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Material Safety Data Sheet

Required Products

Organisms

Organisms in the Clinical sector this product works with:

Dehydrated Culture Media

Sector: Clinical

CEFIXIME RHAMNOSE SORBITOL MACCONKEY AGAR
(CR-SMAC Agar Base)

Code: CM1005

A selective, differential medium based on Sorbitol MacConkey Agar with added rhamnose and cefixime. This medium provides a selective base with improved differentiation of Escherichia coli O157.

Typical Formula*

gm/litre

Peptone

20.0

Sorbitol

10.0

Bile Salts No. 3

1.5

Sodium chloride

5.0

Rhamnose

5.0

Neutral red

0.03

Crystal violet

0.001

Agar

15.0

pH 7.1 ± 0.2 @ 25°C

* Adjusted as required to meet performance standards 

CEFIXIME SUPPLEMENT

Code: SR0191

Vial Contents (each vial is sufficient for 500ml of medium)

per vial
per litre

Cefixime

0.025mg

0.05mg

Directions
Suspend 28.25g in 500ml of distilled water. Mix well and sterilise by autoclaving at 121°C for 15 minutes. Cool to approximately 50°C and aseptically add the contents of one vial of Cefixime Supplement SR0191, reconstituted as directed. Mix well and pour into sterile Petri dishes.
To reconstitute Cefixime Supplement, aseptically add 2ml sterile distilled water to 1 vial of supplement. Mix gently to dissolve.

Description
The addition of rhamnose to Sorbitol MacConkey Agar (SMAC) has been shown to aid the differentiation of Escherichia coli O157 from background flora. Approximately 60% of non-sorbitol fermenting Escherichia coli of serogroups other than O157 ferment rhamnose (Sheffield PHL, unpublished data). Cefixime has been shown to reduce the level of competing flora, particularly Proteus spp., that often account for large numbers of non-sorbitol fermenting colonies1.

Escherichia coli O157 do not usually ferment sorbitol or rhamnose, so will appear as straw coloured colonies. However, rhamnose is fermented by most sorbitol negative Escherichia coli of other serogroups. These colonies will be pink/red and will not be counted as presumptive Escherichia coli O157 colonies1.

Cefixime Rhamnose Sorbitol MacConkey Agar (CR-SMAC) is a selective and differential medium for the detection of Escherichia coli O157. Field trials have shown that using CR-SMAC, in conjunction with the more selective CT-SMAC, leads to a higher overall recovery of Escherichia coli O157 from enrichment broths2,3.

Technique
Inoculate the plates with a suspension of the sample. to produce separated colonies. Incubate for 24 hours at 35-37°C.

Examine the plates for straw coloured colonies; these are sorbitol and rhamnose negative organisms. Confirm suspected Escherichia coli O157 with the E. coli O157 Latex Test DR0620 or Dryspot E. coli O157 DR0120.

Coloured colonies may also occur:

sorbitol positive

pink to red

rhamnose positive

pink to red

Storage conditions and Shelf Life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium for up to 2 weeks at 2-8°C.

Appearance
Dehydrated medium: Straw pink coloured, free-flowing powder
Prepared medium: Red coloured gel

Quality control

Positive control:

Expected results

Escherichia coli O157:H7 NCTC 12900 *
(sorbitol negative, rhamnose negative)

Good growth, straw coloured colonies

Negative controls:

 
Escherichia coli ATCC® 25922 *
(sorbitol positive)
Good growth, pink colonies

Proteus mirabilis ATCC® 29906
(sorbitol negative, rhamnose negative)

Inhibited

* This organism is available as a Culti-Loop®

References
1.
Chapman, P.A., Siddons, C. A., Zadik, P. M. and Jewes L. (1991) J. Med. Microbiol. 35:107-110
2. Information on file at Oxoid.
3. Wallace, J. S. and Jones, K. (1996) J. App. Bacteriology 81:663-668

 
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