WILKINS-CHALGREN ANAEROBE AGAR

Code: CM0619

A medium for the general growth of anaerobes, recommended for antimicrobial susceptibility testing. See Antimicrobial Susceptibility Testing Section for details of the use of this medium in AST methodology.

Typical Formula*	gm/litre
Tryptone	10.0
Gelatin peptone	10.0
Yeast extract	5.0
Glucose	1.0
Sodium chloride	5.0
L-Arginine	1.0
Sodium pyruvate	1.0
Menadione	0.0005
Haemin	0.005
Agar	10.0
pH 7.1 ± 0.2 @ 25°C

* Adjusted as required to meet performance standards

Directions
Suspend 43g in 1 litre of distilled water. Bring to the boil to dissolve completely. Sterilise by autoclaving at 121°C for 15 minutes.

Description
Recognising the need for a standard medium for antimicrobial susceptibility testing of anaerobic bacteria, Wilkins and Chalgren¹ developed a new medium which would not require the addition of blood. Their formulation included yeast extract to supply vitamins and other growth factors such as purines and pyrimidines, that are necessary for good growth of Peptostreptococcus anaerobius and Prevotella melaninogenica. Arginine was added to ensure sufficient amino acid was available for the growth of Eubacterium lentum. Pyruvate was added as an energy source, for asaccharolytic cocci such as Veillonella². It also acts similarly to catalase and degrades traces of hydrogen peroxide, which may be produced by the action of molecular oxygen on medium constituents and interfere with the metabolism of anaerobes³. Haemin was found to be essential for the growth of Bacteroides species⁴ and menadione for Prevotella melaninogenica⁵.

Peptones derived from the single protein sources casein and gelatin, were used to improve standardisation of the medium. Wilkins and Chalgren¹ considered that this medium consistently grew anaerobes as well or better than media such as Brucella Agar or Schaedler Anaerobe Agar. A collaborative study in ten laboratories showed that it could be used in an agar dilution method for susceptibility testing of anaerobic bacteria and recommended a procedure as a reference method ⁶.

The value of such a procedure was further confirmed by Brown and Waatti⁷, who found that the incidence of resistance of anaerobic bacteria to frequently used antibiotics had increased. They considered it essential that diagnostic laboratories should have the capability of carrying out susceptibility tests on anaerobic bacteria.

Wilkins-Chalgren Agar (CM0619) has been recommended for the susceptibility testing of anaerobic bacteria using the Receiver Operating Characteristic (ROC) procedure.

Wilkins-Chalgren Anaerobe Agar is also recommended for the isolation of anaerobic organisms from clinical specimens. It has been shown to function well both in Petri dishes and roll tubes. (B.S. Drasar, personal communication).