Description
Levine EMB Agar is a high-performance selective medium specifically formulated for the isolation and differentiation of coliform bacteria, particularly Escherichia coli (E. coli). This essential laboratory medium is widely used in microbiological testing for food and water safety, ensuring the identification of lactose fermenters while inhibiting gram-positive bacteria.
Composition and Preparation
The approximate formula includes key ingredients such as Pancreatic Digest of Gelatin (10.0 g/l), Lactose (10.0 g/l), Dipotassium Hydrogen Phosphate (2.0 g/l), Agar (15.0 g/l), Eosin Y (0.40 g/l), and Methylene Blue (0.065 g/l), achieving a final pH of 7.1±0.2 at 25°C. To prepare, simply suspend 37.4 g of Levine EMB Agar in one liter of distilled or deionized water, heat with agitation, and sterilize in an autoclave at 121°C for 15 minutes.
Principles and Interpretation
Eosin Y and methylene blue are vital in rendering this medium slightly selective, effectively inhibiting certain gram-positive bacteria. These dyes not only act as indicators but also facilitate the differentiation between lactose fermenters and non-fermenters. In an acidic environment, these dyes form a complex that serves as an inhibiting agent, while the pancreatic digest of gelatin provides essential nutrients and growth factors. The phosphates included function as an effective buffering agent, making this medium ideal for E. coli, which produces colonies characterized by a distinctive green metallic sheen, indicative of robust lactose fermentation.
Appearance and Quality Control
The dehydrated form of Levine EMB Agar is a free-flowing purplish-red powder, and the prepared medium appears as a purplish-red brown gel. For quality assurance, it’s recommended to inoculate and incubate at 30-35°C for 24-48 hours to verify performance.
Storage and Shelf Life
To maintain optimal performance, Levine EMB Agar should be stored tightly capped in its original container at 5-30°C. The dehydrated medium boasts a shelf life of 3 years from the date of manufacture, while prepared medium should be stored out of direct light at 2-8°C.
Precautions
This medium is for laboratory use only. Avoid using dried medium that is past its shelf life, has caked, or shows color variation.
Levine EMB Agar is essential for microbiologists conducting thorough analyses in food safety and water quality testing. With its selective properties and reliable performance, it stands out as the go-to medium for effective coliform isolation and differentiation, ensuring compliance with industry standards.
Microorganism | Strains
Number |
Inoculum
(CFU) |
Growth | Recovery | Remarks |
Escherichia coli | ATCC 25922 | 10-100 | luxuriant | ≥50% | Green metallic sheen,
blue-black colonies |
Staphylococcus Aureus | ATCC 6538 | 100-1000 | inhibited | <1% | / |
Escherichia coli | ATCC 8739 | 10-100 | luxuriant | ≥50% | Green metallic sheen,
blue-black colonies |
Salmonella typhimurium | ATCC 14028 | 10-100 | luxuriant | ≥50% | Colorless colonies |
Reviews
There are no reviews yet.