Listeria Chromogenic Medium

Description: used for rapid detection of Listeria monocytogenes in food and medicine. Negative results can be detected completely in three days. The colonies of Listeria monocytogenes is blue, surrounded by an opaque ring. On recipe, peptone provides nitrogen and amino acids, sodium chloride maintains osmotic pressure, agar is coagulants, lithium chloride inhibits the growth of Gram-negative bacteria, bacteriostatic agents inhibits the growth of Gram-positive bacteria, except Listeria.

Ingredients (g / L)

Additives:

Listeria additive 6.0g

Listeria bacteriostatic agent 1 1mL* 5 pieces

Listeria bacteriostatic agent 2 1mL * 5 pieces

*Adjusted and/or supplemented as required to meet performance criteria.

Directions:

Suspend 14.2g /180ml, and weigh 1.2g Listeria additive, add 20ml of sterile water and some glass balls, , both are autoclaved at 121 ℃ for 15 min. When cooling down to about 50 ℃, put the Listeria additive into the base medium, and add each one piece of Listeria antibacterial agents 1 and 2, mix evenly, pour into sterile petri dishes. Medium thickness is about 5mm, so advantageous to observe opaque ring.

Procedures:

Before to use, the prepared medium is placed at room temperature for 10-20 minutes

1. Prepared sample solution according to national standards, SN standard, FDA standards or other methods.

2. Put samples solution into Listeria enrichment broth (LB1, LB2) for enrichment culture; or the sample solution and the Half-Fraser enrichment broth according to the mixing ratio of 1:10, 30 ℃ for 24 hours; Or other enrichment broth for enrichment culture;

3. Take one ring enrichment broth, streak and inoculate on Listeria chromogenic medium, culture for 24-48 hours at 37 ℃.

Quality Control:

1. Appearance:

The dehydrate powder medium is homogeneous, having good flowability; yellowish, prepared medium is opaque milky white solid.

2. Microbial sensitivity test:

Incubated at 37 ℃ for 24-48 hours:

Typical features:

Listeria monocytogenes culture for 24-28 hours at 37 ℃, each of blue colonies are surround by an opaque ring. Listeria iuanuii culture for 48 hours at 37 ℃, each of blue colonies are surrounded by an opaque ring. Listeria seeligeri culture for 24-48 hours at 37 ℃, blue colonies appear, no opaque ring around. Listeria iuanuii inspection is very rare in food.

Storage:

The prepared plates can be kept for 2-8 ℃ avoid direct exposure to light. The powder medium should be placed in a dark, dry place, storage temperature 2-8 ℃, avoid direct exposure to light.

Failure:

Dry powder media which are over the shelf life, caking and color variation cannot be used.

Note:

This medium is only for laboratory use.

Reference:

1. VAN NETTEN, P., PERALES, J., VAN DE MOOSDIJK, A., CURTIS, G.D.W., a. MOSSEL, D.A.A.: Liquid and solid selective differential media for the detection and enumeration of Listeria monocytogenes.  Int. Food Microbiol., 8; 299-316 (1989).

2. HAMMER, G., HAHN, G., KIRCHHOFF, H., a. HEESCHEN, W.: Vergleich der Eignung von Oxford- und PALCAM-Medium zur Isolierung von Listeria monocytogenes aus Weichkäse.  Dtsch. Milchwirtschaft,41; 334-336 (1990).