Desiccation ( loss or lack of water) results in loss of metabolic activity, followed by decrease in the total viable population. The time of survival of micro organisms after dssication varies depending upon –the type of the micro organisms, materialin or on which the micro organisms are dried, the completeness of the drying process, the physical conditions in which the dried organisms are exposed eg. light, temperature and humidity
Many vegetative cells are killed in a matter of few hours by drying for eg. gonococci and meningococci . some organisms like streptococci are more resistant and can survive for weeks after drying. While pathogens like mycobacterium tuberculosis can survive for even longer periods. Spores may be dried and kept for years under the laboratory conditions. Thus dessication is not an aggnt for sterlisation, like low temperature is considered as microbiostatic.
Lyophilisation is the process of subjecting the micro organisms to extreme dehydration in frozen state and then sealing under vacuum. Lyophilised cultures of the micro organisms remain viable for years