Mechanisms of bacterial infection Flashcards
Van Leuwenhoek
First described bacteria as animacules by looking at samples taken from his teeth under a microscope
Pasteur
Pasteurization (generation of bacteria), vaccine for anthrax
Koch
Created Kochs Postulates in order to identify bacteria. Discovered major bacteria like TB
Ehrlich
Introduced first antibiotic in 1910. Arsenic-based against Syphillis
Wacksman
Between 1940-1960 discovered most antibiotics used now.
Rise of Cellular Microbiology
In 70s/80s as antibiotic resistance went on rise. Bacteriology became important field once again
Phylotype
Study of bacteria, see if two species are related based on arbitrarily chosen level of similarity of gene marker.
Normally 97% similarity required. Most common gene marker is rRNA sequence.
Phylotype aka
Operational Taxonomic Units
Human bacterial diseases subdivide into 3 categories
Caused by
external environment
bacteria found in microflora
changes in host response to microbiota
Virulence
Relationship between organism’s virulence factors and ability to cause disease
Measuring virulence
Quantitively by
LD50
- lethal dose
- number of bacteria needed to cause death in 50% of population
IF50
- infectious dose
Steps of infection by exogenous pathogen
- Bind to host via adhesins
- Invade via invasin
- compete for nutrients
- grow to form biofilm and reach quorum sensing
- kill cells or take over their function to spread
- evade innate and adaptive immune system
- leave host and infect next one
how is iron found in the body
bound to proteins such as lactoferrin or transferrin
free-floating
surface virulence factors of bacteria
Flagella - long distance adhesin Pili and fimbriae - shorter and extend domain Bacterial capsule S-layer proteins Short fibrils
All these are examples of adhesins proteins
How to bacteria invade host?
Two mechanisms:
- Through gaps between epithelial cells
- Crossing though basement membrane
Role of invasins
Recognise surface carbohydrates on cells and cleaves proteins into peptides to allow invasion. Proteases.
How does bacteria take up iron
Free floating iron via high affinity siderophores
Protein bound iron by proteolysis of protein component
Role of protein toxins
Two roles:
Kill cells
Communication between the cells and bacteria. Bacteria take advantages of intracellular communication without the host cell being aware of what is happening.
Bacterial mechanisms by which they evade the immune system
Inhibit complement activation and activity
Developed proteins that bind to immunoglobulins
Developed proteins that degrade immunoglobulins
Developed superantigens inhibiting B cell function by causing massive non-specific activation of B and T cells which leads to wasted effort
Antigenic variation
Inhibits phagocyte killing by developing capsule or via intracellular inhibition
Developed superantigens that kill or inactivate large numbers of T cells
Developed bacterial proteases that degrade cytokines and antimicrobial peptides
Biofilm formation
Role of biofilm
Biofilm is formed by bacteria surrounded by matrix. this matrix allows the bacteria to avoid contact from the immune cells and complement system (prevents opsonization)
What is quorum sensing?
Way in which the bacteria communicate.
Produce autoinducers - let bacteria sense the population density.
When there are few cells in the area - little autoinducers made will diffuse into the environment and the levels of autoinducers that travel into the cell will remain low.
When more bacteria are present - autoinducer concentration will increase as more bacteria are producing them.
When autoinducer concentration gets high enough indicating a critical density of bacteria, autoinducers will bind and activate receptor proteins inside the cells
This protein acts as a transcription factor
What type of proteins are adhesins?
High affinity proteins
