Virulence Flashcards
Define virulence:
the ability of a pathogen to cause disease
How can virulence be measured/estimated?
By the lethal dose which is the amount of agent it takes to kill 50% of a group of animals in a test group. The more highly virulent the pathogen, the less amount of agent required to kill 50%.
Define attenuation:
This is a method of vaccination as the virulence of the pathogen is greatly reduced so can be given as a vaccine
What is the difference between toxicity and invasivness in terms of pathogenesis?
Toxicity is when the pathogen produces toxins to inhibit cell function whereas invasiveness is simply the growth of pathogen in host tissue without releasing toxins
What is a capsule as a virulence factor?
a polysaccharide coat around the bacterial cell
What is a pillus as a virulence factor?
to attach a bacterial cell to specific surfaces or to other cells
What causes diptheria and what is it?
Corynebacterium diphtheria
gram +ve,
non motile
club shape
What causes whooping cough?
Bordetella pertussis
gram-ve
aerobic cocco bacillus
confined to humans
What is the pathogenesis of whooping cough?
attach and replicate on ciliated URT mucosa and produce 3 types of toxins:
a) pertussis exotoxin (released outside the organism)
b) Tracheal cytotoxin
c) invasive adenylate cyclase toxin
- can cause secondary pneumonia
What causes cholera?
Vibrio cholera
comma shaped
gram -ve
What is the pathogenesis of cholera?
acute infection of GI tract by production of cholera toxin and adenylate cyclase upregulation
Give 3 examples of a partially invasive pathogens?
E.coli, influenza and shigellosis
What are the 3 examples of non-invasive pathogen diseases?
cholera, diptheria and whooping cough
What causes shigelloisis? (blood and puss in diarrhoea)
shigella sonnei for mild infections
shigella flexneri for severe infections
shigella dysenteriae for very severe
gram -ve rods, facultative anaerobes, non spore forming
What is the pathogenesis of shigelloisis?
shiga toxin causes partial invasion of membrane
Give an example of invasive pathogenic disease:
enteric fever
What causes enteric disease (typhoid)?
salmonella enterica - systemic infection causing constipation, fever and has a 3 week duration
How is typhoid transmitted?
person to person through contaminated foods and primary infection is through the jejunum or SI
What is an example of a disease without bacterial colonisation?
Food poisoning which is the consumption of food containing toxins e.g. botulism, staphylococcus aureus and bacillus cereus
What is the pathogenesis of diptheria?
It causes a thick covering (pseudomembrane formed) at the back of the throat leading to difficulty breathing and swallowing so is vaccinated against as a child. An AB (activity and binding function) toxin produced by the bacteria causes this damage, inhibiting protein synthesis (EF2)
Describe botulism food poisoning:
- ingestion of botulinum toxin produced by clostridium botulinum
- obligate anaerobe
- spore forming
- gram +ve
- heat stable
Describe staphylococcus aureus food poisoning:
toxin ingested interacts with gastric mucosa causing enterotoxins, rapid symptoms (caused by creamy foods, custards etc)
Describe bacillus cereus food poisoning:
- obligate anaerobe
- spore forming
- 2 disease forms:
a) emetic toxin - heat stable, short incubation
b) enterotoxins Nhe and EBL - heat labile, longer incubation and diarrhoea forming - grows in rice
