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9.7 Option- Pharmaceuticals: 4. Penicillin fights bacteria
Extract from Senior Science Stage 6 Syllabus (Amended
October 2002) © Board of Studies, NSW.
[Edit: 19Sep 08].
Prior Learning: Science Stages 4-5 Syllabus: Outcome 4.8 (content 4.8.3a and b),
Background: Before our current understanding of bacteria and diseases caused by them, people died regularly from simple infections. The discovery of penicillin and the people involved in this discovery and development to commercial production is a fascinating story.
gather, process and present information from secondary sources to trace the historical development of our understanding of disease caused by bacteria including the contributions of two of:
- Lister
- Pasteur
- Koch
- You can gather information on the
above from
Important Early Microbiologists
Ohio State
University, Mansfield, Ohio, USA. - Add to this information by looking in encyclopedias and medical books.
- Process the information by assessing the reliability of the information from different sources. Make sure you make notes on the Historical development of our understanding of the disease and the person’s involvement in that understanding. Remember you only need to research two people.
- You could present your information in appropriate text types. Use diagrams or photographs of people with symptoms of the diseases in your presentation.
identify different types of bacteria based on shape
- cocci
- bacilli
- spirilla
-
Bacteria can be classified according to their shape as
observed with the light microscope:
- Cocci: spherical (coccoid)
- Bacilli: rod shaped
- Spirilla: spiral shaped.
Descriptions and diagrams of bacterial shapes can be found in junior and
senior biology texts e.g Haire et al, Core Science Bk 3
p 55 and you can find information at Kingdom Monera:
The Procaryotes .
Scroll down till you reach The many shapes of
bacteria. BIL 161 Evolution and Biodiversity Information
Center, USA.
outline the structure of bacteria to identify
- cell membrane
- cell wall
- cytoplasm
- Knowledge of bacterial structure is necessary to
explain the mode of action of penicillin and other
antibiotics.
- Bacteria are simple cells that do not have a true
nucleus.
- The bacterial cell membrane is a thin film that allows
nutrients and mineral substances in and waste products out.
- The cell wall gives bacteria their structural rigidity
that protects them from attack by other agents.
- The cytoplasm is a jelly-like substance within the cell that is encased by the membrane. All the biochemical reactions necessary for the cells existence and reproduction take place there.
Bacterial
Cell Structure : Cells Alive, Quill Graphics, USA
plan, choose equipment and resources for, analyse the risk, implement appropriate procedures for and perform a first-hand investigation to culture bacteria present in our surroundings and relate the growth rate to environmental conditions of temperature
- An introduction to the techniques of cell culture can be found at How
To Culture Bacteria in the Laboratory , Summer Research Program for Science
Teachers, Ayorinde Ayetiwa, Washington Irving High School, Colombia University, New York,
USA.
- More detailed methodology is given on the Web
site How to Streak
a Bacterial Culture About.com, USA
- When you have decided which technique to use you will need to plan
your investigation, taking into consideration the equipment
that is available. The lab assistant will have a recipe for the agar and will
prepare plates for inoculating if you ask her/him.
- You will need to work out which bacteria to use and how to obtain it. Leaving
a plate exposed to the air for five minutes should produce a harmless bacteria.
Another place to obtain harmless bacteria could be a culture like yoghurt.
- When growing bacteria, you must analyse the risk of someone
being infected who handles the plates. A much lower risk will occur if you
use non-disease causing bacteria. Whatever is used you still should implement
procedures that will minimize any cross infection. Talk to your teacher
about the procedures to use.
- Perform the investigation. Be aware that if you are going to relate the growth rate to temperature you will need to have the bacteria growing in different temperatures. Decide, after research, which temperatures are appropriate.
outline the process of reproduction in bacteria by fission
- When bacteria reach a certain size they divide by
binary fission. Binary fission means to split into two.
This happens by the bacterial chromosome making a copy of
itself. These copies then attach to different parts of the
cell membrane. The cell membrane and cell wall then grows
producing a long bacteria. When it has reached its maximum
length new membrane and cell wall grow across the cell and
then the cell splits to form two cells. When it does this
there is an identical chromosome in each new cell.
- The products of this division are two similar daughter
cells from the parent bacterium. These daughter cells in
turn divide to produce another two cells.
- The division process continues until a colony of bacteria is produced.
Information on cells and cell division can be found at
Introduction to bacteria
Science in the Real World, Microbes in Action, University
of Missouri, St Louis, Missouri, USA.
Scroll down to
Growth.
gather, process and present information from secondary sources to identify the rate of reproduction of different bacteria
- Gather information from various
sources such as text books, journals and the Internet. When
using the Internet use a search engine and use words such
as ‘rate’, ‘bacteria’,
‘reproduction’, ‘growth’. To get
the rates for different bacteria use the name of a specific
bacteria such as E. coli and/or Helicobacter pylori.
- Process the information by organizing
it in such a way that the different bacteria can be
compared easily. Make sure it is just the different species
and not other factors such as temperature that has caused
the different rates.
- To present the information use texts and graphs in a clear way such as on an overhead transparency.
Useful information
The rate of reproduction of bacteria is demonstrated by their population growth curve.
Bacteria grow most rapidly in the exponential or logarithmic growth phase when their numbers double during each generation time.
Generation time or doubling time is the time between the formation of a new bacterium and its division into two new daughter cells. Generation time is a characteristic of the species of bacterium.
Information,
graphics and real-time pictures of bacteria growing .
Cells Alive, James A Sullivan, Quill Graphics, USA.
identify conditions that determine the rate of reproduction of bacteria and explain their effects
- Environmental conditions affect the rate of
reproduction of bacteria both in nature and under
laboratory conditions.
- In nature, bacterial reproduction is affected by
temperature, pH (acidity), availability of nutrients,
oxygen, water and the presence of competing organisms.
The number of bacteria will therefore vary as these
conditions change with environmental conditions.
- Under favorable conditions bacteria cultures will continue to grow until they run out of nutrients and are poisoned by their own waste products.
gather, process and present information to discuss the circumstances surrounding the identification of the substance produced by the fungus, Penicillium notatum, which appeared to inhibit the growth of bacteria
- Gather information from a range of
resources.
- When you have enough information from different sources process the information by assessing its reliability by comparing the information. If there is a discrepancy check one or even two other sources.
This source gives a very full account of the
discovery of penicillin .
Penicillin The Wonder Drug, Botany Department,
University of Hawai’i at Manoa, USA.
- Present your findings to the class in an appropriate format.
explain why penicillin only works on bacteria while they are reproducing by relating its effect to its action on the bacterial cell wall
- During reproduction and prior to the fission of the
bacterium into daughter cells, new cell wall material
must be made.
- The bacterial cell wall consists of polymers
(long chain molecules) that are cross-linked.
(Cross-linking strengthens polymers).
- Penicillin inhibits enzymes that cross-link the
polymers and thus weakens the newly forming cell wall.
- The weakened cell wall bursts releasing the cytoplasm
and the bacterium dies.
- Because penicillin affects the formation of new cell
wall material, it is only effective against bacteria that
are reproducing and will not affect formed cells.
- Penicillin will not affect body cells because they lack a cell wall; therefore penicillin selectively kills bacteria and not normal human or other animal cells.
assess the concern that bacteria have become resistant to penicillin and discuss possible implications for the future use of penicillin
- Some bacteria have mutated into penicillin-resistant species hence the diseases caused by them are no longer treatable with this antibiotic.
-
Bacteria have become resistant to penicillin because of
the following:
- over-prescription by physicians from patients demanding antibiotics for non-bacterial infections
- patients not taking all the tablets prescribed (completing the full script)
- release of excreted penicillin into sewers where large numbers of bacteria reside and have time to build up resistance
- use of antibiotics to improve the production of livestock.
- The future effectiveness of penicillin is in jeopardy because of the growing problem of resistance and efforts are being made to counter the problem by making semi-synthetic penicillins and drugs similar to penicillin.
The
problem of anti-biotic resistance is described.
Combating Antibiotic Resistance, USFDA.
A more recent article is
The scourge of antibiotic resistant bacteria by Laura H Kahn, Bulletin of
the Atomic Scientists, 2007.
Dr Peter Rutledge, an Australian scientist working on developing drugs to treat resistant infections spoke to NSW DET teachers in May, 2009. Click here then scroll down to his name and click on VIDEO to see his presentation on the Curriculum Directorate web site.
gather, process and present information from secondary sources to identify other antibiotics, their source, their mode of action and the bacteria they affect
- To gather information look on the Internet, in medical journals and in health books and journals. Only choose two or three other antibiotics and choose ones that have plenty of information about them.
- Process the information by sorting out what you need and discarding the rest. If the language is too difficult in the medical journal article you could check science journals like New Scientist. If information conflicts check a few more sources and use the information that is the same or similar in two or more sources.
- Present the information in a format that is suitable to the audience, eg on overhead transparency sheets if other students will be looking at it or in a booklet or folder. A table would be a good way to present the information and will ensure that each section has been covered. Use diagrams wherever possible.
Information on these drugs and their mode of action .
Antibiotics: Antibacterial Agents,
Kimball’s Biology Page, USA. This is a good site
for better students.
Useful information
Other commonly used antibiotics are the sulfa
drugs and the tetracyclines.
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