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A selective medium for staphylococci and streptococci.

Code: CM0331

Directions
Add 39g to 1 litre of distilled water. Boil to dissolve and sterilise by autoclaving at 121°C for 15 minutes.

Code: SR0070

Directions
Reconstitute one vial as directed aseptically add the contents to 500 ml of Columbia Agar Base containing 5-7% Defibrinated Horse Blood SR0050 cooled to approximately 50°C. Mix well and pour into sterile Petri dishes.

Description
A selective medium for Staphylococci and Streptococci of the type described by Ellner¹ and subsequently named Columbia CNA Agar can be made by adding Oxoid Staph/Strep supplement to Columbia Agar Blood Base.Columbia CNA Agar can thus be prepared quickly and conveniently as and when required. Because the antibiotics contained in the supplement are freezedried they always show optimal activity at the time of use.
The supplemented Columbia Agar is inhibitory to S. albus and Micrococcus species as well as Gram-positive and Gram-negative rods. It suppresses
growth of Proteus, Klebsiella and Pseudomonas species while permitting unrestricted growth of S. aureus, haemolytic streptococci and enterococci.
Phenylethyl alcohol medium by comparison frequently permits growth of Proteus and Klebsiella species as well as showing a marked attenuation of
the growth of Gram-positive cocci.
Staph/Strep Supplement enables important Gram-positive cocci to be recognised more readily and isolated easily from the mixed bacterial populations
contained in many clinical specimens and foods.

Technique
The medium is inoculated in the normal way and incubated aerobically at 35°C for 18 hours.
DO NOT INCUBATE IN CO2.

Storage conditions and Shelf life
Store the dehydrated medium below 10-30°C and use before the expiry date on the label.
Store the prepared medium at 2-8°C.

Appearance
Dehydrated Medium: Straw coloured, free-flowing powder.
Prepared medium: Opaque red-coloured gel.

Quality control

* This organism is available as a Culti-Loop®

Precautions
Incubation in a CO2-enriched atmosphere will cause inhibition of staphylococcal growth². If it is necessary to incubate plates in such an atmosphere then Staph/Strep Supplement should not be used.
All suspected staphylococcal and streptococcal colonies should be further investigated to confirm their identity. The Staphylase Test DR0595 and the
Streptococcal Grouping Kit DR0585 are useful for these purposes.

References
1. Ellner P. D., Stoessel C. J., Drakeford E. and Vasi F. (1966) Tech. Bul. Reg. Med. Technol. 36. No. 3.
2. Morton C. E. G. and Holt H. A. (1989) Med. Lab. Sci. 46. 72-73.