Microorganisms are specialist types of plant protection and public health substances that require certain specialist know-how. They are microorganisms (protozoan, fungus, bacterium, virus, or other microscopic self-replicating biotic entity) and any associated metabolites, to which the effects of pest control are attributed.

A MPCA and MPCP may contain:

• Viable and/or non-viable microorganisms.
• Secondary compounds (also may be called secondary metabolites) produced during cell proliferation (growth) and they may or may not be toxicologically relevant.
• Material from the growth medium.

Any, or all, of these components can contribute to activity against the target.

Therefore:

• Registration is not just species but strain specific and so correct taxonomy of the species and strain is vital.
• Production method is specific to the composition of each MPCA. Microorganisms are produced in vivo or in vitro by specific fermentation processes, the type of production method and the downstream processing method will alter the type of active substance and determine whether it contains cells, spent fermentation media and/or secondary compounds (metabolites).

When is bridging possible

The only circumstances when it is reasonable to consider bridging from one MPCA to another one are when the following criteria are fulfilled:

• The strains are identical.
  This can be confirmed for example by a complete paper trail to the acquisition of the microbial culture that was originally stored in the international tissue collection, genetic methods confirming it to be identical provided it uses the same method as was used to identify the original strain.
• The production methods are identical.
  For in vivo production, the host organism is the same species. For in vitro production, the fermentation process is identical (for the inoculum, the fermentation media, the production methods and conditions, the harvesting, the downstream processing, the storage of the MPCA).

The criteria to allow bridging for any of the data requirements (human, residues, environmental, non-target safety) are the same as for Technical Equivalence.