Bacterial Pathogenesis Flashcards
Are all bacteria pathogens?
No, most bacterial species are commensal flora mostly harmless or even beneficial to the host however, there are some pathogenic bacteria including these commensal flora when presented with optimal conditions to exhibit pathogenic effects
Define Pathogenicity
The ability of an infectious agent to cause disease
Define Virulence
The measure of ability to cause disease
Define Pathogenesis
The process of disease progression
Define Commensal
A microorganism which naturally resides harmlessly on the body in balance with the host’s immune system
Define Oppurtunistic Pathogen
A pathogen only able of causing disease when allowed to do so through particular circumstances of the host
Define Nosocomial Infection
Healthcare-associated infection
What are the 5-steps of pathogenicity?
- Gain access to the host
- Bacterial adhesion
- Aqusition of nutrients
- Evading host defences
- Damaging the host
Enodgenous versus Exogenous
How does bacteria gain access to the host?
Endogenous infections are caused by commensal bacteria becoming oppurtunistic pathogens
Exogenous infections are aquired from an external source in the environment or from another animal
How do bacteria adhere to host?
Most bacteria (harmless bacteria) removed via natural flushing action of body fluids and muco-ciliary escalator
Pathogens resist this flushing via proteins called fimbriae, strands that extend out of the bacterial cell and adhere to specific cells of the host
How do bacteria aquire nutrients within their host?
- Pathogenic bacteria need nutrients in order to replicate and multiply
- Amino acids and sugars are readily available
- However, body contains tiny amount of free Fe3+ ions
How are pathogens adapted to aquire iron?
Not a lot of free Fe3+ but, lots bound to other molecules such as haemoglobin, transferrin, lactoferrin etc. therefore, iron can be scavenged or harvested from sources in the body by proteins produced by pathogens such as siderophores which mop up free Fe3+
How do pathogens evade host defences?
- Evade phagocytosis as they have capsule or LPS which are hydrophilic and means the bacteria is unable to be detected by phagocytic cells
- Some bacteria produce capsule or LPS that is no-stabilisng for complement meaning opsonophagocytosis cannot occur
- Some bacteria avoid provoking antibody production by molecular mimicry - antibody not produced = bacteria persists
- Some bacteria can hide inside of cells e.g. Obligate intracellular pathogens (can only replicate inside cells) or Faculative intracellular pathogens (replicate in and out of cells)
How are some pathogenic bacteria adapted to grow inside host cells?
- Inhibit phagosome/lysosome fusion
- Lyse phagosomal membrane and escape into the cytoplasm
- Resist killing mechanisms
How do pathogenic bacteria damage their hosts?
Production of exo- or endotoxins
or
Immune-mediated injury
