Bacterial Host-pathogen Interaction Flashcards
What is infectivity
Ability to colonise and cause infection in host organism
What is pathogenicity
Ability to produce disease in a host organism
What is virulence
A term which refers to severity of disease
What is host-pathogen interaction
How pathogens (bacteria) sustain themselves and cause disease within host
Host pathogen interaction levels
Population
Individual
Cellular/molecular
Outcomes after pathogen exposure
- clearance of pathogen
- pathogen colonising / replicating in host
What influence whether or not pathogen will colonise in host
- co infection
- genetic factors
- hygiene
- occupational hazard
- pathogens ability to avoid immune detection
- pathogens ability to adhere to cells
- pathogens ability to avoid innate immune response
-pathogens ability to undergo stress
Does pathogen colonisation always lead to disease
No
2 main variables that influence outcome of exposure to a pathogen
- ability of pathogen to colonise and cause host damage
- immune status of host
What is commensal bacteria
Commensal bacteria are microorganisms that live in or on the body of a host organism without causing harm or disease.
Benefits of commensal bacteria
Protection against pathogens
Production of nutrients
Key abilities of pathogen
Transmit between hosts
Colonise host
Cause host damage
Direct contact
Skin-skin ~ Staphylococcus aureus
Sexual intercourse ~ Neisseria gonorrhoea
Indirect contact
Aerosol ~ Mycobacterium tuberculosis
Inanimate objects ~ Salmonella enterica, Vibrio cholerae
Vectors ~ Borellia burgdorferi
How are bacteria recognised by host innate immune system
PAMPS are recognised by PRRs!
Toll-like receptors (TLRs): TLRs are proteins that are expressed on the surface of immune cells and recognize specific molecules, such as bacterial lipopolysaccharides (LPS) and flagellin, which are associated with bacterial cell walls and flagella, respectively.
NOD-like receptors (NLRs): NLRs are intracellular receptors that recognize bacterial components, such as peptidoglycan and bacterial DNA, that are released into the host cell cytosol.
Complement system: The complement system is a group of proteins that can directly recognize and bind to bacterial surfaces, leading to the destruction of the bacteria by phagocytic cells.
Phagocytic cells: Phagocytic cells, such as macrophages and neutrophils, can recognize and engulf bacteria through various receptors, such as complement receptors and Fc receptors, which bind to antibodies that have been produced against the bacteria.
What are PAMPS
PAMPs, or pathogen-associated molecular patterns, are conserved molecular structures that are associated with pathogens
Examples of PAMPS
Peptidoglycan
Lipoproteins
DNA
Flagellin
Gram- only
Lipopolysaccharides
Gram+ only
Wall teichoic acids (WTA)
Lipoteichoic acid (LTA)
How are PAMPS recognised
PAMPs are recognized by pattern recognition receptors (PRRs) that are expressed on various immune cells, including macrophages, dendritic cells, and natural killer cells.
What are Pattern recognition receptors (PRRs)
Pattern recognition receptors (PRRs) are a family of proteins that are expressed by various cells of the innate immune system
When PRRs recognize PAMPs on the surface of pathogens, they activate downstream signaling pathways that lead to the production of cytokines, chemokines, and other molecules that recruit immune cells to the site of infection and activate them to eliminate the pathogen.
Different types of PRRs
Toll-like receptors (TLRs): TLRs are a family of transmembrane proteins that recognize a wide range of PAMPs, including bacterial lipopolysaccharides, flagellin, and viral nucleic acids. There are 10 different TLRs in humans, and they are expressed on various cell types, including immune cells, epithelial cells, and endothelial cells. Upon activation, TLRs trigger downstream signaling pathways that lead to the production of pro-inflammatory cytokines and chemokines, as well as the upregulation of co-stimulatory molecules on antigen-presenting cells.
NOD-like receptors (NLRs): NLRs are cytoplasmic receptors that recognize intracellular PAMPs, such as bacterial peptidoglycans and viral RNA. NLRs form inflammasomes, which are multi-protein complexes that activate caspases and lead to the secretion of pro-inflammatory cytokines, such as IL-1β and IL-18.
RIG-I-like receptors (RLRs): RLRs are cytoplasmic receptors that recognize viral RNA and trigger downstream signaling pathways that lead to the production of type I interferons (IFNs) and pro-inflammatory cytokines. RLRs are important for the detection of RNA viruses, such as influenza and hepatitis C.
C-type lectin receptors (CLRs): CLRs are a family of transmembrane receptors that recognize a wide range of PAMPs, including fungal cell wall components and viral glycoproteins. CLRs are expressed on dendritic cells, macrophages, and other immune cells, and they play a critical role in the recognition of fungi and viruses.
What do Toll like receptors recognise
recognise a wide range of PAMPs, including bacterial lipopolysaccharides, flagellin, and viral nucleic acids.
What do Nod like receptors recognise
recognise intracellular PAMPs, such as bacterial peptidoglycans and viral RNA
What do RIG-1 like receptors recognise
recognise viral RNA
What do C-type lectin receptors recognise
recognise a wide range of PAMPs, including fungal cell wall components and viral glycoproteins.
