Biochemistry - Pathogenesis and Virulence Flashcards
What two factors can describe pathogens?
Pathogenicity
Virulence
Pathogenicity
The ability to cause disease.
Virulence
The degree/intensity of pathogenicity
Infection
This refers to persistence of bacteria, not necessarily meaning tissue damage.
Disease
Cause overt damage to the host, where body parts cannot fulfill normal function.
Kochs Postulates
These are a set of criteria used to establish relationship between micro-organisms and disease.
When were Koch’s Posutlates proposed?
By Robert Kock in late 19th century.
What is the first Koch Postulate?
Micro-organism msut be present in all cases of the disease, isolated and identified in every individual with it.
What is the second Koch Postulate?
Isolation from the host and grown in pure culture, for identification of cause-and-effect relationship between organism and disease.
What is the third Koch Postulate?
Must cause the same disease when inoculated into a healthy hot.
What is the fourth Koch postulate?
Re-isolation from inoculated, diseased host and identifed as being identical to the original microorganism
What diseases were discovered using Kochs Postulates?
Anthrax, TB and Cholera
What is the basis of Koch’s Postulates?
This is taking of an animal, isolating microorganisms from the diseases then re-injecting into lab animal.
What are the two types of Pathogen?
Oppurtunisitc
Primary(Obligatory
Oppurtunisitc Pathogen
These are microbes causing disease in immunocompromised hosts, less so in healthy patients.
Obligatory Pathogens
These can cause disease in absence of immune defects, needing disease to survive.
What are the stages of infection for pathogens?
Emerge from Reservoir
Transport To Host
Adherrence/Colonisation
Tissue Invasion
How may host transport be facilitated?
Direct like sneezing, airborne, body contact.
Indirect like vectors(Zoonosis) or arthropods, vehicles, food, water, soil etc.
What are the requirements of adherence?
Adhesins
Host Cell-Receptors
Biofilm FormatioN
Adhesins
These are virulence factors allowing bacteria to attach to host cells
What is the structure of Adhesin?
Extension from pili, fimbriae, flagella.
What are examples of host cell receptors?
Integrins, Cadherins or Glycosaminoglycans.
Why might biofilm formation be important?
Body has mechanisms to remove bacteria
Extracellular Polymeric Substnaces
This is an adhesive matrix anchoring bacteria into place, regulated by quorum sensing for co-ordinated behaviour
What is an example of host recogntion?
Streptococcus binding salivary glycoproteins and hydroxyapatite, adherring to teeth.
How might pathogens have to compete with microflora?
Nutrient acquistions, toxin production, biofilm formation and immune evasion.
What is the process of adherrence?
Non-specific forces like charge/hydrophobicity, then specific bacterial adhesins and host receptors.
How do non-specific interactions faciliaate bacterial binding?
Net surface charge of bacteria is negative due to LPS and teichoic acids
What is an example of invasion?
E.coli strands binding urinary tract cells by pili and adhesin production through chaperone-usher pathway, guiding pilin assembly of subunits into a filamentous structre.
How might strains bind Brush Border Villi?
Capsules and decay-acceleration factor on intestinal epithelial cells.
Biofilm
This is the secretion of a matrix of extracellular polymeric substances assisting in 3D community development to protect bacterial from external stressors.
What is EPS secretion of biofilms facilitated by?
Genes and environmental cues, like quorum sensing.
What are examples of adhesins specific to host receptors?
Fimbriae and Pili, Capsules, S-Layers, Flagella or Teichoic acids.
Siderophores
These are small, high-affinity, iron-binding molecules chelating iron from host proteins and transporting it into bacterial cells.
How is siderophore protein production regulated?
Transcriptional regulators that respond to envrionmental iron levels
Transferrins
This is a blood plasma binding and transporting iron throughout the body, synthesised and secreted by the liver.
What is an example of a siderophore?
Sigma Factor PVDS regulating pyoverdine production in P.aeruginosa in response to low iron.
What are the barriers to bacterial infection?
Lysozymes in tears
Skin
Mucus in lungs
Cilia in respiratory systems
Flora competition
How do lyzozymes work?
Cleavage of the glycosidic bond connecting PG in the bacteria cell wall leading to lysis.
How does the mucus prevent infection?
Complex network by goblet cells of mucin cross-linking being gel likes
What are examples of tissue invasion?
Pentration or between cells
Phagocytic cell invasion
Adhesin interaction
How can bacteria invade phagocytic cells?
Adhesin interaction to neutrophil/macrophage with phagocytosis engulfment or injection of effector proteins into host cell to prevent phagosome maturation.
How can lytic compounds be used for invasion?
Killing of cells, lysing area of invasion
What lysing compounds are used?
Collagenase, Phospholipase and Hemolysins
Hemolysis
This is the destruction of RBC.
How might bacteria evade host immune response?
Bypassing IIR like phagocytic cells, complemenet system, cytokines or chemokines
AIR avoiding antibodies and T Cells.
How can avoidance occur?
Prevent macrophage capture
Antibodiy production
How do antibodies work as ah ost defence?
Produced by B-Cells, surrounding a microbe to prevent its attachment.
What is an example of a bacteria colonising wounds?
Clostridium perfringens producing gangrene
