lecture 33 Flashcards
what does pathogenicity mean
the ability for something to cause disease
what are the Koch’s postulates
guidelines that are used to demonstrate that a specific pathogen causes specific symptoms of disease
what are the exceptions to Kochs postulates
the fact that not all microbes can be cultured and re-inserted into an organism and the fact that pathogenic bacteria can be found in healthy people.
what does the finding of pathogenic bacteria in healthy people imply
it implies certain strains of disease causing microbes have specific virulence factors that aren’t present in all bacterial strains
what are the key stages of pathogenesis
1: the microbe must adhere to host cells
2: the microbe must invade the host tissue
3: the microbe will then replicate in the tissue and colonise it
4: when the population is large enough, the population is able to cause disease. this can be done by toxins or by direct tissue damage.
what virulence factors help with step one of pathogenicity
the many tiny fimbriae on the membrane of the bacteria.
what does fimbriae specificity mean
it means that the bacteria will only bind to specific cell tissues.
whats an example of bacteria with fimbriae virulence factor
Neisseria gonorrhoeae
what virulence factor is associated with stage 2 of pathogenicity
one factor helping this is the flagella. There are also internalin related proteins, these proteins are used to get into the tissue
how does flagella aid the host tissue invasion
it helps the bacterias motility through mucus of tissue
what virulence factors help step 3
associated virulence factor could be the capsules Another virulence factor that aids this stage are siderophores,
how does the capsule virulence factor aid pathogenicity
it prevents the bacteria from being phagocytosed
how do the siderophores aid the pathogenicity
one example of siderophores Yersinia bactin solubilises metal bound to host proteins and transports it to the bacteria
whats an example of a siderophore
Yersiniabactin
what virulence factors help in stage 4
endotoxins and exotoxins
what are endotoxins
things like the lipopolysaccharide on the bacteria or proteins from the membrane. components of the gram negative bacteria
what bacteria type do endotoxins come from
gram-negative
how do endotoxins work
they are apart of the normal bacteria, but when the bacteria dies and degrades these toxins cause a very strong immune response, so they cause innflamation
describe exotoxins and their three sub catagories
toxins that are produced within the bacteria then released. can come in the form of cytotoxins, neurotoxins and enterotoxins.
whats an cytotoxin
a substance (such as a toxin or antibody) having a toxic effect on cells.
whats a neurotoxin
a poison which acts on the nervous system.
whats an enterotoxin
a toxin produced in or affecting the intestines,
whats an example of a cytotoxin and how does it work
Streptolysin which is secreted by Streptococcus pyogenes and causes beta Haemolysis of red blood cells
what are the three types of Haemolysis and whats the odd one out
alpha, beta and gamma. gamma is odd one out as its actually no haemolysis
whats an example of a neurotoxin and what does it do
n example of this is (Botulinum) produced by the bacteria Clostridium botulinum, this causes paralysis of muscles.
how does a neurotoxin work
It interferes with muscles workability. At the NMJ synapse botulinum stops the binding of ACh vesicles to the axon terminal, so no ACh is released across the synaptic cleft.
whats an example of an enterotoxin
these are associated with dysentery causing bacteria. The one we focus on is shigella dysenteries. This causing blood to release in faeces.
what else can shigella cause
Not only are the receptors for these bacteria in the gut, they are also in the kidenys, so people with bad shigella end up with kidney disease.
