"I need inert and non-water absorbent adhesive film, with good sealing properties, to cover a surface (ceramic) already covered with a suspension of bacteria (dried). This set will be placed in a stomacher bag that contains culture media and the bacteria should be able to pass from the adhesive film to the media. It must be sterile or be able to be sterilized."
There are a few different options, depending on whether you want it to be sticky or non-sticky, or somewhere in between. Various silicone manufacturers or converters may offer cured silicone sheet in various durometers that would be inert and non-water absorbant. The lower the durometer (A-5 to A30), the better it will seal, but will be soft and “grabby” to the touch. Higher durometer silicone will be slightly easier to handle, but will not be as sticky or grabby as the lower durometer materials. You can go with an even lower durometer with silicone gels for better adhesion, but these need to be on a backing (similar to the tacky gel woundcare dressings or ouchless bandaids). Thin film PTFE or PTFE tape may also be an option. Many of these options will be sterilizable.