04 Bacterial Pathogenesis Flashcards
Adherence to host surfaces
Adherence to host surfaces*
- Prevents bacteria from being carried away by mucus or washed swept away by fluids
Pili/fimbriae
- Neisseria gonorrheae and E.coli adhere to urethral mucosa
- Teichoic acids
- main function of teichoic acids is to provide rigidity to the cell-wall by attracting cations such as magnesium and sodium
- Adhesins (appendages of bacteria)
- Slime layer (glycocalyx)
- Capsular material of Staph epidermidis allows it to attach to prosthetic devices and form a biofilm
Antiphagocytic surface factors*
Antiphagocytic surface factors*
Ways bacteria escape phagocytosis:
- Antiphagocytic surface factors*
- via their Capsules
- via cell wall proteins
- IgA proteases
Antiphagocytic surface factors
Antiphagocytic surface factors
(way bacteria uses to evade phagocytosis)
- Capsules – allow the bacteria to escape phagocytosis until they become opsonized (coated by antibodies)
- Cell wall proteins of some bacteria
- M protein of Streptococcus pyogenes
- Protein A of Staphylococcus aureus
IgA proteases
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IgA proteases
(way bacteria uses to evade phagocytosis)
- Breakdown IgA immunoglobulin present on mucosal surfaces
- 3 agents causing meningitis, all are encapsulated and produce IgA proteases
- Neisseria meningitidis*
- Haemophilus influenzae type b*
- Streptococcus pneumoniae*
invasion methods of bacteria
invasion methods of bacteria
Several enzymes secreted by bacteria play a role in invasion:
- Collagenase and hyaluronidase
- Degrade collagen and hyaluronic acid allowing spread
- Coagulase
- Eg. Produced by Staph aureus, enhances clot formation and walls off bacteria from phagocytic host cells
- IgA protease
- Leukocidins
- Which can destroy neutrophils and macrophages
What is Coagulase? Give me an example.
Coagulase
- Eg. Produced by Staph aureus, enhances clot formation and walls off bacteria from phagocytic host cells
Mechanisms for escaping Host Defenses using Capsule. Give an example bacteria.
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Mechanisms for escaping Host Defenses
Capsule *
- Help evade phagocytosis
- Protects from destruction within phagolysosome of macrophage or leukocyte
- Hyaluronic acid capsule of Strep. pyogenes
- Mimics human connective tissue – masks the bacteria
- Biofilm production
- Adherence to structures eg. Slime of Staph epidermidis helps it to infect prosthetic devises
Mechanisms for escaping host defenses via Antigenic variation. name example for each
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Mechanisms for escaping host defenses via Antigenic variation
Antigenic variation *
- Eg. Neisseria gonorrhoeae
- Varies the structure of the pili on it’s surface thereby evading the immune system
Inactivation of complement components
- Eg. Strep pyogenes degrades complement C5a
- Limits chemotaxis of neutrophils to site of infection
What iron binding compounds do some bacteria produce?
Bacteria produce iron-binding compounds Siderophores that compete for iron*
- Capture iron from the host by chelation
- Ferrated siderophore binds receptors on bacterial surface
- Iron is actively transported into the bacterial cell
- (Exception – Pathogenic Neisseria species
- Do not produce siderophores
- Utilize host-binding proteins (transferrin, lactoferrin) as iron sources
- Possess dedicated receptors that bind these host proteins and remove the iron for internalization)
Exotoxins Polypeptides characteristic
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Exotoxins Polypeptide characteric
**Polypeptides **
- Genes coding for toxins usually located on plasmids
- Some toxin genes are carried and transmitted by bacteriophages (viruses that infect bacteria)
- Egs. Diphtheria toxin, cholera toxin, botulinum toxin
Note:
List of exotoxin characteristics:
- Polypeptides
- Antigenic
- Can be converted to Toxoids
- A-B subunit toxins
Exotoxins are produced by many bacteria (gram+ and gram-)
exotoxins are secreted into the surrounding environment.
exotoxins antigen characteristic
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Exotoxins antigen characteric: Antigenic
Most are Antigenic*
- stimulate the formation of specific antibodies
- These specific antibodies can bind and neutralize toxin – are called “Antitoxins”
Note:
List of exotoxin characteristics:
- **Polypeptides **
- **Antigenic **
- **Can be converted to Toxoids **
- A-B subunit toxins
Exotoxins are produced by many bacteria (gram+ and gram-)
exotoxins are secreted into the surrounding environment.
exotoxins toxoids characteristic
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exotoxins toxoids characteristic
exotoxins can be made into Toxoids*
-Subjecting exotoxins to **low **heat and chemicals (eg. Formaldehyde) in the laboratory environment inactivates them
-Lose toxicity (cannot cause host tissue damage)
-Retain antigenicity
- Can still stimulate the immune system to produce antibodies
- Therefore Toxoids are used in some vaccines*
- *-Egs. Tetanus toxoid, diphtheria vaccine**
Note: List of exotoxin characteristics:
Polypeptides
Antigenic
Can be converted to Toxoids
A-B subunit toxins
Exotoxins are produced by many bacteria (gram+ and gram-)
exotoxins are secreted into the surrounding environment.
Exotoxins A-B subunit characteristic
Exotoxins A-B subunit characteristic
- Most have A-B subunit* structure (dimeric)
- B (binding) subunit binds the exotoxin to specific receptors on target cells
- A (active) subunit enters the host cell and exerts it’s effect
- 2 examples of A-B subunit toxins:
- Diphtheria toxin – inhibits protein synthesis
- Cholera toxin – activates cAMP
Note: List of exotoxin characteristics:
- Polypeptides
- Antigenic
- Can be converted to Toxoids
- A-B subunit toxins
Exotoxins are produced by many bacteria (gram+ and gram-)
exotoxins are secreted into the surrounding environment.
Cholera toxin*
Cholera toxin*
Cholera toxin is an example of A-B subunit toxins:
- B subunit binds to ganglioside GM1 receptors on intestinal epithelial cells
- A subunit is internalized
- Causes ADP-ribosylation of G-protein
- Activates Adenylate cyclase *
- Increase in cyclic AMP (cAMP) *
- Hypersecretion
- Loss of water and ions
- Diarrhea
Note: List of exotoxin characteristics:
Polypeptides
Antigenic
Can be converted to Toxoids
A-B subunit toxins
Exotoxins are produced by many bacteria (gram+ and gram-)
exotoxins are secreted into the surrounding environment.
