Assessment task: Investigation
Antibiotics to the rescue … not always!
Read the background information then answer the questions that follow.
Background information:
On Monday afternoon, Justin went to the emergency
department at his local hospital following a fall he had
while skateboarding with his mates after school.
Fortunately, he had only sprained a finger but did
suffer some bruising and cuts to his legs. After
spending several hours in the emergency department
having his wounds cleaned, stitched and bandaged,
Justin went home.
On Tuesday morning, one of the deeper cuts on Justin’s leg was red and felt
warm when touched. His mother thought it might be infected and looked in the
medicine chest. She found some antibiotics that had been prescribed for him 2
months earlier for a throat infection. He hadn’t finished the antibiotics so
thinking that it might help, she suggested that he take one – which he did.
Throughout Tuesday, the cut on Justin’s leg became
increasingly red, swollen and painful. He was feeling
quite sick and when he came home from school, his
mother decided to take him back to the emergency
department that night. The cut had become badly
infected.
The doctor cleaned and restitched his leg and
prescribed a daily dose of antibiotic A, a stronger
version of the same antibiotic Justin had taken at
home that morning.
By Thursday, Justin’s infection had spread to the point where it was too painful
to walk. In addition to this, he had become very sick. His mother took him back
to the hospital where they admitted him immediately. The doctors administered
a different kind of medication, antibiotic C, directly into his bloodstream via an
intravenous drip.
On Friday morning, Justin was feeling better and his leg had become less
painful and swollen. Unfortunately by Saturday, Justin took another turn for the
worse. The infection on his leg continued to spread, and he had a high
temperature. The medical staff involved with Justin’s case held an emergency
meeting to plan the next step of his treatment.
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Answer the following questions:
1.
Treating an infection with antibiotics is a standard practice. Why do you
think Justin’s infection is not responding to treatment?
2.
What information is required by the medical staff to treat Justin’s infection
successfully?
3.
It is common practice in some hospitals to take samples of fluids and tissue
from wounds treated with particular antibiotics so studies can be done –
should treatment not go to plan. Fortunately, samples had been taken each
time Justin had visited the hospital. Cultures of bacteria from each sample
were grown and the results recorded.
As a control, three cultures were also prepared and the results were
graphed.
Control plates were used by growing 10 000 (104) bacteria (of the type that
Justin was suspected of having) on an agar plate under known conditions. The
growth rate over 24 hours was measured and the results recorded.
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Figure 1: Results for the control plate cultures
Graph 1: No antibiotics
Graph 2: Antibiotics and
bacteria known to be
killed by this antibiotic
Graph 3: Bacteria
developing resistance
to antibiotic
Courtesy of WGBH-TV Boston, © 2010 WGBH Educational Foundation and Vulcan
Productions, Inc.
Variation exists in most populations. In bacterial
populations variation exists in their resistance to
antibiotics. This means that some bacteria are resistant
where some are more susceptible to antibiotics. While
an antibiotic will kill most bacteria in a population, some
will be resistant and survive. These live and continue to
reproduce – and pass their resistance on. This is an
example of natural selection.
4.
Explain the differences you can see between the three control graphs.
Graph 1:
Graph 2:
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Graph 3:
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Now examine the results of the bacterial samples taken from Justin. Each
Graph shows bacterial growth when the samples were exposed to four
antibiotics over six days. Each sample originally contained approximately 10
000 (104) of Justin’s bacteria. Hour 0 represents the number of bacteria in
Justin’s tissue samples at the time the sample was taken.
Figure 2: Results for Justin’s sample cultures
Monday 5 pm (arrival at the
hospital).
Monday 9 pm (before leaving
hospital
(no
antibiotics yet
Tuesday (6 pm)
Thursday night (5 pm)
(on return to hospital Justin had
taken antibiotic A and the
doctors had prescribed a new
dose of antibiotic A.)
(after returning and being
admitted, Justin had been
taking antibiotic A since
Tuesday morning.
Doctors prescribe antibiotic C.)
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Saturday morning (Justin had
spent Friday in hospital, having
taken antibiotic A since
Tuesday and antibiotic C since
Thursday.)
Courtesy of WGBH-TV Boston, © 2010 WGBH Educational Foundation and Vulcan
Productions, Inc.
Using the information provided answer the following questions. Wherever
possible, use evidence from the data to support your answers:
1.
From the graphed results, can you conclude that there were any antibioticresistant bacteria present in Justin’s tissue samples taken when he arrived
at the hospital on Monday?
2.
Which antibiotics were the bacteria resistant to by Saturday?
3.
At what point did the population of bacteria show resistance to:
antibiotic A: ___________________________
antibiotic B: ___________________________
antibiotic C: ___________________________
antibiotic D: ___________________________
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4.
Explain why the number of bacteria is so different between Monday 5 pm
and Tuesday after growing in the presence of antibiotic A.
5.
Explain why the number of bacteria is so different on Thursday compared
to Saturday after growing in the presence of antibiotic C.
6.
Which antibiotic is the most suitable for treating Justin’s infection?
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