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Antibiotics

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Antibiotics
Antibiotics
Noadswood Science, 2011
Friday, April 8, 2016
Antibiotics
 To understand how antibiotics work and the advantages and
disadvantages associated with them
Antibiotics
 Antibiotics are substances that kill bacteria or stop their growth
(often targeting the bacteria’s cell capsule)
 They do not work against viruses – it is difficult to develop drugs
that kill viruses without also damaging the body’s tissues
Antibiotics
Antibiotic
Target
Penicillin
Breaks down cell walls
Erythromycin
Inhibits protein synthesis
Neomycin
Inhibits protein synthesis
Vancomycin
Inhibits protein synthesis
Ciprofloxacin
Inhibits DNA replication
Penicillin
 The first antibiotic (penicillin) was discovered in 1928 by Alexander
Fleming
 He noticed that some bacteria he had left in a petri dish had been
killed by naturally occurring penicillium mould
 Since the discovery of penicillin,
many other antibiotics have been
discovered or developed – most
antibiotics used in medicine have
been altered chemically to make
them more effective and safer for
humans
Resistance
 Bacterial strains can develop resistance to antibiotics, due to
natural selection
 In a large population of bacteria, there may be some cells that
are not affected by the antibiotic – these cells survive and
reproduce, producing even more bacteria that are not affected
by the antibiotic
 MRSA (methicillin-resistant staphylococcus aureus) – it is very
dangerous because it is resistant to most antibiotics
 It is important to avoid over-use of antibiotics, so we can slow
down, or stop, the development of other strains of resistant
bacteria
Resistance
 Although vaccinations and antibiotics are useful in the fight against
pathogens, bacteria and virii can mutate to form a new resistant
‘strains’...
Bacteria
1. Variation – some strains of bacteria
are resistant
2. Competition – the non-resistant
bacteria are killed by the penicillin
3. Survival of the fittest – the resistant
bacteria survive
Antibiotic
4. Reproduction – the resistant bacteria
reproduce and pass on their
adaptations to their offspring
Bacterial Growth
 Using the agar plates spread bacteria evenly over them
 Place some antibiotic disks randomly onto the culture (ensure
you note which antibiotic plate is which)!
 Which antibiotic is the best?
A
 Which antibiotic are the bacteria
most resistant to?
B
C
D
E
Bacterial Growth
 Using discs on agar covered with bacteria – this technique is
used in hospitals on samples of urine, blood and stools to
work out which antibiotic to use
 The antibiotic disc which has the
caused the widest circle in the
bacterial plate is the best for that
type of bacteria – it has killed the
highest quantity of bacteria (C)
A
B
C
D
E
 The antibiotic which the bacteria
are most resistant too has the
smallest circle (B)
Cleanliness
 One simple way to reduce the risk of infection is to maintain
personal hygiene and to keep hospitals clean
 In the 19th century Semmelweis realised the importance of
cleanliness in hospitals – however, although his ideas were
successful, they were ignored at the time because people did not
know that diseases were caused by pathogens that could be killed
MRSA – Research
 How can we control the spread of antibiotic resistant bacteria in
hospitals?
 Could we stop using antibiotics – why / why not?
Defence
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