Enterobacteria Millichrome^™ plus Agar

The Enterobacteriaceae colonies form pink to red colonies after 24 h of incubation at an optimal growth temperature of 37°C, whereas the growth of E. coli forms blue colonies after incubation at the same temperature.

Enterobacteria Millichrome^™ plus Agar Base is a selective chromogenic culture medium intended for use in the qualitative direct detection, differentiation, and presumptive identification of Enterobacteriaceae in food industry

Enterobacteria Millichrome^™ plus Agar is a selective media for the detection and enumeration of Enterobacteriaceae. The use of this media allows for convenient distinguishing between E. coli and other Enterobacteriaceae spp. because of the distinct colors and clear background. This creates better contrast, aiding in differentiation. Additionally, the medium exhibits a high level of sensitivity and specificity, leading to an increased rate of detecting Enterobacteriaceae bacteria. Millichrome^™ chromogenic media is a specialized type of culture medium used to detect and isolate specific groups of bacteria based on their ability to produce enzymes with chromogenic substrates. Peptone and yeast extract provide nitrogenous nutrients and essential growth factors. Mineral salts maintain osmotic balance and supply necessary ions. The chromogenic and selective mix consists of substrates that change color when specific enzymes cleave them, along with agents that inhibit other organisms. The medium also contains growth factors to support the growth of Enterobacteriaceae bacteria. Finally, agar is included to solidify the medium.

Step 1 (Preparation of the mix)

• Disperse slowly 42.3 g of powder base in 1 L of purified water.
• Stir until agar is well thickened.
• Heat and bring to boil (100 °C) while swirling or stirring regularly.

Advice 1: For the 100 °C heating step, mixture may also be brought to a boil in a microwave oven: after initial boiling, remove from oven, stir gently, then return to oven for short repeated bursts of heating until complete fusion of the agar grains has taken place (large bubbles replacing foam).
DO NOT HEAT TO MORE THAN 100 °C. DO NOT AUTOCLAVE AT 121 °C.
Warning: If using an autoclave, do so without pressure.
Step 2 (Cooling)

• Cool in a water bath to 45-50 °C.
• Swirl or stir gently to homogenize.

Step 3 (Pouring in plates)

• Pour medium into Petri dishes.
• Let solidify.
• Let plates dry.

Store prepared media below 8°C, protected from direct light (max. 1 month) or 1 day at room temperature. Bottles can be stored for up to 6 months at 2-8°C.Store dehydrated powder, in a dry place, in tightly sealed containers at 2-25°C.

MilliChrome is a trademark of Merck KGaA, Darmstadt, Germany