Bacterial Pathogenesis Flashcards
(41 cards)
Every human is colonised,.
by numerous bacterium
A pathogen is
an organism that cause infection in individuals with normal host defences
A commensal is…
an organism that is found normally on those parts of the body that they are exposed to, or communicate with, the external environment
An opportunist is where
an organism that can cause infection in individuals with abnormal host defences
Koch’s postulates states….
- pathogen must be present in every case of disease
- Pathogen must be isolated from the diseased hose and grown in pure culture
- the specific disease must be reproduced when a pure culture of the pathogen is inoculated into a healthy host
- pathogen must be recoverable from the experimentally affected host
Disease can arise in several different ways…
- some bacteria are entirely adpated to the pathogenic way of life in humans. They are never part of the normal flora but may cause subclinical infection.
- Some bacteria which are part of the normal flora acquire extra virulence factors making them pathogenic
3.
Changes in normal flora
- changes in normal physiology and development
- when antibiotics select for a resistant flora
- new organisms may be acquired.
Pathogens can transmit via
oral-oral, fecal-oral, blood and sexual contact, Animals, vectors, environment and food
Microbial pathogenicity factors are…
examples of PAMP’s
bacteria need
cell wall associated proteins in order to bind to host cells
Gram positive proteins
have surface proteins which allow the attachment of the bacteria to the cell of the host
Gram negative bacteria use pili and fimbriae to
bind to host cells
Bacterial flagellae
confer motility to many bacteria and it is another example of a PAMP
Bacteria also needs to get something to eat
This occurs via the invasion of host cells. This is an example of a DAMP
Toxins produce different bacteria
- Exotoxins, which is any toxin that is actively secreted by a bacterium in the environment
- endotoxin (such as Lipopolysaccharides in gram negative bacteria)
- enterotoxin
Exotoxins can act like
proteases, .and other degrading enzymes
Type III secretion system
are needed for the delivery of toxins
for a bacteria to protect itself, it could…
make a polysaccharide capsule, slime, and biolfilm. LPS can be modulated by bacteria to cause cytokine overstimulation and lead to septic shock. Outer membrane proteins could affect antimicrobial peptides and complement factors
Bacterial adaptation is
adapting to changing and new environments
Microbe- host interactions include
- preventing opsonization
- toxin secretion can paralyze the host’s defences
- Disruption of mucosal integrity
- microbial recognition and host responses
- chemokine production
- inspired by modification of PAMP or interference with intracellular signalling or cell trafficking.
Regulatory networks include
Two component systems such as LPS modification, Quorum sensing, and Efflux pumps (drug resistance)
SIGNAL -
Environmental change - signalling molecule
Regulator
usually specific DNA binding protein - binds in control region
Regulon
Group of genes controlled by a common regulator
