dormancy in latent TB:
Availability of oxygen
Granulomas contains lots/little oxygen? What is the word for lacking oxygen?
Very little; granulomas are hypoxic