Corynebacterium & Bacillus - Microscopic appearance - Colonial morphology.
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Transcript of Corynebacterium & Bacillus - Microscopic appearance - Colonial morphology.
Corynebacterium diphtheriae
- Gram positive pleomorphic, long, thin, and curved forms can be seen and also short rods and rods enlarged at one end (clubshaped).
- C. diphtheriae often appears beaded due to the
presence
of dark staining granules in the rods.
-These granules, known as volutin or metachromatic
granules, are energy-storing inorganic
polyphosphate
units. In some strains the granules form at the ends
of
the rods.
- The granules are most numerous after the organism
has
been cultured on a protein-rich medium such as
Dorset
egg or Loeffler serum.
Albert Staining of volutin granules
Albert Staining of volutin granules
1- Fix the dried smear using alcohol.
2- Cover the smear with the toluidine blue
malachite green stain for 3–5 minutes.
3-Wash off the stain with clean water.
4- Tip off all the water.
Albert Staining of volutin granules
5- Cover the smear with Albert’s iodine for
1 minute. Wash off with water.
6- Wipe the back of the slide clean, and place it
in
a draining rack for the smear to air-dry.
7- Examine the smear microscopically to look
for
bacteria containing metachromatic granules
Albert Staining of volutin granules
Bacteria cells . . . . . . . . . . . . . . . . . . . . . . Pale green
Metachromatic granules . . . . . . . . . . . . Green-black
B. anthracis is a high risk infectious
pathogen, therefore handle specimens
and infected material with care, wearing
protective gloves and face mask, and
following recommended safety
procedures.
large, 5–8 X 1.5 μm, Gram positive, non-motile bacillus, often appearing joined end to end in chains
In smear from Specimens:- Bacilli are capsulated. The capsular material often appears irregular and
fragmented
In smears from aerobic cultures: Bacilli are non-capsulated
but contain oval spores (same diameter as the bacilli), giving the
organisms a beaded appearance.
They occur in chains.
Fixation of smears:-
B. anthracis is not killed by heat-fixation.
Smears should be chemically fixed by
immersing the dry smears in a container
of potassium permanganate solution for
10–15 minutes.
Bacillus anthracis
Blood agar:- large grey-white 2-5 mm in diameter
irregular with wavy edges colonies (non or slightly
haemolytic).
Bacillus cereus
- Food poisoning.
- Opportunistic infections in
immunocompromised
persons (bacteraemia, pnumonia and
wound
infection).
Bacillus cereus
Blood agar:- large grey-white 2-5 mm in diameter
irregular with wavy edges haemolytic colonies.