The Shelf-life of Microbiological Media
Did you know that the composition and packaging of the medium determine its susceptibility to deterioration during storage.
For example, the presence of blood, antibiotic or heat sensitive inhibitors will severely limits the useful life of a medium. The optimum storage temperature for the majority of prepared media is between 4°C to 6°C. When temperatures exceed these ranges, the shelf-life of the medium decreases
Most liquid media do not deteriorate at 4°C for many months but some have a tendency to form deposits, especially those of double strength. Some liquid media have short shelf life even at 4°C, for example, tetrathionate broth.
A volume check should be made on older stock that may be susceptible to evaporation.
It is important to prevent exposure of culture media to sunlight, as this may adversely affect their performance through the formation of peroxides, or by affecting the stability of dyes. Most solid media keep for many months if stored in an airtight container, however there are notable exceptions (e.g. some formulations of Baird-Parker medium).
Agar gel is normally very stable but in media with a pH of less than 5 softening may take place during sterilization, subsequent storage, or re-melting. Therefore storage of agar plates presents two main problems: 1. Contamination and 2. Dehydration.
The length of time that plates can be kept before use depends on the ability to prevent contamination and to minimise loss of moisture. Both of these effects may be reduced by wrapping and sealing plates in plastic bags or cellophane during storage at 4°C, and by implementing effective stock rotation programs within the laboratory.
http://biology.clc.uc.edu/fankhauser/Labs/Microbiology/Media_Prep/010_recap_securely_P7120130.JPG
