Biology Question #329

Krisy Marsh, a 20 year old female from the Internet asks on February 2, 1998,

How would one maintain a bacterial culture without having to transfer cultures on a regular basis?

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The answer

Wendy Hutchins answered on October 5, 2004

I concur that ATCC is invaluable on storage and growth of bacteria. Check out their FAQ page. There is a more recent study on lyophilization of Chlamydia in the Journal of Applied Bacteriology, 1993 Nov;75(5):473-7. This will be available in large public libraries or university libraries. If chlamydia can survive, anything can and lyophilization is next to -70 degrees C storage as one of the most permanent storage solutions. Lyophilized strains can be stored at room temperature as well, but losses do increase over time in both storage methods and it depends on the bacteria genus and species. One additional method for storage of common lab strains (non-fastidious) and anaerobes is to grow them in a cooked meat medium and then store them at room temp (cool and dark). E.coli and others can live a year in such a medium. Fastidious bacteria, such as Streptococci are best frozen at -70 as described in glycerol or lyophilized.

Philip McIntosh answered on February 2, 1998

There are several ways to do this.

  1. Lyophilization (freeze drying). The cells are immersed in liquid nitrogen and then dried under a vacuum. Sounds harsh doesn't it?

    However, many microorganisms can "come back to life" after this treatment when rehydrated. The lyophilized cells must be stored at a very low temperature (as in a liquid nitrogen Dewar).

  2. Refrigeration. You can keep bacteria alive on regular laboratory medium (in tubes or Petri dishes) for an extended time just in a refrigerator at about 4°C.

    This way, strains need be only transferred every few months or so.

  3. Super-cooling. You can mix them up in a glycerol solution and keep them at -70°C for long periods of time (years).

Not all organisms store equally well using these techniques and some modifications are frequently necessary to insure viability. Consult the American Type Culture Collection manual for details on how they store particular strains for extended periods.

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