Simmons Citrate Agar | DM211D

Simmons Citrate Agar | DM211D

For the differentiation of the Enterobacteriaceae based on citrate utilisation.

MAST Simmons Citrate Agar can be regarded as a solidified form of Koser Citrate Medium (DM139), recommended for the differentiation of the Enterobacteriaceae.1-3 The basis of the medium originally proposed by Koser,4 was that faecal coliforms were unable to grow in a medium containing inorganic ammonium salts as the only source of nitrogen, with citrate as the sole carbon source. If large inocula were employed, the results in Koser's medium were difficult to elucidate and this prompted Simmons5 to develop a solid medium, obviating the disadvantage of turbidity as the growth indicator. As with Koser Citrate, care must be taken to exclude all extraneous sources of carbon and nitrogen such as cotton wool plugs etc.

Directions

1. Suspend by swirling 22.8g of powder in 1 litre or the contents of the sachet in the stated volume of distilled or deionised water.
2. Autoclave at 121ºC (15 p.s.i.) for 15 minutes.
3. Mix well before pouring.

Technical Formula

In Use

Inoculate the surface of the medium by streaking with a straight wire. If slopes are used, also stab the butt. Incubate for 48 hours at 37ºC.
Some members of the Salmonella, Klebsiella, Serratia and Citrobacter groups utilise citrate, as seen by their ability to grow and change the medium from green to blue.
Organisms such as E.coli, shigellae, S.typhi and S.paratyphi cannot utilise citrate as the sole carbon source and do not grow on the medium.