Development of Protocol for Dry Heat Inactivation of Escherichia Coli DH5α

Abstract

Dry heat removal of water is a common method for industrial drying to preserve food. But, in biotechnology research applications, freeze drying is a more common method to prepare cells for various analytical instrumentation analysis such as scanning electron microscopy or atomic force microscopy. This work attempts to validate a dry heat inactivation protocol for Escherichia coli cells cultivated in LB Lennox medium and harvested by conventional centrifugation process. Results revealed a two phase drying phenomenon at 60 oC in an oven. First phase of drying was more rapid than the second phase, where it likely involves the removal of surface water from the cell pellet. In the second phase, pore water from channels in the cell pellet lined by aggregates of E. coli cells are removed by dry heat at a slower rate. Overall, 18.5 hours was needed to remove most of the accessible water to produce a good constancy dry cell pellet with some water of hydration remaining in individual cells.

Keywords: dry heat, Escherichia coli, pore water, surface water, water of hydration