Topic 6 Flashcards
How can malaria be prevented?
Mosquito nets, insect repellent, pesticides, proper disposal of sewage, drain wetlands where mosquitoes breed, vaccination
How does Mycobacterium tuberculosis attack a cell?
-By host tissue invasion
-Tubercles are coated in thick waxy coat that when engulfed by phagocytosis, it survives
-Lies dormant in tubercles and not destroyed by immune system
How does Salmonella attack a cell?
By endotoxins
How does Staphylococcus (MRSA) attack a cell?
By exotoxins (gram positive)
How do pathogens harm the host?
Invade and destroy host tissues
Produce toxins
How do you isolate a singular microorganism from a culture?
streak plating
How do you make a serial dilution?
- Start with 10cm^3 of undiluted culture
- Add 1cm^3 of first tube into 9 cm^3 of sterile saline
- Continue to add 1cm^3 from previous tubes to more 9cm^3 solutions to form serial dilutions
How do you produce an aseptic culture?
Provide organisms with appropriate nutrients
Use a sterile medium
Use an sterile inoculating loop to transfer pathogen
Prevent contamination from air (convection current)
Pass bottle through flame
Only open lids partway
How do you sterilze equipment before or after use?
Using UV Light or an autoclave.
How is a direct cell count calculated?
A haemocytometer (a glass slide with a grid etched on) is placed on a slide
Count Bacteria cells in, touch top line, and touch left line
Only count viable cells
How is an indirect cell count used to measure dry mass of cells?
- Filter a sample of known dilution through a pore
- Remove water by evaporation
- subtract final mass from initial mass (including filter paper) to calculate mass of dry microorganisms
How is an indirect cell count used to measure turbidity of a diluted culture?
The cloudiness of a sample can be calculated using a simple colorimeter to measure absorbance or transmission.
A haemocytometer can be used produce a calibration curve that relates to absorbance or transmission to the the actual number of cells.
How is influenza transmitted?
via droplets generated when infected persons cough or sneeze; animal waste; infected surfaces
How is MRSA prevented?
New patients screened, isolated and treated
Antibiotics only used if needed
Antibiotic courses completed
Strict hygiene regimes
How is Stem Rust Fungus Transmitted?
Airborne spores of fungus
Infected plant fragments in soil
How is the spread of antibiotic resistance controlled?
Isolating infected people
Hand washing and antibacterial gel
Gloves and aprons
Restricting use of antibiotics
Completing courses of antibiotics
Developing new antibiotics
What are all the types of white blood cells
Three groups:
PHAGOCYTES
- nuetrophils
- monocytes -> Macrophages
Lymphocytes
- T cells
- B cells
Eosinophils
What are bactericidal antibiotics?
Antibiotics that kill bacteria by destroying cell walls causing bacteria to burst
Especially effective against Gram-positive as cell wall is so thick
(e.g. penicillin)
What are bacteriostatic antibiotics?
Antibiotics that inhibit the growth of bacteria by stopping protein synthesis and production of nucleic acids so bacteria cannot replicate
Especially effective against Gram-negative as lipid bilayer is damaged
(e.g. tetracycline)
What are cytokines?
chemical messengers produced in response to a stimulus
What are physical barriers to infection?
Skin
Stomach acid (kills bacteria)
Gut and skin flora (natural bacteria flora competes with pathogens for food and space)
What are some non-specific responses to infection?
Inflammation: Histamines released by damaged white blood vessels and cause vasodilation to increase speed of delivery of antibodies
Fever: Hypothalamus increases body temperature to decrease speed of pathogen reproduction
Lysozyme action: Lysozyme (enzyme) kills bacterial cells by damaging the cell wall
What are the benefits and drawbacks of using serial dilutions to calculate cell count?
Benefits: cheap and simple
Drawbacks: Only counts viable cells; very slow due to incubation period and serial dilutions
What are the differences between endotoxins vs exotoxin?
An answer that makes reference to two of the following:
* endotoxins released from Gram-negative bacteria (only) but exotoxins released from both Gram-negative and Gram-positive bacteria (1)
* endotoxins are lipopolysaccharides but exotoxins are proteins (1)
* endotoxins released from {dead / broken down} bacteria but exotoxins are released from living bacteria (1)
* effect of endotoxins is later (1)
What are the different types of culture media?
Liquid (broth)
Solid (grows cultures with discrete colonies)
Non-selective (allows broad range of microorganisms to grow)
Selective (allows only a narrow range of microorganisms to grow)
What are the drawbacks of measuring turbidity?
Have to use a direct method to calculate cell count from calibration curve
Expensive
Assumes cell density is equal across culture
What are the ideal conditions for growth?
Nutrients
- Suitable temperature
- Suitable pH
- Varying access to O2 (Most anerobic conditions can lead to growth of pathogens)
What are the issues with malaria prevention
Not possible to drain wetlands that people use
Insecticides could have unexpected effects to food chains
Expensive to develop vaccines
What are the pathogenic effects of influenza?
Lysis of cells and release of toxins cause coughing, headache, vomiting and other symptoms
What are the steps of streak plating?
- Flame inoculating loop
- Dip loop in culture
- Make three streaks on sterile plate
- Turn the plate 90 degrees and streak again, overlapping last streaks
- Turn and streak again
- use isolated colonies to prepare a second plate
What are the scientific name of red and white blood cells:
Red: Erythrocytres
White: Leucocytes
What are the two types of cell count?
Total count: All cells in the culture, dead or alive
Viable count: Only the living cells in the culture
What are the types of antibody actions?
- Opsoniation: Coated to be detected by phagocytes
- Precipitation: Inhibit toxins that are released or make them insoluble
- Agglutination: Clumps microoganisms together for easier phagocytosis
- Lysis: Breaks open bacteria cells
What causes antibiotic resistance to develop?
Natural Selection: a mutation will create an allele of a gene which changes the effect of the antibiotic. Antibiotic resistance will be passed on to offspring increasing its frequency. A selection pressure cause the frequency to increase because the allele puts them at a survival advantage.
What do macrophages do?
Ingest not only foreign cells but also body cells that are dead or dying (Non-specific immune response), but also initiate a specific immune response
Display antigen of digested bacteria on surface membranes through antigen/MHC complex
Release cytokines to attract other phagocytes to the site of infection, leading to inflammation
What does a neutrophil do?
Ingests bacteria cells, kills it then digests it (Non-specific immune response)
What happens when a lymphocyte binds to an antigen on an antigen presenting cell (APC) ?
The lymphocyte becomes sensitised and divides repeatedly to produce a clone of cells
Most become activated lymphocytes
What is an antigen?
A molecule that cause an immune response by lymphocytes, usally protiens or glycoprotiens
What is an Antigen-presenting cell?
A cell that isolates the antigen from a pathogen and places it on its surface membrane so that it can be recognised by other cells in the immune system through the MHC marker protiens
What is an endotoxin?
Associated with Gram-negative bacteria. An endotoxin is a lipopolysaccaride of a bacteria found in the outer membrane of the cell wall. These can be released when the bacteria breaks down making treatment difficult.
What is an example of a bacteria that releases endotoxins?
Salmonella
What is an example of a bacteria that releases exotoxins?
Staphylococcus aureus
What is an exotoxin?
A soluble protein produced and released by bacteria as they metabolise and reproduce
Found in both Gram-negative and Gram-positive bacteria. This can move through bodily fluids creating a wider effect than endotoxins.
What is a secondary immune response?
The response to infection caused by an antigen to which there are memory cells already present in the host’s body
What is clonal selection?
The repeated mitotic divisions of a sensitised lymphocyte to produce a large number of genetically identical cells
What is herd immunity?
Enough people are vaccinated to make transmission of a disease unlikely
What is host tissue invasion?
When bacteria invades and damages cells
What is phagocytosis?
When white blood cells engulf foreign cells and digest them. Lysosomes fuses with the entered vesicle and release hydrolytic enzymes that digest.
What is the cell-mediated immune response? (T-helper activation)
- A pathogen invades a host cell and the host cell becomes an Antigen-Presenting Cell (APC)
- An T cell binds to a surface receptor complementary to the antigen being presented and becomes activated. This is through CD4 receptor
- T helper cells secrete cytokines which stimulate T killer cells
- T killer cells destroy infected cells by binding to the APCs, releasing toxins that poisons the cell and activating genes that cause cell death (lysis by creating pores in membrane)
What is the death phase of bacterial growth?
A lack of nutrients and increase of toxic products cause death of microorganisms. Deaths exceed new cell production
What is the humoral immune response? (B-cell activation)
- A pathogen is engulfed by a macrophage and the cell becomes an Antigen-Presenting Cell (APC)
- T cells bind to the antigens on the APC and becomes sensitised releasing cytokines.
- The cytokines stimulate the B cells to become active and to divide and form B memory cells and B effector cells
- B effector cells become plasma cells which can produce antibodies which attack the pathoge
What is the lag phase of bacterial growth?
Slow growth of microorganisms as they adjust to their environment and nutrients avaiable
What is the log phase of bacterial growth?
exponential growth
What is the mode of infection of influenza?
- Ciliated epithelial cells are infected
- Viral RNA takes over biochemistry
- Cell produces new virus particles
- Cell lyses
- Many viral particles are released
- Virus taken into cells lining bronchi and bronchioles by endocytosis
What is the mode of infection of Malaria?
- Parasite transmitted via mosquito (Vector)
- Parasite travels to liver
- Parasite infects red blood cells
- Parasite reproduces asexually inside red blood cells and causes lysis
What is the pathogenic effect of Malaria?
Lysis of red blood cells causes sweating, shaking, anaemia and liver damage
What is the pathogenic effect of Stem Rust Fungus?
- Enzymes are produced to digest the plant
- absorbtion of its nutrients which causes stem to be shortened and weakened
- Uncontrolled water loss
What is the stationary phase of bacterial growth?
population reaches maximum due to limiting nutrients and a build up of toxic substances. Death rate = Division rate
What is the the mode of infection of Stem Rust Fungus?
- Spore germinates in water
- Produces hyphae which enters host by stomata
- Fungus grows into mycelium
- Fungus surrounds all tissues in the plant
Why is HIV hard to treat?
It has a constantly changing protein coat that means it is not recognised by the immune system
Why is there high resistance to antibiotics in bacteria?
- High mutation rate
- Reproduce rapidly
- Horizontal transmission of resistance (Plasmid exchange)
Why might some antibiotics only work on Gram (+) and some only on Gram (-)
- Gram + has a thick layer of peptidogylcan in their cell wall
- Some antibiotics inhibit the enzymes involved in the formation of peptidogylcan so are more effective in gram +
- Some antibiotics can’t cross this layer, and so are only effective against gram -
Why must aseptic techniques be used?
To prevent potentially harmful microorganisms escaping from culture to air
To prevent microorganisms from the air contaminating the culture, spoiling the investigation
Why should a culture temperature be around 30 degrees?
Temperature close the human body temperature encourages growth of pathogens
How is malaria transmitted
Virus enters the body in saliva of female mosquito
