Culturing and Preparing Bacteria
Using good aseptic culturing technique, grow cells in liquid culture or on agar plates until solid cultures are dense or liquid cultures are in early stationary phase. In practice, this would be equivalent of shaking a bacterial culture overnight or letting cells grow on a plate for 1-2 days. For agar cultures, growing cells on slants (glass tubes) may be more practical as it omits the centrifugation step below. However, liquid cultures normally yield a greater number of viable cells.
For liquid cultures, the cells are centrifuged, the culture broth is removed, and the pellet is suspended in an equal volume of lyophilization medium. We recommend Reagent 18 or the Microbial Freeze Drying Buffer, though skim milk and sucrose will work. For agar cultures, flood the plate/tube with 5-10 ml of lyophilization medium. Using a sterile pipette, flush the medium over the colonies to dislodge the cells. Transfer the cell suspension to a sterile tube. We recommend that a cell count is performed which can be compared to cells following freeze drying. A simple dilution to extinction protocol is available here.
Aliquot the cell suspension into sterile vials or tubes. Only 250-500 μl is needed per vial as this represents around 108 bacteria. Place split stoppers on the vials or loosely plug tubes with glass wool. Vials with split stoppers are technically open to the air, thus at risk of contamination. In practice we have not found this to be an issue. If a vial contains upwards of a billion bacteria, one or two contaminating microbes become insignificant when that culture is rehydrated and streaked. If there is fear of contamination, or containment, then glass wool or cotton can be placed under the stopper to prevent contamination.
Freeze Drying Process - Shelf Lyophilizer