XABY02 MICROBIAL DISEASES Flashcards
What is pathogenicity?
The ability of bacteria to cause harm
What are the two ways a bacterium can cause harm?
- Damaging host tissues by entering and reproducing inside cells
- Producing toxins
What are the four factors affecting pathogenicity?
- features of cell wall and capsule (affecting attachment and entry to host cell)
- types of toxins (endotoxins and exotoxins)
- infectivity of bacteria
- invasiveness of bacteria
What allows a bacterium to attach to protein receptors of host cell membrane?
The specific complementary structures of Ligands (polysaccharides) and Glycocalyx (glycoproteins) of bacterial cell wall
Aside from cell membrane binding, what are two other ways entry of bacteria can also occur?
- production of enzymes by pathogen, damages host cell membrane
- endocytosis, bacteria engulfed by host e.g. white blood
What is a toxin?
A molecule with harmful effects on the body
What are exotoxins?
Protein secreted or leaked from bacteria
What are endotoxins?
Lipopolysaccharides present in bacterial cell walls, usually released when bacterial cell wall breaks up after death
What determines infectivity?
The number of bacteria needed to cause infection
What is an example of a highly infective disease?
Typhoid Fever
What is an example of a disease that is not highly infective?
Food poisoning (caused by Salmonella)
What two diseases are caused by different species of Salmonella bacteria?
Typhoid Fever and food poisoning
What is invasiveness?
The ability of bacteria to spread from where it entered, to other tissues and to multiply here
Which systems play a part in the invasiveness of bacteria?
Lymph and blood (circulatory) systems
What two things must bacteria be able to do in order to be invasive?
- Avoid phagocytosis and all other body defences
2. To be able to get through tough fibres, connective tissues and intercellular cement
What two diseases are caused by particularly invasive bacteria?
- Bubonic Plague
2. Anthrax
What can invasive bacteria do in regards to toxins?
Produce toxins that spread through body and damage tissues far away from initial source of infection
What are the 6 methods of transmission of disease?
- airborne/droplet infection
- food-borne
- water-borne
- contact (skin to skin, clothing to skin)
- sexual intercourse
- vector-borne
How is Cholera transmitted?
Ingestion of water and rarely food contaminated by faecal material containing the pathogen
What kind of disease is Cholera?
water-borne
What bacteria is Cholera caused by?
Vibrio Cholerae
Give 3 ways that Cholera arise in communities
- drinking water not properly purified
- untreated sewage leaks into water courses
- food contaminated by those preparing/serving it
Does Vibrio Cholerae posses a flagellum?
Yes
How is diarrhoea treated?
By restoring water and ions lost by Oral Rehydration Solution
What 4 things does an Oral Rehydration Solution contain?
Water, sodium ions, chloride ions and glucose
Why is ORS successful in treatment of diarrhoea?
It uses the co-transport protein, which bacterial infections tend not to have an effect on
What are the 5 symptoms of Cholera?
- diarrhoea
- dehydration
- stomach cramps
- vomiting
- fever
What are the 4 steps of the process of the Oral Rehydration Solution?
- sodium ions and glucose in ORS taken up by co-transport protein in epithelial cells
- water potential of epithelial cell reduced and lower than water potential of lumen
- water in ORS solution then moves from lumen to cell by osmosis
- water moves into blood and patient rehydrated
How does Vibrio Cholerae
cause harm?
Bacteria produce a toxin that acts on epithelial cells of small intestine which causes changes in membrane permeability
What is the process in which the Vibrio Cholerae toxin causes symptoms of Cholera? (7 STEPS)
- toxin binds to protein receptor in cell membrane of epithelial cells of small intestine
- shape of toxin complementary to binding site on receptor
- attachment of toxin to receptor causes ion channels to open
- chloride ions diffuse into lumen of intestine
- lowers the water potential of the lumen, and raises the water potential of epithelial cells
- water flows along water potential gradient from cells and blood into lumen by osmosis
- which causes diarrhoea
Why were trialled Oral Rehydration Solutions with more glucose tested and rejected?
- Additional glucose lowered water potential in lumen of small intestine
- So much it started to draw even more water from epithelial cells
- made dehydration even worse
In developing and testing ORS, what was used instead of glucose and why? (3 reasons)
Starch
Because:
1. it is insoluble and has no osmotic effect
2. it is slowly hydrolysed by amylase and maltase to glucose monomers
3. because glucose is released slowly from starch, it can be taken up at same rate by co-transport
