Microbiology study question (University of Adelaide) for mid-semester test
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Vet Sc 3512RW (VET_SC_3512RW)
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University Of Adelaide (AU
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Veterinary Microbiology and Microbial Disease
This is a completed study question from DT with correct answers. Use this instead of wasting time to write your own. All the exam questions will be drawn from this. If you study this completely you can garantee yourself a HD or full marks. This is for the mid semester exam (Also check for next docu...
LEARNING OBJECTIVES:
● Gain an appreciation of the contribution of founding scientists to the field of
microbiology
● List the four principles underlying Koch's postulates for a pathogenic
organism
● Identify the major bacterial structures associated with pathogenesis in animal
infections
● Recall the cell wall structure of bacteria Gram positive and Gram negatives
REVISION QUESTIONS:
1) What are Koch’s postulates for a pathogenic organism (4 marks)? Give an
example of a pathogenic bacteria for which Koch’s postulates cannot strictly be
fulfilled (1 mark).
1. That agent must be present in every case of the disease
2. That agent must be isolated and cultured in vitro
3. The disease must be reproduced when a pure culture of the agent is inoculated
into a susceptible host
4. The agent must be recoverable from the experimentally-infected host
Bacteria such as Mycobacterium tuberculosis causes latent infections,
which organisms exposed to it may not reproduce the disease (tuberculosis).
which does not fulfil Koch’s third postulate - can’t be grown in pure culture medium
2) Explain the contribution to bacteriology of the following eminent scientists.
a. Robert Koch (5 marks)
- Develop pure culture technique
- Develop solid media which allow the isolation of individual bacterial colonies
to discover the cause of anthrax, tuberculosis and cholera
- Proposed Koch’s Postulates for a pathogenic organism
b. Louie Pasteur (5 marks).
- Disprove the Spontaneous Generation Theory and develop the Germ Theory.
- Develops the basis of fermentation, brewing and pasteurization
- Study contagious disease like rabies, fowl cholera and anthrax
- Has early work for vaccination
c. Joseph Lister (5 marks)
- Develop the concept of antiseptics with carbolic acid as well as sterilization
with Pasteur
- First isolation of bacteria by souring of milk.
3) Outline the major differences between prokaryotes and eukaryotes (5 marks)
1. DNA of eukaryotes is bound to protein, linear and has introns
2. Eukaryotes has membrane bounded organelles and 80S ribosome (vs 70S)
3. Eukaryotes reproduce by mitosis and meiosis with paired chromosomes;
4. Eukaryotes have larger average sizes
,4) What are the three major groups of bacteria (3 marks)? Give an example of a
species of bacteria in each group (2 marks).
1. Gracilicutes (gram -ve cell wall), Escherichia coli
2. Firmicutes (gram +ve cell wall), Staphylococcus aureus
3. Tenericutes (lacking a cell wall), Mycoplasma hyopneumoniae
5) Describe how you would set your microscope to view unstained bacteria using
the x 10 and x40 (high, dry) lenses (2 marks) followed by Gram-stained bacteria
using the oil immersion (x 100) lens (2 marks). What is the minimum size of
objects that can be resolved at x 1000 (1 mark)?
Power source -> Mount specimen onto the stage -> adjust to the lowest objective lens
(5x) -> Look into the eyepiece and slowly rotate the coarse adjustment knob from the
bottom (clockwise) to bring specimen to focus -> Adjust condenser for appropriate
(maximum) amount of light & move specimen to the centre of field -> slowly rotate
the fine adjustment knob to obtain a clearer image of specimen -> switch to the x10
objective and re-adjust the focus with the fine adjustment knob -> proceed to the x40
objective once it is focused
Take out the unstained specimen -> mount the gram-stained one onto the stage ->
Repeat the above steps -> add one drop of immersion oil onto the slide add Before
further proceeding to the x100 lens -> Examine the lens: it should almost touch the
slide and the oil should fill the space between the slide and the lens. While looking
through the eyepiece, use only fine adjustment knob to move the lens up and
down;focus
Minimum:100x. Bacteria range: 0.2um to 2um.
6) Outline by means of a diagram the major differences between the
Gram-positive and the Gram-negative bacterial cell wall (3 marks). How does
this determine whether the organism stains purple or red (2 marks)?
1. Peptidoglycan cell wall in gram positive bacteria is thicker
2. Gram negative bacteria is bounded by outer membrane with LPS (need to draw!!)
but not in gram positive bacteria
Crystal violet is retained in the thick peptidoglycan cell wall in gram positive bacteria
despite depolarization so it is stained blue, but not retained in the one in
gram-negative (thin) so it is stained red.
7) What components make up the structure of lipopolysaccharide (LPS) (3
marks). Describe the biological properties of two components of LPS (2 marks)?
Lipid A (hydrophobic glycolipid), core oligosaccharide, and O antigen (both
hydrophilic)
Lipid A is the toxic component of endotoxin and a potent stimulator of the immune
system.
O-antigen is responsible for antigenic variation.
,8) What is the structure of bacterial peptidoglycan (3 marks)? What properties
does it impart to the bacterial cell wall (1 mark)? Describe in simple terms how
beta-lactam antibiotics cause lysis of peptidoglycan (1 mark).
It is made up of sugars and amino acids, and when many molecules of peptidoglycan
joined together, they form an orderly crystal lattice structure.
Cross-linking between amino acids in the layer of peptidoglycan forms a strong
mesh-like structure that provides shape of the organism.
β-Lactam antibiotics interfere with the synthesis of peptidoglycan, cannot produce
cell walls and are termed L forms.
9) Describe the structure and importance to pathogenic bacteria of the following
(5 marks):
a. Flagella
- Occurs in both gram +ve and -ve (Eg Streptococcus equi, Bacillus anthracis,
Yersinia pestis, Pasteurella multocida);
Structure:
- Filamentous structure (often longer than bacteria)
Importance:
- For chemotaxis and motility in most bacteria, by changing direction (rotate
counter clockwise, not flex)
- It is antigenic (H-antigens) which triggers immune response.
b. Fimbriae (or pili)
- Occur exclusively in gram -ve (except Corynebacterium renale)
- Fimbriae are host specific (not zoonotic)
Structure and importance:
1. Short, abundant pili for adhesion. Attachment = virulence factor
2. Long, Sparse (sex pilus) for conjugation, = transfer of virulence genes.
c. Capsule (or glycocalyx)
- Occur in both gram +ve and -ve
- Slime layer can be easily removed but capsule is more adherent
- Hyaluronic acid (polysaccharide + protein)
Importance:
- attachment, resisting phagocytosis, and protection from desiccation
13) What are bacterial spores (2 marks)? Describe the functions and morphology
of bacterial spores (2 marks). Name a bacterial genus that forms spores (1 mark).
Bacterial spores/endospores contain DNA and thick cell layers which remain dormant
(resistant to environmental stress). It can acquire plasmids and become pathogenic.
Variety of morphologie - terminal, subterminal, or even larger than the cell
Bacillus anthracis, Clostridium tetani
, LECTURE 2: GROWTH AND NUTRITION OF BACTERIA
READING: QUINN (2011) CHAPTER 8 pp123-128
LEARNING OBJECTIVES:
● Distinguish between batch and continuous culture and discuss their uses
applicable to veterinary science (eg vaccine production)
● Define the conditions required for bacterial growth in vitro in liquid and on
solid media and the techniques used to isolate, subculture and preserve
bacteria
● Define the differences between routine, enrichment, selective and differential
agar as they apply to veterinary microbiology
● Recall the four phases of the bacterial growth curve in vitro (liquid media) and
distinguish between total and viable counts and the methods used to determine
each.
REVISION QUESTIONS:
1) How you would determine the number of viable bacteria in a bacterial
suspension (5 marks)?
By Colony counting in the spread plate.
It follows serial ten-fold dilution of a bacterial suspension. (Have a look at 點計)
A fixed volume of each dilution is spread on the surface of agar plates and incubated
for 24-48hrs.
Colony counts are carried out on plates with 30-300 colonies after incubation.
The number of viable bacteria in the suspension is calculated and expressed as
colony-forming units (CFU)/mL of suspension. (Have a look at 點計)
2) Explain the differences between the following types of bacteriological media (5
marks)
Routine/General Purpose/Basal Media
- Simple media that support the growth of most non-fastidious
- Can be solid/liquid, containing nutrients (C and N sources), cofactors, pH
buffers and serum requirements
Enrichment media
- Addition of extra nutrient in the form of blood, serum, egg yolk etc. to basal
medium
- Used to grow nutritionally exacting (fastidious) bacteria
- Or when organism needed is in low numbers or swamped by others
Selective media
- To augment growth of desirable bacteria and inhibit unwanted commercial or
contaminating bacteria
- (Only allow specific type of bacteria growing on it eg S. aureus can grow on
MSA, not for S. epidermis. Because pathogenic aureus ferment mannitol to
acid. Which is indicated by pH indicator)
Differential media
- Bacteria are identified by colony color, so to distinguish closely related ones
- Eg blood agar: general nutrients w/ 5% sheep blood - determine haemolytic
capabilities eg different Streptococcus carrying out different type of
haemolysis
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