Transcript Can HIV and TB be treated?

Are there Treatments for AIDS
and TB?
Specification
 16 Discuss how the theory of an ‘evolutionary race’ between pathogens and
 their hosts is supported by the evasion mechanisms as shown by Human
 Immunodeficiency Virus (HIV) and Mycobacterium tuberculosis (TB).
 17 Distinguish between bacteriostatic and bactericidal antibiotics.
 18 Describe how to investigate the effect of different antibiotics on
 bacteria.
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19 Describe how an understanding of the contributory causes of hospital
acquired infections have led to codes of practice relating to antibiotic
prescription and hospital practice relating to infection prevention and
control.
Treating AIDS
 Treating AIDS – antiretroviral drugs – 4 types –
http://www.youtube.com/watch?v=RO8MP3wMvqg&feature=player_embedded
 Watch and write down what the 4 different drugs do
 Reverse transcriptase inhibitors
 Protease inhibitors
 Integrase inhibitors
 Fusion Inhibitors
 HIV can develop resistance to these drugs. Suggest how.
Treating Tuberculosis
 Where did the antibiotic for Tuberculosis come from? What is it called?
 Streptomyces griseus from a sick chicken – produced antibiotic called
streptomycin
 Q6.42: Give any disadvantages and any advantages of all options to reach a
conclusion. Hint: Topic 1: What makes a good study?
 Option 1:
 Adv: Doctors don’t have to turn anyone down until antibiotic runs out
 Disadv: Not double blind, not a random sample
 Option 2:
 Adv: Random sample
 Disadv: NOT double blind
 Option 3:
 Adv: Can be double blind reducing bias if placebo is given to half the group,
random sample
 Disadv: are the case and control group matching?
Two classes of antibiotics
How do antibiotics work?
 Q 6.43
 Activity 6.15
 How can bacterial growth be inhibited?
 Inhibition of specific enzymes found in the bacterial cell but
not in the host: Explain how this is possible.
 Inhibition of bacterial cell wall synthesis leading to lysis.
Explain how this leads to lysis.
 Disruption of cell membrane leading to lysis. Explain how
this could lead to lysis.
 Inhibition of nucleic acid synthesis, replication and
transcription. How does this interfere with cell growth and
multiplication?
 Inhibition of protein synthesis. How could this affect the
cell?
 Q 6.44
 Activity 6.16: Classifying Antibiotics
Evolutionary Race
 Read pages 131-133
 In the context of infectious disease who is in this
race?
 What is the selection pressure exerted on humans?
 What is the selection pressure exerted on the
pathogens?
 Which group can evolve more rapidly? (for why see
next slide)
Why do we still have diseases like TB?
 Which three factors affect the speed a population evolves and adapts
to a changing environment? For each explain how and why.
 Reproductive rate:
 The faster it is the faster a population can adapt to new conditions. Bacteria
reproduce extremely rapidly. Increases chances of mutations occuring.
 Size of the gene pool:
 the greater it is the faster a population can adapt to new conditions because
more different alleles (new ones brought in by mutations) are present
increasing the chances of one being advantagous in the new conditions
 Strength of the selection pressure:
 The stronger it is the faster a population can adapt to new conditions. Our
immune system is the selection pressure for pathogens-
 Give an example of a characteristic that could be advantageous to a
pathogen in the evolutionary race?
 Mutation resulting in a change in shape of the antigen. Antibodies and
receptors of B cells and T cells no longer fit so useless in reacting to
this pathogen
We are not winning the race.
 What changed in this evolutionary race between host
and bacteria since the late 1970s?
 Use of antibiotics
 Why is TB still far from being eradicated?
 Antibiotics are the new selection pressure
 Explain how antibiotic resistant mycobacterium
tuberculosis have developed.
 Hint: Natural selection and conjugation
 Activity 6.17 TB and Macrophages
Why are hospitals such «dangerous»
places?
 What are multiple-resistant bacteria?
 What are HCAIs?
 What are hospitals doing to combat this? Explain each measure.
 Hand wash stations at the entrance to every ward- with
disinfectant
 Doctors and nurses are not allowed to wear ties, watches or long
sleaves- less places pathogens could be and make contact with
wounds accidently.
 Antibiotics are used only when needed (not to treat viral infections
or just in case)
 Patients must complet treatment even when they feel better so all
of the specific pathogenic bacteria are killed. None can survive to
pass on their resistance allele.
Activity 6.15a: Questions
 Read the worksheet Activity 6.15: Which Antibiotic is most
effective and answer Questions 1-3 on page 2. Then complete the
following questions.
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 What is the aim of the experiment?
 To determine which antibiotic is most effective against a specific type
of bacteria.
 What is the purpose of carrying out such an experiment?
 In order to determine which antibiotic should be used for treating a
specific infection.
 Identify the independent variable.
 Type of antibiotic.
Activity 6.15a: Questions
 Find examples of aseptic technique and explain the
importance of these techniques.
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washing hand with antibacterial soap
disinfectant spray
sterilised by flaming/ autoclaved forceps
rising lid only/ not off completely
petri dishes sterile (autoclaved)
Importance: to avoid contamination by other microbes
 What is the purpose of the agar in the Petri dishes?
 To provide a source of nutrients, water and a surface to grow on
Activity 6.15a: Questions
 Why should you not seal the Petri dish completely?
 To allow O2 in to avoid the growth of anaerobic strains of bacteria
which may be pathogenic
 How long should the sample be incubated for?
 48 hours
 Why is it important not to open the plate after incubation?
 To prevent infection of people doing the experiment or to prevent
contamination of the plates
 What is the dependent variable and how would you measure it?
 Diameter of clear zone around disk, using a ruler, in mm
Activity 6.15a: Questions
 What should you do to ensure that your results are valid?
 Same species of bacteria
 Same volume and concentration of antibiotic solutions
 same incubation temp and time
 Same diameter and type of disks
 Same type of nutrient agar
 Repeat and take mean
Activity 6.15a: Questions
 How could you be sure that your results are accurate?
 Use graduated pipette to measure volumes
 Using a ruler to measure the diameter of the clear zone at the widest point in
several dishes and calculate a mean area. r= d/2, A= π r 2
 Using a ruler to measure the diameter across different point of one clear area and
calculate the mean diameter. r= d/2, A= π r 2
 Lay a piece of graph paper over it. Estimate the number of graph squares covered
 Aseptic technique to reduce contamination
 Use incubator to control temperature
 How would you display your results?
 Table:
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first column: type of antibiotic,
Second column: diameter of clear zone (mm) for 3 trials
Third column: mean (mm)
 Graph: bar chart, x axis: type of antibiotic, y axis: diameter of clear zone
Limitations
 Growth of unwanted microbes
 Accurate measurement of area of inhibition- odd
shapes, not a perfect circle
 Contamination of controls
 Age of antibiotic can affect its effectiveness
 Placing of discs evenly on the Petri dish
 Using wrong species of bacteria- unaffected by these
extracts