As expressly stated in Art. 53(b), second half-sentence, the exception referred to in the first half-sentence does not apply to microbiological processes or the products thereof.[Art. 53(b); Rule 26(6); ]

"Microbiological process" means any process involving or performed upon or resulting in microbiological material. Hence, the term "microbiological process" is to be interpreted as covering not only processes performed upon microbiological material or resulting in such, e.g. by genetic engineering, but also processes which as claimed include both microbiological and non-microbiological steps.

The product of a microbiological process may also be patentable per se (product claim). Propagation of the microorganism itself is to be construed as a microbiological process for the purposes of Art. 53(b). Consequently, the microorganism can be protected per se as it is a product obtained by a microbiological process (see G‑II, 3.1). The term "microorganism" includes bacteria and other generally unicellular organisms with dimensions beneath the limits of vision which can be propagated and manipulated in a laboratory (see T 356/93), including plasmids and viruses and unicellular fungi (including yeasts), algae, protozoa and, moreover, human, animal and plant cells. Isolated plant or animal cells or in vitro plant or animal cell cultures are treated as microorganisms, since cells are comparable to unicellular organisms (G 1/98, 5.2).[Rule 27(c); ]

On the other hand, product claims for plant or animal varieties cannot be allowed even if the variety is produced by means of a microbiological process (Rule 27(c)). The exception to patentability in Art. 53(b), first half-sentence, applies to plant varieties irrespective of the way in which they are produced.