Download lab6 A

Lab. No. 6A
Gram’s Stain
Gram’s +ve
Cocci
Bacilli
Gram’s -ve
Cocci
Rods
Gram +ve Bacilli
Spore forming
Non spore forming
Anaerobic
Aerobic
Clostridium
Bacillus
Corynebacterium
 Most
Important species:
 Cl.
tetani → causes tetanus.
 Cl. perfringens → causes gas gangrene.
 Cl. botulinum → causes food poisoning
(botulism).
Gram’s +ve, spore forming bacilli
(the position of the spores
helps in species
identification).
Drum-Stick appearance of Cl.tetani
These organisms require
anaerobic cultivation
which can be achieved through:
1- Removal of O2& replacing it with an
inert gas→ Blood agar plates in
Anaerobic Jar.
2- Special anaerobic media
containing a reducing agent.
1. Anaerobic jar:
2. Anaerobic media:


Thioglycollate broth.
Cooked meat medium.
1-Thioglycollate broth:

It is a nutrient broth which serves as
anaerobic medium due to presence of
1- Sodium thioglycollate which acts as a
reducing agent.
2- Small amount of agar to increase viscosity
of the medium thus decreasing convection
current.

The medium contains Redox
“oxidationreduction potential” indicator
(Methylene Blue) which changes color of the
medium when 30% of the medium becomes
oxidized.
Thioglycolate broth:
It should be prepared in long tube
O2
aerobic bacteria
anaerobic bacteria
2- Cooked meat medium:
It is anaerobic medium due to presence of:
 Meat particles (prepared from heart
muscles) which contain hematin and
glutathione that act as reducing agents.
Reactions on Cooked meat medium:
1.Saccharolytic reaction:
 Causes fermentation of the muscle
glycogen with production of acid and gas.
 The meat particles remain intact.
e.g. Cl.perfringes.
2. Proteolytic reaction:
 Causes digestion of the meat particles leading
to formation of black, foul smelling sulphur
compounds.
Litmus
milk medium:
It Contains:
• Skimmed milk (without fat)
i.e: contains only sugar (Lactose)
and protein (casine)
• Litmus indicator (acid base and
redox indicator).
Reactions
on Litmus milk medium:
1. Acidic reaction:
Lactose
(milk sugar)
Fermentation
acid
Litmus indicator
pink colour
2. Alkaline reaction:
Digestion
Casine
(milk protein)
Litmus indicator
Alkaline amines
Blue colour
3. Stormy Clot Formation:
(Lactose)
milk sugar
(Casine)
milk protein
Fermentation
acid
Coagulation
+
clot
gas
Stormy
clot