IV. INVESTIGATION OF C. DZPHTHERZAE
159
As basal agar, a plain agar prepared from fresh meat infusion was also
tried with good results instead of using beef extract.
After being poured into plates, the medium must be transparent, and
hay-yellow in colour. Tinsdale plates should not be used more than 48 h
after preparation. During this interval plates should be stored at + 4°C.
They have to be dried for 5-10 min in the incubator, with the lid halfopen, before inoculation.
Commercial Tinsdale base and commercial dried enrichment medium
are available (Difco).
Each lot of medium whether commercial or self prepared, is checked
with control reference strains for growth and production of a satisfactory
strong brown halo around the C . diphtheriae colonies.
3 . Blood agar medium ( B A )
ally with 10 ml defibrinated sheep blood and poured in Petri dishes.
Nutrient agar (90 ml) melted and cooled at 45-50°C is mixed asepticThe medium may be stored at 4°C for 7 days.
On BA C . diphtheriae presents pearl-greyish colonies with granular
C . ulcerans is very similar to C . diphtheriae with smooth yellowish, dense
Atypical corynebacteria grow with very rough colonies having white,
surfaces.
colonies.
silverish or deep yellow colonies.
4. C T B A (cystine-tellurite-blood agar) plates
(a) To 100 ml of melted nutrient agar, pH 74-7.6 at 45"C, add sterile:
10 ml defibrinated sheep blood
4 ml potassium tellurite, 1% solution
0.1 ml L-cystine, from a 1% solution
(b) Potassium tellurite 1% solution
1 g potassium tellurite (Merck)
100 ml distilled water
Dissolved by heating and autoclaved for 20 mic at 105°C.
(c) L-Cystine 1% solution is obtained by first dissolving 1 g anhydrous
sodium carbonate in 10 ml distilled water; after heating to boiling point,
add 1 g L-cystine. Warm again and stir well while adding 90 ml distilled water. Autoclave 20 min at 105°C. The solution is kept in the dark
in brown flasks at + 4°C. Care must be taken not to use a solution for more
than 1 month. If it changes colour from light yellow it should be discarded.
159
As basal agar, a plain agar prepared from fresh meat infusion was also
tried with good results instead of using beef extract.
After being poured into plates, the medium must be transparent, and
hay-yellow in colour. Tinsdale plates should not be used more than 48 h
after preparation. During this interval plates should be stored at + 4°C.
They have to be dried for 5-10 min in the incubator, with the lid halfopen, before inoculation.
Commercial Tinsdale base and commercial dried enrichment medium
are available (Difco).
Each lot of medium whether commercial or self prepared, is checked
with control reference strains for growth and production of a satisfactory
strong brown halo around the C . diphtheriae colonies.
3 . Blood agar medium ( B A )
ally with 10 ml defibrinated sheep blood and poured in Petri dishes.
Nutrient agar (90 ml) melted and cooled at 45-50°C is mixed asepticThe medium may be stored at 4°C for 7 days.
On BA C . diphtheriae presents pearl-greyish colonies with granular
C . ulcerans is very similar to C . diphtheriae with smooth yellowish, dense
Atypical corynebacteria grow with very rough colonies having white,
surfaces.
colonies.
silverish or deep yellow colonies.
4. C T B A (cystine-tellurite-blood agar) plates
(a) To 100 ml of melted nutrient agar, pH 74-7.6 at 45"C, add sterile:
10 ml defibrinated sheep blood
4 ml potassium tellurite, 1% solution
0.1 ml L-cystine, from a 1% solution
(b) Potassium tellurite 1% solution
1 g potassium tellurite (Merck)
100 ml distilled water
Dissolved by heating and autoclaved for 20 mic at 105°C.
(c) L-Cystine 1% solution is obtained by first dissolving 1 g anhydrous
sodium carbonate in 10 ml distilled water; after heating to boiling point,
add 1 g L-cystine. Warm again and stir well while adding 90 ml distilled water. Autoclave 20 min at 105°C. The solution is kept in the dark
in brown flasks at + 4°C. Care must be taken not to use a solution for more
than 1 month. If it changes colour from light yellow it should be discarded.