topic 6 Flashcards
How to carry out aseptic technique
- Decide which microorganisms to culture
- Provide these with appropriate nutrients In a sterile nutrient medium eg blood
- Some microorganisms may need to be grown In a selective medium
- Inoculate culture
- Broth = use an inoculating loop and swirl in culture
- Agar = make a streak plate
What is a pour plate ?
Molten agar is inoculated before it solidifies , it’s used to count the number of microorganisms in a mixed sample. Colonies uniformly distributed throughout the solid medium
What’s a spread plate
distribute microorganisms evenly using a sterile spreader
What’s a streak plate
Aim to obtain single colonies by rotating the plate to build layers of the culture on at least 3 sperate streaks
4 phases of bacterial growth curve:
lag phase - microorganism are adjusting to new environ so aren’t yet reproducing at measurable rate
log (exponential growth) - after every round of division population size doubles
stationary phase - total growth rate is 0 .
death phase - reproduction has almost stopped, death rate increases
Bacteria can affect the body through 3 ways
( toxins produced as biproduct of their chemical reactions)
Endotoxins
Exotoxins
Host tissue invasion
(Iipopolysacharides) Endotoxins come from salmonella
-lipopolysaccharides
-endotoxins released from GN bacteria only
-released from dead bacteria
-effects come later
staphylococcus aureus releases exotoxins
-proteins
-exotoxins are released by both GP and GN bacteria
-exotoxins released from living bacteria
Host tissue invasian - tuberculosis
- Bacteria inhaled as droplet infection
- Bacteria reach alveoli, they replicate by mitosis
- Immune system responds to the infection and macrophages will ingest bacteria
- This is the primary TB infection
- Tubercules r formed
- Later in life bac may remerge tubercules and bac start to reproduce (secondary tb infection)
- Bac destroy lung tissue
- Damaged lung tissue is is coughed up and without treatment tb can spread far in the body
What are antibiotics
Substances that kill or inhibit the growth of bacteria
Bacteriostatic antibiotic - tetracycline
Inhibit bacterial growth by stopping cells replicating (dna replication) , so no binary fission
Targets both GN and GP bac = broad spectrum(affective against a wide range of bac)
Bactericidal - penicillin
Only works on GP bacteria as it prevents the formation of cross links in the thick peptidoglycan layer of the cell wall
when water enters cells by osmosis the cell wall breaks and cell lysyes
-kills bacteria
Factors that affect anti microbial drugs (substances used to kill or inhibit the growth of microorganisms including bacteria) . Antibiotics is an eg
- Conc of drug in area of body affected
- Local pH
Use of broth cultures
Use of agar culture
Liquid culture.
Contains agar
An antibiotic is only effective if ..
The bacteria has a binding site for the a.b and a metabolic process the ab can interfere with
Mutations in bacteria can result in
-change in enzyme structure eg Making. Anew cell wall impermeable to the drug ,
What is a superbug
A strain of bacteria that’s become resistant to multiple antibiotics making it difficult to treat using standard antibiotics
To reduce the selection pressure (use of antibiotics ) we need to
Only use antibiotics when necessary and complete the course of antibiotics
Healthcare associated infections are transmitted thru poor hygiene
-no washing hands before and after visiting patient
-coughs and sneezes not being contained
Codes of practice to prevent spread of HCAIs
-everyone encouraged to wash hands
-clothing worn by workers should be disposable
-equipment and surfaces should be disinfected
How can u reduce the spread of resistant bacteria
-Dr shouldn’t prescribe A.B for minor infections
-dr should use narrow spectrum A.B because your therefore reducing selection pressure
Why are doctors advised to limit prescriptions of antibiotics
Antibiotics act as selection pressure, some bacteria resistant to antibiotics, resistant bacteria survive and reproduce and pass on gene
Viral infections are often specific
To particular tissues
Transmission of flu virus
Mode of infection
Pathogenic effects
Treatment/control
-Through Droplet infection, direct contact with animal faeces
- infects ciliated epithelial cells of the lungs, lyric cycle
-headache, sore throat
—antiviral medication
Stem rust fungus transmission
Mode of infection
Pathogenic effects
Wind carries spores from infected plants
Spore lands on host but needs water to germinate , hypha emerge from spore and penetrate one of the stomata from the leaves , hypha secrete enzymes to digest the plants and absorb nutrients.
Absorbs nutrients from plant reducing yield , pustules on epidermis burst making transpiration harder to control.
How can stem rust be controlled
Using fungicides to kill fungi, expensive
Transmission of malaria
Mode of infection
Pathogenic affect
-infected mosquito bites human, parasite reproduces rapidly in the liver, parasite gets into bloodstream and invades red blood cells, they reproduce further, infected red blood cells burst , this leads to fever
-fever , chills, liver damage , can eventually lead to death
Plasmodium spp is the disease and malaria is
The symptoms
Malaria treatment
Mosquito nets, insect repellent
Malaria is an endemic disease what is this?
Why is endemic diseases difficult to control?
A Disease always present in a country
Expensive to provide treatment, difficult to remove all sources of infection
How can malaria an endemic disease be controlled
Preventing mosquito bites through insect repellents, controlling mosquito numbers by removing standing water and sewage.
Ethical , social and economical implications of control measures for malaria
Ethical - informed consent may be difficult
Social - people need to change their customs eg start sleeping with mosquito nets
Economical - prevention of endemic diseases is very expensive
How to construct a streak plate
Flame a wire loop
First streaks of sample in straight lines on the surface of sterile agar plate
- at least 3 streaks
Why should agar plates be incubated below 30 degs in a school laboratory
Above 30 is close to human temp
-risk of incubating human pathogens which could infect students
Name three structures present in prokaryotic cells but absent In animal
Plasmids , single circular chorosmome , cell wall
Name 2 ways u can distinguish different bacterial colonies grown on the same agar plate
Colour and shape
Why is aspect technique important even if the bacteria used r harmless
No contamination of cultures by microorganisms from environment
List a method used to estimate the growth of a bacterial culture?
Disadv
Turbidity measurement (as bac reproduce it incr the no. Of bac in culture , causing liquid medium to come cloudier overtime)
Can’t distinguish between alive and dead cells
What’s an antigen?
A substance that stimulates the production of an antibody when it gets in the body
What’s a physical and chemical barrier in the body?
Skin prevents entry of pathogens and hcl in stomach, the low ph kills bacterial pathogens
What are self antigens vs non self antigens?
Antigens produced by the organisms own body cells which don’t stimulate an immune response . Antigens found on bacteria and they do stimulate an immune response
Non specific responses
recognise the difference between self and non self
What’s an example of a non specific response?
Inflammation, histamines released by white blood cells cause vasodilstion which increases blood flow to infected area and increases permeability of capillaries, causing antibodies to leak out into infected tissue and destroy pathogens
Fever as a non specific response to infection?
Hypothalamus sets body temp higher , decreases speed of pathogen reproduction and increases rate of specific immune response
Lysozyme action as a non specific response to infection ?
Lysozyme found in tears and mucus which kill bacterial cells by damaging their cell wall
Phagocytosis as a non specific response to infection ?
Phagocyte engulfs pathogen into a vesicle which fuses with lysosome , digesting the pathogen
What are the 2 main types of phagocytes ?
Neutrophills and macrophages
Opsonins
Chemicals which bind to pathogens making them more easily recognised by phagocytes
The specific immune response..
Is antigen specific and produces responses specific to one type of pathogen only . This type of response relies on lymphocytes produced in the bone marrow
what are the 2 types of white blood cells
B and T lymphocytes
-macrophages
what happens in the humoral response stage 1 (consists of 2 stages: T helper activation and the effector stage)
- pathogen engulfed by a macrophage
- macrophage digests pathogens and displays the antigens on MHCs
- macrophage becomes an antigen presenting cell (APC)
- macrophage APC binds to T helper cells w complimentary receptors
- T helper cells r activated and divide to form activated T helper cells and T memory cells
what happens in the humoral response stage 2 - the effector stage
- Pathogen binds to B cell with complimentary receptors
- B cell engulfs pathogen & displays antigens on MHCS
- B cell becomes APC
- ACTIVATED T HELPER cell binds to APC and produces cytokines that stimulate the B cell.
- B cell divides by clonal selection into B memory & effector cells
- effector cells/ b memory cells differentiate into plasma cells and produce antibodies
- memory cells circulate within blood and tissue
there are 2 types of WBC one type is B and T lymphocytes
3 types of B cells : B effector cells which divide to form plasma cell clones
plasma cells which produce antibodies to antigens
B memory
there are 2 types of WBC one type is B and T lymphocytes
3 T cells : T killer cells, T helper cells which activate plasma cells to produce antibodies against the antigen on a particular pathogen
t memort cells
displays antigens on cell surface membranes
mhcs
Explain how phagocytosis and lysozyme action lead to antigen presentation by macrophages
Pathogen engulfed and taken in by macrophage
Fusion of phagosome with lysosome
Pathogen digested
Antigens presented on outer surface of macrophage
Describe a features of antibodies
-Y shaped to create 2 antigen binding cites
Where are B and T cells produced
What takes place in the cell mediated response
- Pathogen invades body cell
- Infected body cell displays antigens on mhcs
- Infected body cell becomes apc
- T killer cell with comp recep binds to APC
- Cytokines from active T helper cells stimulate killer cells to divide into active t killer cells and t killer memory cells
- t killer cells destroy cells infected with virus
- s0 virus can be engulfed by a macrophage
Explain the importance of antibodies in fighting bacterial pathogens (4)
- Each antibody can bind to 2 bacteria resulting in agglutination
- Antibody causes opsonisation
- Toxins neutralised
Explain why both t helper cells and t killer cells r needed
T helper cells stimulate B cells to divide
T helper cells stimulate t killer cells to divide
Bc t killer cells destroy cells
There are two types of immunity what are they?
Passive immunity - It results from the introduction of antibodies from another person or animal
Active immunity - It results from the production of antibodies by the immune system in response to the presence of an antigen
There are 2 different types of active immunity
What are they
Natural - This is when you become immune after being infected by a pathogen
Artificial - this is when you become immune after you’ve been given a vaccine containing antigens
There are 2 types of passive immunity what are they
Artificial -Become immune after being injected with antibodies
Natural - a baby becomes immune due to the antibodies it receives from its mothers breast milk
How
Does being vaccinated give u immunity without getting the disease
Being vaccinated means when a pathogen enters the body you respond quicker to the infection bc the vaccine already caused a primary response so there are memory t and b cells that can quickly respond to the infection
Pros and cons to vaccines
Pros - gives protection to the individual against a disease, cost of treating the disease is kept to a minimum
Con - people may have allergies , some children become ill after vaccination with an extreme immune response
Why would the lvl of antibodies increase during an infection for someone who’s vaccinated
- Secondary response
- Memory cells circulate within blood and tissue
- During infection memory cells r activated
why are there relatively few species of bacteria in the stomach
pH inside the stomach is too low for enzymes of most bacteria to function
-bacteria that live in the stomach have adaptations allowing them to survive
Distinguish between the structure of bacteria and viruses
Bacteria contain a cell wall, viruses contain a capsid coat
Bacteria have ribosomes plasmids don’t have ribosomes
Bacteria have circular genetic material viruses have straight genetic material
How can malaria lead to anaemia
Malarial parasite invades red blood cells
Therefore reduced haemoglobin red cell count which causes anaemia
Why are data about people with HIV infections often estimates
-Many ppl r unaware they have infection because bc it doesn’t alw produce symptoms
-it’s impossible to test every human
