Pathogenicity Flashcards
what are virulence factors?
bacteria have them and they influence the ability to cause infectious disease
what are the two factors of virulence factors?
factors that promote bacterial colonisation of host
that damage the host e.g. exotoxins and endotoxins
6 points that virulence factors have which promote bacterial colonisation ;
adhere to host cells and resist physical removal invade host cells contact host cells resist phagocytosis evade immune defences compete for iron and other nutrients
name 3 ways in which the body defends against adhering bacteria
constant shedding of surface epethelial cells
removal of bacteria via coughing, sneezing etc
bacteria; removal by bodily fluids
what are the 3 mechanisms evolved by bacteria to avoid removal
pili
adhesions
capsules
what are pili?
a mechanism of adhesion
enables adhere to receptors on host cell= colonisation
what is the structure of pili?
thin protein tubes from cytoplasmic membrane and are found in all gram - bacteria
has a pilus
what is the structure of the pilus
shaft composed of a protein called pilim and at shaft is the adhesive tip structure - a protein celled lectin is present
what is lectin
protein found on end shaft of pilum and binds to specific glycoprotein or plycopolipid receptors on host cell
what are adhesion proteins
found in cell wall of bacteria
bind to specific receptor molecules on host cell
allow bacterium to adhere to cell and resist removal
what are capsules
produce a capsular polysaccharide matrix to form a biofilm on host tissue
what is a biofilm layer
found in capsules and consists of layers of bacteria adhering to host cells embedded in capsular mass
what protein allows invasion of host cells
invasin
what are invasins
proteins found in cell wall of bacteria -allow penetration
activate host cells cytoskeltal machinery leading to phagocytosis
3 ways bacteria benefit from being inside host cell
access to nutrient
protected from complement, antibodies etc
multiplies = disease
which bacteria colonise bladder and intestines and why
motile ones
with use of flagella to move
increases chances of reaching mucous for adhesion
2 points about capsules and how they resist phagocytic engulfment
capsules enable organisms to resist this
capsules interfere with bodys complement pathway
describe capsules and C3b
capsules can cover opsonin C3b bound to bacterial wall so that it cant bind to the C3b receptors on surface of phagocytes
4 ways in which bacteria resist phagocytic destruction
prevent acidification pf phagosome needed for effective killing of microbes using lysosomal enzymes
kill phagocytes by producing an exotoxin which damages the cytoplasmic membrane
are more resistant to toxic forms of oxygen and defensins
block vesicular transport machinery that enables phagosome to fuse tthe lysosome
4 ways bacteria can avoid immune defenses
change the adhesive tips
vary surface proteins so antibodies ‘dont fit’
have capsules made of acids present within host
produce protein A and protein g
describe protein a and g
both bind to Fc portion of antibodies that normally bind to Fc receptors on phagocytes
bacterium is then coated with protective coat of antibodies
what makes a bacterium pathogenic?
competition with host tissue and flora for limited nutrients
what are AB toxins
consist of two parts - active a component and binding b component
what is the b component of exotoxins
binds to receptor on surface of host cell
how does a component of exotoxins work
after b binds to host cell receptor a enters host cell by passing membrane- damage may be caused by adp-ribosylation of target host cell
what does the a component of AB toxins catalyse
ADP-ribosylation of host cell target proteins
how does NAD inactivate proteins
cleaved into ADPR which is covalently attached to host cell target protein causing inactivation
what is diptheria
common and leading cause of death in 1920s
immunisations carried out
what causes diptheria
produced by corynebacterium diptheriae
how doe diptheria cause disease
toxin interferes with host cell protein synthesis by catalysing the ADP ribosylation of host elongation factor 2(ef-2) necessary in order to tRNA to insert new amino acids into growing protein chain = cell death
what causes tetanus
produced by non-ribosylating bacterium
how does tetanus cause disease
neurotoxin binds to inhibitoru interneurons and blocks release of inhibitory molecules- cause contracted muscles to relax
how do inhibitory molecules allow muscles to relax
stop excitatory neurons from releasing acetylcholine
2 virulence factors that damage host
ability to produce harmful toxins
ability to produce cell wall components that bind host cells causing synthesis and secrete inflammatory cytokines
two points about Gram- cell walls
LPS (endotoxin) in outer membrane
it is because LPS is so immunogenic that it is toxis
two points about gram + cell walls
teichoic acid and peptidoglycan fragments
what are techoic acid composed of
polymers of glycerol, phiphates and sugar alcohol ribitol
2 harmful effects of bacterial cell wall components
minor infectin , few bacteria present
severe systemic infection
