Description
General description
GranuCult® Mannitol egg yolk polymyxin agar (base) is used for the enumeration of Bacillus cereus. This medium contains two indicator systems, mannitol, and phenol red and egg yolk. Enzymatic digest of casein and meat extract provide carbon and nitrogen sources. The selective inhibitory component polymyxin suppresses the growth of many unwanted microorganisms. Bacteria that ferment mannitol to produce acids produce yellow staining of the medium with phenol red as a pH indicator. Bacillus cereus does not ferment mannitol so the medium around the colonies remains unchanged or is discolored due to light alkalization by forming pink colonies. The lecithin present in egg yolk is cleaved by the Bacillus cereus-lecithinase, which leads to the formation of an opalescent white precipitation zone surrounding the pink colonies. Bacillus anthracis, Bacillus mycoides, Bacillus pseudodomycoides, Bacillus thuringiensis, and Bacillus weihenstephanensis may not be distinguishable from Bacillus cereus on this medium.
Bacillus cereus Selective Supplement (1.09875) and Egg yolk emulsion (1.03784) are available to enhance selectivity and growth conditions.
Application
GranuCult® Mannitol egg yolk polymyxin agar (base) is used for the enumeration of presumptive Bacillus cereus from food and animal feed as well as from environmental samples and other materials.
Analysis Note
Appearance (clearness): clear to slightly opalescent
Appearance (color): red
pH-value (25 °C): 7.0 - 7.4
Growth promotion test in accordance with the current version of DIN EN ISO 11133.
Inoculum on reference medium (Bacillus cereus ATCC 11778 (WDCM 00001)):
Colony count (Bacillus cereus ATCC 11778 (WDCM 00001)):
Recovery on test medium (Bacillus cereus ATCC 11778 (WDCM 00001)): ≥ 50 %
Growth (Bacillus subtilis ATCC 6633 (WDCM 00003)): no limit
Growth (Escherichia coli ATCC 8739 (WDCM 00012)): total inhibition
Growth (Escherichia coli ATCC 25922 (WDCM 00013)): total inhibition
Colonies (Bacillus cereus ATCC 11778 (WDCM 00001)): pink colonies with precipitation halo
Colonies (Bacillus subtilis ATCC 6633 (WDCM 00003)): yellow colonies without precipitation halo
Incubation:
B.cereus 24 ± 3 to 44 ± 4 hours at 30 ± 1 °C
other teststrains 44 ± 4 hours at 30 ± 1 °C
A recovery rate of 50 % is equivalent to a productivity value of 0.5.
The indicated colony counts result from the sum of a triple determination.
Reference media: Tryptic Soy Agar
Legal Information
GRANUCULT is a registered trademark of Merck KGaA, Darmstadt, Germany
NutriSelect is a registered trademark of Merck KGaA, Darmstadt, Germany
Disclaimer
We offer two media types: the superior granulated GranuCult® and the cost-efficient powdered NutriSelect® culture media, depending on your needs. The designations basic, plus, or prime are added to indicate the quality control level, from basic quality control to standard QC plus to prime for full regulatory compliance.
