● Prepare media made from dehydrated products in as damp-free an environment as possible. To prevent the risk of inhaling fine particles of dehydrated media, wear a dust mask while handling dehydrated media.
● Wash the hands immediately after preparing media.
● Once the ingredients are weighed, do not delay in making up the medium. Follow exactly the manufacturer’s instructions.
● Use completely clean glassware, plastic or stainless steel equipment that has been rinsed in pure water. The container in which the medium is prepared should have a capacity of at least twice the volume of the medium being prepared.
● Use distilled water from a glass still. Deionized water can also be used providing the exchange resins do not contain substances inhibitory to bacteria (preparation of deionized and distilled water in district laboratories is described in Water containing chlorine, lead, copper, or detergents must not be used. Besides containing substances harmful to bacteria, impure water can alter the pH of a medium or cause a precipitate to form.
● Add the powdered or granular ingredients to the water and stir to dissolve. Do not shake a medium but mix by stirring or by rotating the container.
● When heating is required to dissolve the
medium, stir while heating and control the heat to prevent boiling and foaming which can be dangerous and damage the medium, e.g. DCA or TCBS agar. Overheating a medium can alter its nutritional and gelling properties, and also its pH.
● Autoclave a medium only when the ingredients are completely dissolved. Always autoclave at the correct temperature and for the time specified
● Dispense medium in bottles or tubes in amounts convenient for use. Know the length of time prepared media can be stored without deteriorating (take into account storage temperature)
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