Unit 1: Chapter 18 Microbial Pathogenesis Flashcards
Steps of Pathogenesis
- Entry
- Tissue Attachment and Colonization
- Immune Avoidance
- Host Damage
- Pathogen Exit
Pathogens are characterized by the presence of __________
virulence factors
Virulence Factors
Factors that may help pathogens cause disease in host
The more factors, the more dangerous the pathogen
Adhesion
Any microbial factor that promotes attachment
Different types of attachment
- Type I Pili/ Fimbriae
- Type IV Pili
- Cell Surface proteins
- Cell envelope components
- Capsule
- Teichoic Acid (gram positive)
- Components of Outer Membrane (o-polysaccaride can help attach)
Type I Pili/ Fimbriae
Static hairline appendages used only for attachment
The tip binds to a specific substrate on host tissue
Fimbriae and nonplus attachment proteins often collaborate to secure a pathogen to a host cell
Adhesion of type I Pili/Fimbriae
Step 1/ Initial Binding: Type I plus attaches to the host cell
Step 2/ Secondary (tighter) binding: Cell surface proteins and host cell receptors (integral)
Type IV Pili
Dynamic, thin, and flexible
Repeatedly extend and retract allowing “twitching” movement
Tight secondary binding is facilitated by other surface adhesions
Adhesion of type IV Pili
Step 1/ Initial Binding: Type IV pili attaches to cell surface and pulls it closer
Step 2/ Secondary (tighter) binding: Surface Adhesions
Bacteria can attach to surfaces in bulk, forming a _______
Biofilm
What is a biofilm?
A community of bacteria protected by an external called EPS that allows them to live in hostile environments. Formed in nutrient rich environments and will be flushed by water.
Can be made of anything (sugars, proteins, etc)
How is biofilm secreted?
By the bacteria
T or F: Biofilms are just single species
False
Biofilms can contain both single species or multispecies of bacteria
How do biofilms play an important role in chronic infections?
It helps enables persistent adherence and resistance to bacterial host defenses and antimicrobial agents
EPS protects the cell compared to the cells that may be outside the biofilm
T or F: Cell cannot dissolve the EPS and spread
False
They can dissolve the EPS and spread
Features of Exotoxins
- Gram negative and gram positive cells produce exotoxins
- Enzymes (proteins)
- Sensitive to heat
- Secreted by live bacteria
- Specific to their target cells (ex. neurotoxin)
Features of Endotoxins
- Only gram negative cells produce endotoxins
- Lipid A
- Heat- Resistant
- Released when bacteria dies
- Non- specific
___________ are part of the outer portion of the cell wall of gram negative bacteria
Endotoxins
Endotoxins are engulfed by macrophages which secrete ______
Cytokines
Endotoxins can cause
Very high fever, vasodilation, activate clotting factors, shock, and death if possible
What are the targets are bacterial exotoxins?
- Plasma membrane disruption
- Cytoskeleton alterations
- Protein synthesis disruption
- Cell cycle disruption
- Signal transduction disruption
- Cell-Cell adhesion disruption
- Vesicular trafficking
- Exocytosis
What can Staphylococcus alpha toxin cause?
Can cause lysis (bursting) of the host cell by disrupting the plasma membrane
How does Staphylococcus alpha toxin disrupt the plasma membrane?
By forming pores or breaking down membrane lipids
What are A-B Exotoxin’s
Intracellular Toxins
They bind to a receptor and enter a cell
Parts of A-B Exotoxin
B (Binding) region
A (Active) portion exerts effects inside
A-B Toxin Steps
- Bacterium produces and releases exotoxin
- B (binding) component of exotoxin attaches to host cell receptor
- A-B exotoxin enters host cell by receptor- mediated endocytosis
- A-B exotoxin enclosed in pinched-off portion of plasma membrane during pinocytosis
- A-B components of exotoxin separate.
- The A component alters cell function by inhibiting protein synthesis.
- The b- component is released from the hostel
What are two types of A-B Exotoxins?
- Diphtheria Toxin
- Cholera Toxin
What does diptheria toxin do?
It blocks ribosome function; cell dies
It creates toxin when there is decreasing amount of iron
What does cholera toxin affect?
It affects cell signaling inside the cell
How does cholera toxin affect cell signaling?
Luman has a channel called CTFA that opens when needed to let things in and closes when it doesn’t. Cl+ and Na+ is pumped when channel is open which makes the environment hypertonic and causes H2O to leave. ATP is used to make cAMP and adenylate cyclase helps make it but is not always active. Adenylate cyclase helps make it but is not always active and AC is made by a G-portion which is also not always active. This causes the channel to open.
Basically the G protein is in always on mode, so adenylate cyclase is being produced too much so Na, Cl, and water is being pushed out which leads to diarrhea
Is it more difficult to move toxins out a gram negative or gram positive cell?
A gram negative cell because toxins have to move out of 2 membranes (the outermembrane and the inner membrane)
Type II Secretion System
System that uses a pilus like structure as a piston to ram proteins through the outer membrane pore structure
Pushes protein out in piston manner from inner membrane to periplasm to outer membrane
What type of energy does type II secretion use?
ATP
Type III Secretion
Some microbes use tiny molecular syringes embedded in their membranes to inject proteins directly into the host cytoplasm
Basically sticks the protein directly into the host cell and goes into the cytoplasm of the host directly; no receptors are required so it makes it easy to infect
Type IV pili helps aid in _______
Pathogenesis
What type of bacteria is is there a wide range of type IV pili?
Gram Negative
Can biofilms live in in any surface, living or non living?
Yes they can live on both living and non living surfaces and the biofilm allows for them to live in hostile environments
What tissues do biofilms cause the most chronic infections?
Oral, lung, and urogenital
Type I Pili/Fimbriae E.coli Binding
Step 1/ Initial Binding: Attach to the host
Step 2/ Secondary Binding: Via cell surface proteins AND it injects the receptor into the cell
Tir proteins
Intimin proteins then attach
