Topic 6: Immunity, Infection And Forensics Flashcards
Virus structure
Non-living
- consist of a nucleic acid, enclosed in a protective protein coat called the capsid
- covered with a lipid layer called the envelope
Bacteria and viruses differences
- bacteria are prokaryotes
- bacteria do not require a host to survive
- viruses are smaller
- bacteria have organelles
TB explain
- caused by the bacteria mycobacterium tuberculosis
- spread through lipid droplets which are inhaled by another person causing the bacteria to move into lungs
- in the lungs, the bacteria is engulfed by a phagocyte. in TB the bacteria are able to survive and replicate from inside the phagocyte
- first infection may be symptomless. Infected phagocytes are sealed in tubercles in the lungs as a result of inflammatory response
- bacteria lie dormant inside the tubercles. Not destroyed by immune system as have a thick waxy coat
- when immune system is weakened, bacteria becomes active again
- spreads to other parts of the body, which means they can be fatal
HIV explain
-destroys T helper cells in the immune system leading to AIDS
- the first symptoms of HIV are flu like
- after several weeks HIV antibodies appear in blood
- symptoms disappear until the immune system becomes weakened again, leading to AIDS
- symptoms include weight loss, dementia and cancers
name three physical barriers to infection
- skin - tough physical barrier consisting of keratin
- stomach acid and enzymes - kill bacteria
- gut and skin flora - natural bacteria flora competes with pathogens for food and space
antibiotics definition and the two types
used to fight infection by killing the bacteria and stopping their growth.
- bactericidal antibiotics: kill bacteria by destroying their cell wall, causing them to burst
- bacteriostatic antibiotics: inhibit the growth of bacteria by stopping protein synthesis and production of nucleic acids so bacteria cant divide
how do bacteria become resistant to antibiotics
- as a result of natural selection
- bacteria not killed by the antibiotic possess a selective advantage - resistance which enables them to survive and reproduce
- the allele for AR is passed onto offspring creating a resistant strain
- pathogens also evolve adaptations which allow them to survive and reproduce
how do hospitals control the spread of antibiotic resistant infections
- new patients are screened at arrival and then isolated and treated
- antibiotics only used when needed and the course is completed to ensure all bacteria are destroyed, and to minimise selection pressure on bacteria
- no use of antibiotics for minor infections or viral diseases
- rotate the use of antibiotics
- strict hygiene regimes
- wearing suitable clothing to minimise transmission
what is RNA splicing
a post transcriptional modification of mRNA which enables eukaryotes to produce more proteins than they have genes. enables more than one protein to be made from one gene
how does RNA splicing occur
- a gene is transcribed which results in pre-mRNA
- all introns and some exons are removed
- remaining genes are joined back up by enzyme complexes called spliceosomes.
- the same exons can be joined in a variety of ways to produce several versions of mature functional RNA
explain degree of muscle contraction
- after death, muscles begin to stiffen as ATP is used up, calcium ions build up and become fixed in a state of contraction
- this is rigor mortis and the extent of it can be used to determine time of death
what are introns
non coding regions of DNA
- consist of many repeating base sequences known as short tandem repeats in sections called satellites
what are extrons
coding regions of DNA
what are the four main ways in which pathogens can enter the body
- broken skin: this provides direct access to the tissues and bloodstream
- the digestive system: when we consume contaminated food or drink
- the respiratory system: every time we inhale
- mucosal surfaces: the lining of body cavities eg inside of nose , mouth
how do antibiotics work
- inhibiting bacterial enzymes needed to form bonds in the cell walls; this prevents growth and causes death. cell walls are weakened and burst under the pressure of water entering via osmosis
- binding to ribosomes and preventing protein synthesis - the ribosome shape is altered, thus the mrna is prevented from binding to the ribosome, so translation cannot occur and the protein is not synthesised
- damaging cell membranes, leading to a loss of useful metabolites
- preventing bacterial DNA from coiling into rings, meaning that it no longer fits into the bacterial cell.
what factors can be used to determine time of death
- extent of decomposition
- stage of succession
- forensic entomology
- body temp of the deceased
- degree of muscle contraction
how can extent of decomposition be used to determine time of death
- visually by looking at the appearance of the body
- after a few days: skin will appear greenish in colour
- after a few weeks: gases such as methane produced, which leads to bloating. the skin will blister and fall off the body.
- a few weeks after this the tissue turns to liquid
what is rate of decomposition affected by
- temp
- availability of oxygen
- Decomposition would be slower in anaerobic conditions and at lower temperatures
what stages of succession would the body undergo if above ground
- bacteria will be found in and on the body immediately after death
- tissue decomposition creates ideal conditions for flies to lay eggs and their larvae to hatch
- this creates good conditions for beetles to establish
- when tissue dries out, flies leave
- beetles remain
what can body temp tell us of TOD
- once a person dies metabolic reactions end.
- since no more heat is being produced, body temp drops (this process is algor mortis)
- body temp decreases 1.5-2 degrees per hour
what does muscle contraction tell us about TOD
- muscles in the body begin to contract about 4-6 hours after TOD. this is rigor mortis.
- rigor mortis will begin in the head and end in the lower body
- rm wears off about 24-36 hours from TOD.
- this process is affected by the evel of muscle development and the temperature of the surroundings: Higher temperatures will speed up the rate of rigor mortis
how do hospitals limit the spread of hospital-acquired infections
Staff and visitors must wash hands regularly while visiting patients
If a person contracts a HAI they should be moved to an isolation ward to prevent spread of the infection
Surfaces and equipment must be disinfected after every use
increased washing of bedding
testing patients for the presence of antibiotic resistant bacteria before admission
staff not to wear ties/ long sleeves
what can forensic entomology tell us about time of death
- a dead body provides the ideal habitat for many species of insects
- different insect species will colonise a body at different times after death: flies will be found after a few hours, beetles later
- another clue insects provide is the stage of life cycle that they are at
forensic entomology definition
the study of insect colonies on a dead body
factors that might affect the progression of insect life cycles
- drugs present in the body
- humidity
- oxygen availability
- temperature
decomposition and nutrient recycling
- dead plants and animals are broken down by microorganisms such as bacteria
- these decomposers secrete enzymes that break down large molecules into smaller ones
- the microorganisms involved in decomposition produce CO2 and methane which are released into the atmosphere
- carbon dioxide can then be absorbed by green plants which will fix the carbon back into carbohydrates during photosynthesis
how can dna profiles be created
- isolating a sample of dna eg from saliva
- producing more copies of the DNA fragments in the sample using PCR
- carrying out gel electrophoresis on the DNA produced by PCR
- analysing resulting pattern of DNA fragments by visualising the gel using UV light
what are the four main barriers to infection
- skin: provides a physical barrier to infection. blood clotting plays an important role in preventing pathogen entry also.
- microorganisms of the gut and skin: compete with pathogens for resources, limiting their numbers and their ability to infect the body
- stomach acid: hcl creates an acidic environment unfavourable to many pathogens
- lysozyme: secretions of the mucosal surfaces contain an enzyme called lysozyme. this enzyme damages bacterial cell walls
what are the two types of immune response in the body
non specific: the same, regardless of the pathogen
specific: specific to a particular pathogen
antigen definition
molecules such as proteins or glycoproteins located on the surface of cells: their role is to identify cells as being ‘self’ or ‘non self’
stages and explanations of the non-specific immune response
- inflammation:
- the surrounding area of a wound becomes swollen, warm and painful: this is inflammation
- body cells called mast cells respond to tissue damage by secreting histamine
- histamine is a chemical signalling molecule
- histamine stimulates the following response
(1) vasodilation increases blood flow through capillaries
(2) capillary walls become more permeable, allowing fluid to enter and creating swelling
(3) phagocytes leave the blood and enter tissue to engulf foreign particles
(4) cells release cytokines, another cell signalling molecule - interferons
- cells infected by viruses produce anti viral proteins called interferons which prevent viruses from attaching to uninfected cells
- they inhibit the production of viral proteins, preventing viral replication and infecting more cells
- they activate T killer cells to destroy infected cells
- they stimulate inflammation to bring more immune cells to the site of infection - phagocytosis
- phagocytes travel throughout the body and can leave the blood by squeezing through capillary walls
- during an infection they are released in large numbers
phagocyte definition
type of white blood cell responsible for removing dead cells and invasive microorganisms
phagocytosis explained
- chemicals released by pathogens attract phagocytes to the site where the pathogens are located
- they move towards pathogens and recognise the antigens on the surface of the pathogen as being “non-self”
- the cell surface membrane of a phagocyte extends out and around the pathogen, engulfing it and trapping it within a phagocytic vacuole
- enzymes are released into the phagocytic vacuole when lysosomes fuse with it
- these digestive enzymes, which includes lysozyme, digest the pathogen
- after digesting the pathogen, the phagocytes, the phagocyte will present the antigens of the pathogen on its cell surface membrane
- The phagocyte becomes what is known as an antigen presenting cell
- The presentation of antigens initiates the specific immune response
difference between self antigens or non-self antigens
self : antigens produces by the organisms own body cells
non-self: antigens not produced by the organisms own body cells.
- non self antigens stimulate an immune response
antibody structure
- y shaped molecules sometimes known as immunoglobulins
- four polypeptide chains: two heavy chains attached by disulphide bonds to two light chains
- each pp chain has a constant region and variable region: the constant regions do not vary within a class of antibody, the amino acid sequence in the variable region are different for each antibody.
- the variable region is where the antigen binding site is located
- the hinge region, gives flexibility to the antibody molecule, allowing the antigen binding site to be placed at different angles
variable region structure and function
- where the antibody binds to an antigen to form an antigen antibody complex
- at the end of the variable region is the antigen binding site
difference between membrane bound of secreted directly into the blood antibodies
- membrane bound are attached to the surface of the lymphocytes
- they have an extra section of polypeptide chain within their heavy chain which forms the attachment to lymphocytes
- This extra section of polypeptide is not required in antibodies that are not bound to lymphocytes
- The gene which codes for the antibody heavy chains can undergo a process called alternative splicing to remove this extra section in non-bound antibodies
difference between splicing and alternative splicing
Splicing removes non-coding sections of mRNA called introns, while alternative splicing removes coding sections called exons; in this case the exons that code for the the extra section of the heavy chains are removed
antibody function
- antibodies bind to speciffic antigens that trigger the specific immune response
- antibodies function to disable pathogens in several ways:
1. Pathogens enter host cells by binding to them using receptors on their surface; antibodies can bind to these receptors, preventing pathogens from infecting host cells
2. Antibodies can act as anti-toxins by binding to toxins produced by pathogens, e.g. the bacteria that cause diphtheria and tetanus; this neutralises the toxins
3. Antibodies cause pathogens to clump together, a process known as agglutination; this reduces the chance that the pathogens will spread through the body and makes it possible for phagocytes to engulf a number of pathogens at one time
what are T cells
type of white blood cell involved with the specific immune response
- they are produced in the bone marrow and finish maturing in the thymus
- mature T cells have specific cell surface receptors called T cell receptors
how do activated T cells divide and into which four main types
- divide by mitosis to increase in number
1. t helper cells: release chemical signalling molecules (cytokines) that help to activate B cells
2. T killer cells: bind to and destroy infected cells displaying the relevant specific antigen
3.t regulatory cells: suppress other immune cells and prevent them from attacking our own host cells
4. t memory cells: remain in the blood and enable a faster specific immune response. if the antigen is detected at a later date, they divide into T helper, T killer and T regulatory cells
B cells definition and function
- second type of white blood cell in the specific immune response
- b cells remain in the bone marrow as they mature
- they have specific receptors on their membrane
explain the B cell response
If the corresponding antigen enters the body, B cells with the correct cell surface antibodies will be able to recognise it and bind to it
When the B cell binds to an antigen it forms an antigen-antibody complex
The binding of the B cell to its specific antigen, along with the cell signalling molecules produced by T helper cells, activates the B cell
Once activated by chemicals from T helper cells or when the antibody molecules on their cell surface bind to a complementary antigen, the B cells divide repeatedly by mitosis, producing many clones of the original activated B cell
The daughter cells differentiate into two main types of cells:
Effector cells, which go on to form plasma cells
(Plasma cells produce specific antibodies to combat non-self antigens)
Memory cells
Remain in the blood to allow a faster immune response to the same pathogen in the future
active immunity
- aquired when an antigen enters the body triggering a specific immune response
- can be natural (exposure to pathogens), or artificial (acquired through vaccination)
- in both cases the body produces memory cells, giving the person long term immunity
passive immunity
- aquired without an immune response
- can be natural
(foetuses receive antibodies across the placenta from their mothers, babies receive antibodies in breast milk) - can also be artificial
(people can be given an injection of antibodies) - no memory cells to enable a secondary response
vaccines definition and explain
- contains antigens that are intentionally put into the body to induce artificial active immunity
- produce long term immunity as cause memory cells to be created
-The immune system recognises the antigen when re-encountered and produces antibodies in a faster, stronger secondary response
antigenic variation
- pathogen may muatate frequently so that its antigens change suddenly rather than gradually, weakening effectiveness of vaccine
vaccinations need to be constanlty modified to keep up with changes to a pathogen’s antigens resulting from mutations
HIV evasion mechanisms
- the virus kills helper T cells after it infects them which reduces the number of cells that could detect the presence of the virus and activate production of antibodies
- HIV shows antibiotic variability due to the high mutation rate in the genes coding for antigen proteins. this forms new strains of the virus which each require a new primary immune response
- the virus prevents infected cells from presenting their antigens on the cell membrane, therefore relevant white blood cells cannot recognise and destroy the infected cells
TB evasion mechanisms
- once engulfed by phagocytes in the lungs, the bacteria produces substances that will prevent a lysosome from fusing with the phagocytic vacuole
- this prevents the bacteria from being broken down by digestive enzymes, leaving them to multiply within the phagocytes
- the bacteria can disrupt anitgen presentation in infected phagocytes, therefore the immune system cannot recognise and destroy them
describe the role of DNA primers in the production of amplified DNA
- primers have a specific base sequence
- these bind to complementary bases at either end of the amplified DNA
- thus, providing a site for the DNA polymerase to bind
explain why amplified DNA fragments would be different from a wild allele
- base sequence of the alleles are different
- the restriction enzyme cuts at a specific site
- that is only present in the amplified allele
- therefore, a shorter fragment is produced for the amplified allele
Describe the changes that occur inside a body in the first week after death
- body temp falls
- rigor mortis
- break down of cells by enzymes in the body
- bloating
describe the role of decomposers in the carbon cycle
- decomposers break down organic material and respire releasing co2 into the atmosophere
what are the three main stages of the PCR reaction and what temps are required
- denaturation: 95 degrees
- annealing: 50-60 degrees
- elongation/extension - 72 degrees
what are microsatellites
short non-coding repetitive sequences present throughout the chromosome
pathogen definition
any organisms which causes disease. includes bacteria, viruses, protoctists and fungi
bacterial cell structure
- single celled prokaryotic organisms
circular chromosomal DNA: floats free in cytoplasm
ribosomes: 70s and smaller than eukaryotic cells
cell wall: made of muerin (glycoprotein)
pili: used to communicate with other cells
mesosomes
plasmids: small, circular rings of DNA
slime capsule
flagellum
how does HIV replication occur
- If a person with HIV exchanges bodily fluid with another person, HIV can infect the second individual and will be present in their bloodstream.
- the HIV virus uses its attachment proteins to enter T helper cells by binding to receptors on the T cell.
- the capsid is released into the cell where it breaks apart to release the RNA and enzymes. The enzyme reverse transcriptase converts the RNA into DNA.
- the single-stranded DNA is converted into double-stranded DNA which the enzyme integrase can insert into the DNA of the T cell.
- The T cell now has the ‘instructions’ (genes) to produce viral proteins.
- The viral DNA is transcribed and translated and the viral proteins are used to build new virus particles, which move out of the T cell and infect other cells.
HIV structure
- core of RNA and enzymes (reverse transcriptase and integrase)
- enclosed in a protein coat called a capsid
- surrounding the capsid is an envelope which contains attachment proteins
specific immune response definition
- happens after the non specific immune response
- aimed at a particular antigen
- involves the activation of two types of immune cells: T lymphocytes and B lymphocytes
PCR definition
technique used to amplify fragments of DNA
what needs to be added before PCR is carried out
- DNA sample
- free DNA nucleotides
- primers
- DNA polymerase
explain the three stages of PCR
1, separation of the DNA strands: mixture is heated to 95 which causes H bonds to break between the DNA strands
2. annealing of the primer: mixture is cooled to 60 which allows the primer to anneal to the DNA
3. DNA synthesis: temp is increased to 72 which is optimum temp for DNA polymerase. DNA polymerase forms a new DNA strand from catalysing the formation of phosphodiester bonds between the free DNA nucleotides which align along the DNA template strand by complementary base pairing
- 30-40 cycles of PCR are carried out. each cycle doubles thee amount of DNA
what are fluorescent tags and why are they added
- So that the DNA can be visualised, we add a fluorescent molecule which binds to the DNA and makes it visible when exposed to UV light.
- A common fluorescent tag is ethidium bromide, which inserts itself between the DNA bases and gives off fluorescence under UV light.
what is electrophoresis
- separates the DNA fragments according to length after they have been amplified and stained with a fluorescent dye
- It works because DNA is negatively charged, which means it will move towards a positive charge when placed in an electric field.
- Shorter DNA fragments travel through the gel more quickly, which means they will travel a longer distance
four steps of gel electrophoresis
- restriction enzymes are used to cut DNA into fragments.
An agarose gel is prepared which contains a row of wells at the top of the gel. The gel is placed into a tank containing buffer solution which is able to conduct electricity. - The DNA sample is mixed with a loading dye - this turns the DNA mixture a dark colour and helps you see what you’re doing. A fixed volume of the DNA samples are pipetted into the wells.
- An electrical current is passed through the gel and the DNA will begin to move towards the bottom of the gel (towards the anode).
- Once the dye has reached the bottom, the electricity is turned off and the banding pattern is visualised under UV light.
suggest how an ‘evolutionary race’ between virus’s and their host could affect the bodys specific immune response
- mutation has occurred in the nucleic acid
- change in antigens on the virus surface
- antibodies can no longer bind to the virus
- secondary immune response will not be possible
state four conditions of a peat bog that allow the remains of bodies to be well preserved
- lack of oxygen: denies access to microorganisms to respire body molecules aerobically
- acidic soil: takes decomposers’ enzymes below their optimum pH so they are unable to feed on the body
- low temperature: takes decomposers’ enzymes below their optimum temperature so their activity is low
- permanently wet soil: water which is always anaerobic, prevents access of oxygen from the air to the body’s tissues
explain the stages of rigor mortis
(Lack of oxygen) means muscles begin to respire anaerobically
Lactic acid is produced, lowering the pH / making the muscles acidic
This low pH denatures enzymes
(So) no ATP is produced
Myosin heads stay attached to actin filaments
Stiffness of muscles is the result
explain the importance of decomposition to ecosystems
To ensure ecosystems are not full of dead plants/animals; [1 mark]
To recycle chemical atoms/elements / there is only a finite supply of atoms from which matter can be made; [1 mark]
other than CO2, name one other carbon containing product of decomposition emitted into the atmosphere by saprophytic micro-organisms
methane
what is the role of a DNA primer in PCR
Provide a double stranded section of DNA for the enzyme to bind to
Define the region to be amplified
PCR involves an enzyme…
how is this enzyme suitable for a role in PCR
It joins together free DNA nucleotides to make new DNA strands
It is extracted from bacteria that are thermophilic / live in very hot environments
It can withstand high temperatures / does not denature at high temperatures
state three applications of the PCR reaction
- identifying pathogens
- Amplifying DNA samples during ancestry/paternity testing
- Amplifying DNA found at a crime scene for DNA fingerprinting
state two features that allow nucleic acids or proteins to be separated by gel electrophoresis
- net overall charge
- size of fragments
which component of DNA gives it its charge
phosphate groups
which class of enzymes can be used to cleave DNA into fragments prior to gel electrophoresis
restriction enzymes
why would researchers use PCR
Because only small amounts of DNA were obtained / available
To amplify specific sequences of DNA e.g. for DNA profiling
why would DNA profiles be the exact same
twins
phagocytosis leads to presentation of its antigens…state where the anitgens would be presented
on the cell membrane
antibiotics are safe to use in humans as they do not block processes such as DNA replication. why are these processes not inhibited in humans but can be in bacteria
Antibiotics block specific processes that occur within prokaryotic cells but not in eukaryotic cells
how do T cells and B cells work together for effective combat of infectious disease
T cells bind to the antigen (on the antigen presenting cells/pathogen)
T (killer) cells combat the infection that has entered host cells
T helper cells signal to help activate B cells
T (killer) cells kill infected cells;
B cells combat infection in the liquid phase/body fluids eg. in blood plasma
B (plasma) cells secrete antibodies (that lead to phagocytosis)
Both form memory cells to remain in the blood and protect against future infection (by that antigen)
how do Y shaped antibodies cause pathogens to agglutinate
explain the consequences of aggluniation to the pathogen
- One antibody can bind to (antigens on) two separate pathogen cells
- Holding the pathogens together
- Pathogen cells become held/clumped together by multiple antigen-antibody complexes between cells
- pathogens are tightly clumped so cannot exchange food with their surroundings
- and so metabolic processes stop and the cells die
- the clump of dead cells can be removed by phagocytosis
retrovirus definition
- can make DNA from RNA
- has RNA coding for the enzyme reverse transcriptase
describe the steps by which HIV can lead to death caused by a bacterium
- HIV enters T helper cells and releases its rna
- the t helper cells machinery is taken over and reverse transcriptase synthesises viral DNA
- new viral components are synthesized and viruses released, destroying the T-cell
- B cells no longer get activated
- so an opportunistic infection can take hold
give one reason why a patient who is developing AIDS is likely to suffer from infections of increasing severity
- T helper cells are killed off gradually
- t cell helper count drops below a critical level
- viral DNA replicated by the HIV viruses may take a long time to become fully active
compare and contrast the primary and secondary immune response
comparisons:
- both are activated by an antigen
- both give rise to memory cells that remain in the blood circulation
contrasts
- Primary - time taken for plasma cells to develop and multiply WHEREAS in secondary response, plasma cells multiply quickly
- Primary - the patient is more likely to suffer symptoms WHEREAS secondary, patient will be unaware of being infected / be asymptomatic
Devise an investigation to determine the optimum number of cycles for the polymerase chain reaction
- use dna polymerase in excess
- change the number of cycles each time the PCR is carried out
- use gel electrophoresis to determine the quantity of DNA produced
- choose the smallest number of cycles that produces an observable band
explain the effect of temperature on the rate of growth of maggots
- temp affects enzymes
- which increases kinetic energy
- leading to more frequent collisions between enzyme and substrate
how do microorganisms in the soil break down stems
- stems contain cellulose or starch
- enzymes are secreted by the microorganisms
- which break down glycosidic bonds
- forming monomers of glucose which are soluble
- soluble molecules soak into the ground/are taken up by organisms
what type of chemical reaction takes place in decomposition
hydrolysis
how can dna profiles be compared after gel electrophoresis
- comparing total number of bands
- comparing position of bands
- comparing width/size of bands
what affects temp of dead bodys
- body size
- fat level
- position of the body
how do HIV particles enter T helper cells
- glycoproteins on the surface of the virus bind to receptors on the surface of the t helper cells
- viral envelope then fuses with cell membrane of the t helper cell
- viral RNA enters the cell
Explain why the destruction of T helper cells causes the symptoms of AIDS.
- lack of t helper cells reduces cytokine production
- therefore reducing activation of B cells
- reducing antibody production
- leading to an increased risk of opportunistic infections
which cell produces antibodies
plasma cell
Explain why the presence of microorganisms on the skin and in the gut helps to
prevent pathogenic organisms multiplying in the body
- flora in the gut and skin are better adapted to the conditions
- thus can outcompete pathogenic organisms
- bacteria in the gut secrete chemicals which help to destroy pathogens
explain the role of t cells in a person who is infected by a virus for which they have been vaccinated
- vaccinated person will have t memory cells
- the t memory cells will recognise antigens specific to the virus
- t helper cells activate b cells and t killer cells
- t killer cells destroy cells infected with the virus
why are there few species of bacteria in the stomach
- ph is too low for the enzymes of most bacteria to function
- bacteria that live in the stomach have adaptations that enable them to survive
give two differences between the genetic material of bacteria and viruses
- bacteria have DNA, viruses have DNA or RNA
- bacteria have circular DNA, viruses have linear DNA
- bacterial DNA is double stranded, viral DNA is single stranded
how do macrophages ingest bacteria
- phagocytosis
Describe how the production and action of interferon differs from the production and
action of lysozyme.
- interferon is involved in viral infections, lysozyme affects bacteria
- interferon produced by infected cells, lysozyme present in phagocytes
- interferons inhibit replication of viruses, lysozyme kills bacteria
practical for investigating different types of antibiotics
- set up sterile work area by wiping surfaces with disinfectant and setting up a bunsen burner
- transfer some bacterial culture on to an agar plate using a sterile pipette and spread it out using a sterile spreader
- Soak similar sized paper discs in different types of antibiotics
- Add a negative control to the investigation by soaking a disc in distilled water
5.Space the discs apart on the agar plate using sterile forceps - Lightly tape a lid onto the petri dish, invert and incubate at 25 °C for 24 to 48 hours
- Bacteria will grow to form a ‘lawn’ on top of the agar
Any clear patches in the lawn will indicate where bacteria could not grow -this is called the clear zone
