Medical Oral Microbiology Topic A - 01
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Diagnostic of staphylococci
Task 1: Microscopy of infectious material
Observe preparation stained by Gram staining. Draw and describe your observations. Look
for bacteria (their shape, colour and quantity), WBC and epithelia. Use immersion oil and
immersion objective.
Task 2: Microscopy of microbial cultures
Stain according to Gram pure cultures of prepared microorganisms. Draw your observations.
Use immerion oil and immersion objective.
Task 3: Growth on Blood Agar
Describe morphology of colonies of prepared bacterial strains on Blood Agar. Note colour
and haemolytic properties of observed colonies.
No. of strain Description of colony (size, colour, shape, surface, margins, haemolysis)
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Task 4: Growth of bacteria on blood agar supplemented with 10% NaCl
Evaluate the growing abilities of prepared strains on the Blood Agar supplemented with 10%
NaCl, which is selective growing medium for staphylococci.
On Blood Agar supplemented with 10% NaCl grow strains:..................
Task 5: Catalase test
Show presence of enzyme catalase in observed strains. Take a loop of colony and submerge it
into drop of 3% H2O2 on a microscopy glass. Write down the reaction in your strains.
No. of strain Reaction Interpretation
On the basis of tasks 2 - 5 choose strains, which belong to the genus Staphylococcus:
........................ In the next tasks find out which staphylococci are here:...........
Task 6: Plasmocoagulase test
Into 0,5 ml 10x diluted rabbit plasma was suspended several colonies of examined strain of
staphylococcus. The Suspension was incubated in 37 °C. The results are obtained after 1, 2
and 24 hours. Positive reaction is coagulation of rabbit plasma in the test tube, i.e. gelatination
of the whole amount of rabbit plasma. Write down and draw the results after 24 hrs of
incubation.
Positive: Negative:
Task 7: Proof of hyaluronidase
On the blood agar we inoculate 1 cm wide line of Streptococcus equi, bacterium, which
produces large capsule with presence of hyaluronic acid. To this line we inoculate line with
examined strain of staphylococcus. If examined strain produces hyaluronidase, diffuses to the
surrounding area and causes lysis of capsules of Str. equi. This can be seen as semicircle in
Medical Oral Microbiology Topic A - 01
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the slimy line of Str. equi. Draw result of reaction (including positive and negative control)
and describe.
Strains of staphylococci were determined to be:
Task 8: Susceptibility of staphylococci to antibiotics
Examine susceptibility of your strains of staphylococci to selected antibiotics on the basis of
disk diffusion test. The susceptibility evaluate by comparing diameter of inhibition zone with
the break-point zone of the antibiotics.
S. aureus S. epidermidis
Antibiotic Zone diameter
(mm)
Intepretation
Zone diameter
(mm)
Intepretation
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Check-up questions:
1. What are important characteristics of staphylococci (metabolic, morphologic and growth
propertis)?
2. How to distinguish between S. aureus and so-called coagulase-negative staphylococci?
S. aureus coagulase-negative staphylococci
3. Which infections caused by members of genus Staphylococcus you can meet in dentistry?
4. Which are the most important anti-staphylococcal antibiotics?
5. What is the MRSA and which complications in therapy it brings?