COLUMBIA CNA AGAR BASE

A medium for the isolation of Gram-positive cocci.

Code: CB1/3612

Typical formula g/l

Peptocomplex	10.0
Tryptose	10.0
Peptone	3.0
Maize starch	1.0
Sodium chloride	5.0
Agar	2.0
Nalidixic acid	15 mg
Colistin	10 mg

pH: 7.3 +/- 0.2

Directions

Suspend 41 g in 1000 ml of cold distilled water. Heat to boiling and sterilise in the autoclave at 121^{_{°C for 15 minutes. Cool to 50°C and add 5% of defibrinated blood.}}

_Description

_{Columbia CNA Agar Base is prepared with the same formula as Columbia Agar Base, with the addition of 10mg/litre of Colistin and 15mg/litre of Nalidixic Acid to inhibit the growth of Gram-negative bacteria. The medium is used with the addition of 5% defibrinated blood to isolate Gram-positive cocci and to demonstrate their haemolytic properties.}

_{Quality assurance (Columbia CNA Blood Agar Base + 5% def.blood) (37°C-24 h)}

_{Productivity control}

_{S.pyogenes ATCC 19615: good growth, β haemolysis}

_{S.pneumoniae ATCC 6305: good growth, α haemolysis}

_{S.aureus ATCC 25923: good growth}

_{Selectivity control}

_{P.mirabilis ATCC 12453: partially inhibited}

_Storage

_{Dehydrated media: 15-30°C}

_{User prepared plates: 1 month at 2-8°C}

_Reference

_{Quality Assurance for Commercially prepared Microbiological Culture Media-2nd ed.; Approved Standard. 1996.}