Pathogenicity: adhesion, colonisation and toxins Flashcards
What needs to be present for a disease to occur?
a microorganism/ a number of bacteria to need body/ the quality of a persons specific and non-specific body defences
What are the 2 categories of virulence factors?
- virulence factors that promote bacterial colonisation of the host
- virulence factors that damage the host - ectotoxins and endotoxins
What are the 6 virulence factors?
- adhere to host cells and resist physical removal - stick
- invade host cells - invade
- contact host cells - contact
- resist phagocytosis
- evade immune defences
- compete for iron and other nutrient
true or false dies the body have an innate ability to remove bacteria?
true
What are some of theses defences
- shedding of surface epithelial cells from the skin and mucous membrane - skin shedding
- coughing, sneezing, vomiting, diarrhoea
- body fluids like saliva blood mucous and urine
What are pili?
thin protein tubes that come out of the cytoplasmic membrane - almost all gram negative bacteria but not many gram positive bacteria
What do pili let the bacteria do?
adhere to reception on target host cell and colonise and resist flushing
Structure of a pili
shaft made up of protein pilin
at the end there is an adhesive tip which is a protein called lectin which can bind to glycoprotein to fly-lipid receptors on the host cell
can pili switch adhesive tips?
Yes - allows them to collate different cell types and so evade antibodies
What are adhesins?
proteins in the cell wall of bacteria that bind to receptor molecules on the surface of host cells
they allow bacteria to adhere imtinamly to the cell
What are capsules?
capsular polysaccharide matrix forms a biofilm on host tissue - layers of bacteria adhering to host cells and embedding in a capsular mass
What is invasin?
proteins found in the cell wall of various bacteria that allow bacteria to penetrate host cells
What can invasins do?
active the host cells cytoskeletal machinery enabling bacterial entry into the cell by phagocytosis - engulfment
Why does it help the bacteria to the motile - be able to move
better chance of making contact with mucous memebrane in intestines - they can move through the mucous to place les viscous
what do capsule allow bacteria to resist
phagocytic engulfment
What does IgG do
stick antigens like bacterial proteins to phagocytes
structure of an IgG molecule
tip (Fab) has a shape that fits bacterial antigen
stalk (Fc) bind to receptors on the phagocytes
What is C3b?
a protein which binds to bacterial surface proteins and C3b receptors on phagocytes once the coplesmen defence pathways are activated
What are C3b and IgG called?
opsonins
what are ways that bacteria can resist phagocytic destruction?
they prevent the acidification of the phagosomes which is needed for effective killing of microbes by lysosomal enzymes
- can kill phagocytes by producing exotoxin leukocidin
- more resistance to toxic forms of oxygen and to defensins
- block vesicular transport machinery that enables the phages to fuse with the lysome
How can bacterial evade immune defenses?
change surface proteins so that the antibodies no longer fit
What does bacteria need to do be pathogenic?
compete successfully with host tissue and normal flora for limited nutrients
what are the 2 types of virulence factors
- ones that promote bacterial colonisation
- ones that damage the host
Structure of A-B toxins
B (binding) component which binds to receipt on surface of susceptible host cell
A (active) component which enters host cells start the ADP-ribosylation of target host cell protein
