Isolation and Characterization of Leuconostoc Meseteroides from Cheese – Part 1

Leuconostoc:

This genus was called as Betacoccus by Oria – Jensen. It contains the heterofermentative lactic bacteria, which ferments sugars to produce 50% lactic acid, plus, 25% acetic acid and ethyl alcohol and 25% carbon dioxide. These other compounds are important as they impart particular tastes and aromas to the final product. The major subsps of Leuconostoc are,

Leuconostoc mesenteroides
Leuconostoc dextranicum
Leuconostoc cremoris
Leuconostoc lactis

Sources Of Leuconostic:

Leuconostoc are used as mesophilic starters in combination with other starters for making cottage and cream cheese, cultured milk, buttermilk. It produces acetic acid from citrated and may be added to cottage cheese to prevent spoilage by slime producing Pseudomonades. Leuconostoc are also found in milk and milk products, vegetables, plant surfaces. Dextrans produced by Leuconostoc mesenteroides are used as stabilizers in ice cream mixes.

Special Focus On Leuconostoc MesenteroidesS:

Leuconostoc mesenteroides differs from other lactic acid species as it can tolerate fairly high concentration of salt and sugars (unto 50% sugar). Leuconostoc mesenteroides initiate growth in vegetables more rapidly over a range of temperatures and salt concentration than any other lactic acid bacteria. It produces carbon dioxide and acids which rapidly lower the pH and inhibit the development of undesirable microorganisms. The carbon dioxide produced replaces the oxygen, making the environment anaerobic and suitable for the growth of subsequent species of lactobacillus and inhibits the growth of aerobic micro flora. Removal of oxygen also helps to preserve the color of vegetables and stabilizes any ascorbic acid that is present.

These characters of Leuconostoc mesenteroides made me to focus on its isolation and characterization, further more antimicrobial activity, bacteriocin.

Growth Requirements

Leuconostoc have a complex growth requirement with an optimum temperature of 20-30°C. They are fastidious chemo organotrophic bacteria requiring rich nutrient sources such as carbohydrates, nitrogen sources, salts, vitamins and sugars. The medium used for the isolation and enumeration of Leuconostoc was MRS medium (Man Rogosa Sharpe Medium). MRS medium contains all the essential substrates for the growth of Leuconostoc.

In isolating Leuconostoc from nature or food samples, the combination of the presence of agents inhibitory to most lactic acid bacteria other than Leuconostoc spp and the agents stimulatory for Leuconostoc spp in the medium selects for Leuconostoc spp.

The vancomycin resistant character of Leuconostoc spp. favored for the isolation from cheese sample. Other lactic acid bacteria are vancomycin sensitive. MRS medium containing 30mg/ml concentration of vancomycin was used as the special medium for Leuconostoc isolation. Comprehensive reviews of Leuconostoc differential and selective medium have been published by Garvie, Tenber & Gets and Cogan.