Topic 6.1 Bacteria and Disease Flashcards
Pathogenic bacteria
- Some bacteria are pathogenic.
- This means they re capable of causing disease in other organisms.
Tissue invasion
By growing and dividing in tissues, they can disrupt their normal function.
Toxin production
Bacteria release chemical toxins which can cause cell damage.
Endotoxins
- Toxins that are restricted to the bacterium cell wall.
- They are not freely released into the extracellular space or tissues.
- Cause cell damage around the site of infection.
The tissue Escheria coli invades
- The non-phagocytic eukaryotic cells.
- Eg. epithelial and endothelial cells.
Symptoms of Escheria coli
-Diarrhoea
-Stomach cramps
-Fatigue
-Nausea and vomiting
Exotoxins
- Soluble proteins.
- Released by bacteria and are free to move round the body.
- Very diverse.
- They can:
-act as enzymes to break down cells
-act as enzyme inhibitors to prevent normal enzyme functions.
The name of the bacterium that causes tuberculosis
Mycobacterium tuberculosis
How is TB spread?
Droplets from coughs/sneezes
Which people are vulnerable to TB infections?
-Those with HIV/AIDS
-Young/elderly
-Pregnant women
-Those with compromised immune systems
Streak plating
Used to identify and isolate individual colonies.
Generation time
The time between divisions.
(Can be as short as 20 minutes or as long as hours/days).
Generation time using logs
2^x = y
log(2)y = x (x is the number of divisions)
Exponential growth rate
Measuring bacteria growth
Measuring the number of cells present at various time intervals.
How to get a viable cell count
- Haemocytometer are special microscopic slides with two viewing chambers.
- They’re used to count cells.
Turbidity
- How opaque (or cloudy) a solution is.
- The cloudier the solution, the higher the turbidity and the higher number
How can bacterial resistance be controlled?
-Controlling prescriptions
-Controlling use in agriculture
-Hospital hygiene measures
-Antibiotic guardians
-Isolation of patients
-Mass testing
-Infection monitoring
Growth curve of bacteria
Lag phase: bacteria adapting to new environment.
Log phase: rate is close to or at maximum.
Stationary phase: total rate is 0; cells made is equal to cells dying.
Death phase: death rate is increasing and growth is close to 0 (due to buildup of toxic waste products & lack of nutrients).
List the basic aseptic techniques
-Wipe surfaces with antibacterial cleaner
-Set up Bunsen burner nearby. Convection currents prevent microbes from entering culture
-Flame inoculating loop & neck of bottles before use
-Minimise time that vessels containing bacteria are open
-Sterilise all equipment eg. using an autoclave
-Wear protective clothing
Difference between a spread plate and streak plate
-Spread plate: distribute microorganisms evenly with a sterile spreader
-Streak plate: aim to obtain single colonies by rotating that plate to build layers of the culture on at least 3 separate streaks
How to conduct a cell count?
1) Dilute broth sample with equal volume of trypan blue to stain dead cells blue.
2) Use a calibrated haemocytometer with volume 0.1mm^3. 3) Count the cells in each of the sets of squares and calculate mean.
4) Number of bacterial cells = number counted x10^4 per cm^3.
How to conduct a turbidity measurement?
1) Use colorimeter. Measure absorbance or % transmission of samples with known microorganism count.
2) Plot calibration curve: absorbance/ % transmission (y-axis), number of microorganisms (x-axis).
3) Record absorbance/ % transmission of unknown sample. Interpolate graph.
Advantages and disadvantages of using a turbidity
+ Quick
+ Can be conducted in the field
- Expensive equipment
- Counts both living & dead cells
-Required calibration curve from unknown samples
- Assumes equal density of cells across culture
How does Staphylococcus cause disease?
Secretes soluble proteins called exotoxins eg:
-Barrel-shaped proteins embed in host cell membrane so contents leak
-Protease toxins
-Superantigens trigger 20% of T cells (usual 0.001%) so can cause toxic shock.
How does Mycobacterium tuberculosis cause disease?
1) Triggers inflammatory response by infecting phagocytosis in lungs.
2) Infected phagocytes are sealed in waxy-coated tubercles so bacteria remain dormant. First infection has no symptoms.
3) If another factor weakens immune system, bacteria become active and destroy lung tissue.
Wha causes antibiotic resistance?
1) Random genetic mutation, often on plasmid, confers resistance eg. antigen shape changes
2) These bacteria have selective advantage in the presence of antibiotics, reproduce & pass allele for resistance to offspring
3) Directional selection results in resistant strain.
What causes antigen variability?
1) Random genetic mutation changes DNA base sequence
2) Results in different sequences of codons on mRNA
3) Different primary structure of antigen = H-bonds, ionic bonds & disulphide bridges form in different places in tertiary structure
4) Different shape of antigen.
How does antigen variability affect the incidence of disease?
- Memory cells no longer complementary to antigen => individual not immune => can catch the disease more than once/ cannot recognise pathogen eg. HIV.
- Many varieties of a pathogen => difficult to develop vaccine containing all antigen types.
Salmonella
- Gram-negative
- Endotoxins
Why is streak plating useful?
- Only one colony can grow
- Colonies spread out on agar
- Separating individual bacteria
- So colonies are separated
- So only 1 type of bacteria can be picked up
