Why are using Seed lot Techniques for microbial culture?

• Seed lot Technique is recommended for storage of the microbial culture for long time.
• As per USP general chapter 51 ( Antimicrobial effectiveness Testing) and 1117 (Microbiological best laboratory practices) seed lot techniques is better for maintain the reference cultures (master seed) in the laboratory.
• Seed lot technique used to avoid the microbial contamination  and cross contamination.
• To reduce the possibility of phenotypic variation, genetic drifts, mutations and contamination as much as possibles the number of passages  should be minimized ( five passages).
• Seed lot technique to prevent  the unwanted drift of properties which might ensure from repeated subcultures or multiple generation.
• Seed lot technique reference strain is sub cultured to several replicates at one time, all of which are with one passage( seed stock is sub cultured).
  
• Stock cultures can be sub cultured for reference cultures and working cultures, Reference cultures monthly basis  and working cultures weekly basis.
• Frozen cultures should be stored at -30 degree C or below, until use. If stored at -70 degree C or below in lyophilized form. Slants may be stored at 2 to 8 degree C for up to a week.
  

Related : What is the meaning of passage? how many passages are acceptable in the laboratory?