Summary :
◉ Overview
Brucella agar is a general purpose non-selective enriched medium for the cultivation of Brucella spp. and fastidious microorganisms in the laboratory.
With the addition of blood, Brucella agar is used to determine bacterial hemolytic reactions. The agar can also be used as a base for the isolation of Campylobacter spp.
Brucella agar
◉ Composition and Preparation of Brucella agar
Suspend the components, dehydrated powder, in water (43g in 1000ml of purified/distilled water). Bring to a boil and completely dissolve the medium and sterilize in an autoclave at 121°C for 15 minutes.
Cool the medium to 45°-50.0°C and aseptically add 5% red sheep blood or 10% horse blood. Distribute in
sterile Petri-dishes.
Composition Brucella agar |
|||
|---|---|---|---|
| Ingredients | gram/litre | ||
| Enzymatic digestion of casein | 10.0g/L | ||
| Enzymatic digestion of animal tissues | 10.0g/L | ||
| Yeast extract | 2.0g/L | ||
| Sodium Chloride | 5.0g/L | ||
| Dextrose | 1.0g/L | ||
| Sodium Bisulfite | 0.1g/L | ||
| Agar | 15,0 g/L | ||
◉ Principle and Interpretation
This medium promotes the growth of fastidious microorganisms thanks to its content of peptones, glucose, yeast extract and blood. Peptones provide organic nitrogen. Yeast extract is a powerful source of B vitamins. Glucose is used as an energy source. Horse blood provides both X and V factors which are necessary for the growth of certain organisms.
The growth of the accompanying microbial flora can be suppressed by the addition of bacitracin, polymyxin, cycloheximide and possibly ethyl violet.
The hemolytic reactions depend on the type of blood added
- Enterococci, which only very rarely haemolyze sheep blood, will produce a clearly visible beta-hemolysis in horse blood.
- Staphylococcus aureus, which is generally beta-hemolytic in sheep blood, will often be non-hemolytic in horse blood.
Different Brucella species can be differentiated by their different susceptibility to thionine and fuchsin dyes.