MacCONKEY Sorbitol Agar (SMAC)

EMD Cat. No. 1.09207.0500
500 g


Selective Agar for the direct isolation and differentiation of enterohemorrhagic (EHEC) E. coli O157:H7-strains from foodstuffs and other materials.

The culture medium complies with the requirements of the DIN Norm 10167 for the detection of Escherichia coli (E. coli) serotype O157:H7 in foods as well as with the methods of FDA-BAM for the isolation of enterohemorrhagic E. coli (EHEC).


Additives


EMD Cat. No. Product Pack Size
1.09202.0001 CT-Supplement 1 x 16 vials
1.09205.0500 mTSB Broth with Novobiocin 500 g
1.14582.0500 mEC Broth with Novobiocin 500 g



Mode of Action Preparation
Experimental Procedure and Evaluation Quality Control
Typical Composition (g/liter) Literature
Picture/Image  


Mode of Action
 Bile salts mixture and crystal violet largely inhibit the growth of the Gram-positive microbial flora. The addition of Cefixime Potassium tellurite (CT) Supplement increases the selectivity for E. coli O157:H7 and suppresses the remaining accompanying flora. For the detection of E. coli O157:H7 the CT-SMAC Agar method is superior to the HC Agar (SZABO) method according to the study of WEAGANT (1995).
 Sorbitol, together with the pH indicator neutral red, is used to detect sorbitol-positive colonies and turning them red in color. Sorbitol-negative strains, on the other hand, form colorless colonies.
Preparation
 Suspend 51.5 g in 1 liter of purified water, autoclave (15 min at 121 °C), pour plates.
 pH: 7.1 ± 0.2 at 25 °C.
 The plates are clear and red and are stable for up to 6 months when stored at +2-8 °C.
Preparation of CT-SMAC Agar
 Suspend 25.8 g in 500 ml of purified water, autoclave (15 min at 121 °C).
Dissolve the lyophilisate of one CT Supplement  (Cat. No. 1.09202.) in the original vial by adding about 1 ml of sterile distilled water.
 Mix gently and add the contents to the sterile, still liquid SMAC Agar cooled below 50 °C. Pour plates.
 pH: 7.1 ± 0.2 at 25 °C.
 The plates are clear and red and are stable for up to 6 months when stored at +2-8 °C.
Experimental Procedure and Evaluation
 Inoculate 25 g of the food sample in 225 ml mEC broth or mTSB broth and incubate for 18-24 h at 35-37 °C aerobically.
 Approximately 0.1 ml of the broth is then streaked on the surface of SMAC Agar or CT-SMAC Agar in such a way to obtain well isolated single colonies.
 Incubation: 18 to 24 h at 37 °C.

Quality control

Test strains
 Recovery rate
 %
 		Colony color
 		Sorbitol
E. coli O157:H7 ATCC 35150
 		70
 		colorless
 		-
E. coli ATCC 11775
 		70
 		red
 		+
Serratia marcescens ATCC 14756
 		70
 		red
 		+
Bacillus cereus ATCC 11778
 		0.01


Typical Composition (g/liter)
 Peptone 20.0; sodium chloride 5.0; bile salts No. 3 1.5; sorbitol 10.0; crystal violet 0.001; neutral red 0.03; agar-agar 15.0.
Literature

DIN Deutsches Institut für Normung e.V.: Nachweis von Escherichia coli O157 in Lebensmitteln. - DIN 10167.
 FDA Bacteriological Analytical Manual, 8th Edition 1995, Chapter 4. Escherichia coli and the Coliform Bacteria, page 4.20: Isolation Methods for Enterohemorrhagic E. coli (EHEC).
 WEAGANT, S.D., J.L. BRYANT, and K.G. JINNEMAN, An improved rapid technique for isolation of Escherichia coli O157:H7 from foods. - J. Food Prot., 58; 7-12 (1995).
 ZADIK, P.M., P.A. CHAPMAN, and C.A. SIDDONS, Use of tellurite for the selection of verocytotoxigenic Escherichia coli O157. - J. Med. Microbiol., 39; 155-158 (1993).


E.coli O157:H7

E.coli O157:H7, E.coli, Serratia marcescens



© 2002 Merck KGaA, Darmstadt, Germany