Part of Thermo Fisher Scientific

Thermo Scentific
 
 
 

Dehydrated Culture Media

LYSINE MEDIUM

Code: CM0191

A synthetic medium for the isolation and enumeration of wild yeasts encountered in brewing. On this medium, pitching yeasts are suppressed.

Typical Formula*

gm/litre

Glucose

44.5

Potassium dihydrogen phosphate

1.78

Magnesium sulphate

0.89

Calcium chloride fused

0.178

Sodium chloride

0.089

Adenine

0.00178

DL-methionine

0.000891

L-histidine

0.000891

DL-tryptophane

0.000891

Boric acid

0.0000089

Zinc sulphate

0.0000356

Ammonium molybdate

0.0000178

Manganese sulphate

0.0000356

Ferrous sulphate

0.0002225

Lysine

1.0

Inositol

0.02

Calcium pantothenate

0.002

Aneurine

0.0004

Pyridoxine

0.0004

p-aminobenzoic acid

0.0002

Nicotinic acid

0.0004

Riboflavin

0.0002

Biotin

0.000002

Folic acid

0.000001

Agar

17.8

pH (see directions)

* Adjusted as required to meet performance standards

Directions
Suspend 6.6g in 100ml distilled water containing 1.0ml Potassium lactate SR0037. Bring to the boil to dissolve completely. Agitate frequently to prevent superheating. Cool to 50°C and add 0.1ml of lactic acid 10% SR0021 to adjust to pH 4.8 ± 0.2. Dispense into Petri dishes and remove surface moisture by drying at 37°C.

Description
A complex medium, originally described by Morris & Eddy1 for the isolation and enumeration of wild yeasts in pitching yeast. Walters and Thiselton2 examined 180 species of yeasts in a liquid synthetic medium containing lysine as the sole nitrogen source. They found that no normal cerevisiae or carlsbergensis strains utilised lysine whereas many other yeasts, including wild yeasts, did so. They kept their stock cultures on malt extract agar slopes or on malt extract chalk agar in the case of Brettanomyces species. Later, Morris & Eddy1 described a solid lysine medium for the isolation and enumeration of wild yeasts in pitching yeast. Oxoid Lysine Agar is made to their published formula.

Technique
Wash and centrifuge the sample of pitching yeast three times with distilled water. Remove 0.2ml of a suspension containing approximately 107 cells per ml and spread with a bent platinum wire, over the surface of a Lysine Medium plate. Incubate at 25°C and examine daily for evidence of growth. Count the number of colonies which develop, and express the degree of contamination as the number of wild yeast cells per million cells of the original inoculum.

The number of cells in the inoculum is important as it has been shown by Morris & Eddy that small numbers of cells (approximately 100 to 1,000) still grow to a limited extent on the medium. Where the number of brewing yeast cells exceeds approximately 10,000, a count of the colonies developing provides a direct measure of the contamination by wild yeasts3.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium at 2-8°C.

Appearance
Dehydrated medium: White coloured, free-flowing powder
Prepared medium: Light straw coloured gel

Positive control:

Expected results

Pichia fermentans ATCC® 10651

Good growth; white colonies

Negative control:

 
Saccharomyces (carlsbergensis) uvarum ATCC® 2700Slight background film

Precautions
The pitching yeast may grow as a slight background film with the `wild’ yeast appearing as colonies on the film.

References
1. Morris E. O. and Eddy A. A. (1957) J. Inst. Brew. 63(1) 34-35.
2. Walters L. S. and Thiselton M. R. (1953) J. Inst. Brew. 59. 401.
3. Fowell R. R. (1965) J. Appl. Bact. 28. 373-383.

 
©2001 - 2021 Oxoid Limited, All rights reserved.
Copyright, Disclaimer and Privacy Policy | Conditions of Sale | About Us | Cookies
Thermo Fisher Scientific Inc.