Saturday, 29 August 2020

Modern myth #5: Freeze-dried cultures are safe until they are reconstituted

The number of particles aerosolized upon opening lyophilized cultures depends upon the consistency of the end product. For example, fluffier end products tend to create more concentrated aerosols. Most of the particles aerosolized upon opening lyophilized cultures are larger than 5 um. Dropping a lyophilized culture creates an extremely concentrated aerosol composed predominantly of particles larger than 5 um.

The inclusion of mother liquor in the suspending menstruum reduces the aerosol concentration approximately fourfold.

Two parameters must be established to assess the risk of handling laboratory cultures: the biological decay rate of aerosols under laboratory conditions, and the human infectious dose by the respiratory route. Several common organisms survive at least 1 hour in droplet nuclei at standard laboratory relative humidity.


Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (

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