MYP Agar Base

EMD Cat. No. 1.05267.0500
500 g


Medium proposed by MOSSEL et al. (1967) for the enumeration, detection and isolation of Bacillus cereus in foodstuffs.

The German Regulations for Dietetic Foodstuffs (Verordnung über diätetische Lebensmittel (Diätverordnung)) stipulate that foodstuffs should be tested for Bacillus cereus. The medium furthermore complies with the German DIN-Norm 10198 for the investigation of milk and food and to the requirements acc. to § 35 LMBG (00.00/25) and 01.00/53) for the investigation of food.

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


Mode of Action
 This culture medium is highly adapted to the properties of Bac. cereus.
a)
 		Bac. cereus is mannitol-negative. The mannitol content of the medium thus allows differentiation of the accompanying mannitol-positive microbial flora which are identified by a change in color of the indicator phenol red to yellow.
b)
 		Bac. cereus is not affected by concentrations of polymyxin which inhibit the common accompanying microbial flora (DONOVAN 1958). Addition of polymyxin is necessary, however, if the sample material is suspected to contain high numbers of accompanying microorganisms.
c)
 		Bac. cereus produces lecithinase. The insoluble degradation products of egg-yolk lecithin accumulate around the Cereus colonies to form a white precipitate. A lecithinase reaction occurs very early in many strains, Cereus colonies can, therefore, often be rapidly identified before accompanying polymyxin-resistant microorganisms have had a chance to fully develop.


Typical Composition (g/liter)
 Peptone from casein 10.0; meat extract 1.0; D(-)mannitol 10.0; sodium chloride 10.0; phenol red 0.025; agar-agar 12.0
 Also to be added (per liter of medium):
 egg-yolk emulsion 100 ml; polymyxin B sulfate 100,000 IU = Bacillus cereus Selective Supplement.

Preparation
Suspend 21.5 g in 450 ml purified water, autoclave (15 min at 121°C).
Cool to about 45 to 50°C, add 50 ml (this volume can be varied depending on the degree of turbidity desired) of sterile egg-yolk emulsion and the contents of 1 vial Bacillus cereus Selective Supplement, mix. Pour plates.
pH: 7.2 ± 0.2 at 25 °C.
The plates (incl. egg-yolk) are evenly turbid and slightly orange (red without egg-yolk).

Experimental Procedure and Evaluation
 Inoculate the plates by spreading the sample on the surface of the medium.
Incubation: 18-40 hours at 32°C.
Bac. cereus appears as rough, dry colonies with a pink to purple base which are surrounded by a ring of dense precipitate. Colonies surrounded by a yellow or a clear zone are not Bacillus cereus. Further tests should be performed to confirm the identity of Bacillus cereus (anaerobic degradation of D(+)glucose, degradation of gelatin, positive nitrate reduction) (BROWN et al. 1958).

Quality control (spiral plating method)

Test strains
 Inoculum
 (cfu/ml)
 		Recovery
 rate (%)
 		Colony color
 		Precipitate
Bacillus cereus ATCC 11778
 		10³-105
 		40
 		red
 		+
Bacillus cereus var. mycoides
 		10³-105
 		40
 		red
 		+
Bacillus subtilis ATCC 6051
 		10³-105
 		40
 		yellow / pink
 		+
Escherichia coli ATCC 11775
 		10³-105
 		0.01
 		-
Pseudomonas aeruginosa ATCC 25668
 		> 105
 		0.01
 		-
Proteus mirabilis ATCC 29906
 		> 105
 		Not limited!
 		red
 		-
Staphylococcus aureus ATCC 6538-P
 		10³-105
 		Not limited!
 		yellow
 		+


Additives
 
EMD Cat. No. Product Pack Size
1.03784.0001 Egg-yolk emulsion sterile 10 x 100 ml
1.09875.0001 Bacillus cereus Selective Supplement (Polymyxin B; 50,000 IU) 16 vials


Literature

BROWN, E.R., MOODY, M.D., TREECE, E.L., a. SMITH, C.W.: Differenzial diagnosis of Bacillus cereus, Bacillus anthracis and Bacillus cereus var. mycoides. J. Bact., 75; 499-509 (1958).
 DONOVAN, K.O.: A selective medium for Bacillus cereus in milk. J. Appl. Bact., 21; 100-103; (1958).
 INAL, T.; Vergleichende Untersuchungen über die Selektivmedien zum qualitativen und quantitativen Nachweis von Bacillus cereus in Lebensmitteln.
I. Mitteilung. Fleischwirtsch. 51; 1629-1632 (1971).
 IV. Mitteilung. Fleischwirtsch. 52; 1160-1162 (1972).
 Bundesgesundheitsamt: Amtliche Sammlung von Untersuchungsverfahren nach § 35 LMBG. Beuth Verlag Berlin, Köln.
 DIN Deutsches Institut für Normierung e.V.: DIN 10198 Teil 1 und 2.
 MOSSEL, D.A.A., KOOPMANN, M.J., a. JONGERIUS, E.: Enumeration of Bacillus cereus in foods. Appl. Microbiol., 15; 650-653 (1967).
 NYGREN: Phospholipase C-producing bacteria and food poisoning. An experimental study on Clostridium perfringens and Bacillus cereus. Acta path. microbiol. scand., 56; Suppl. 1-160 (1962).


Bacillus cereus, Staphylococcus aureus