Bacteria are single-cell organisms that can cause various diseases in plants.
Bacteria are often spread through the starting material. A latent infection may be present in this starting material (seed potatoes). During the cultivation and processing of the seed potatoes, the bacteria can easily spread and be transmitted, for example, by water, machines or boxes. That is how a minor latent infection can slowly grow and develop.
The two most important measures for preventing bacterial diseases are early detection and strict hygiene measures.
The most important and common bacteria belong to the Pectobacterium. In potatoes, there are roughly four types that can cause problems. The Pectobacterium atrosepticum, parmentieri and brasiliensis (PCA, PAR and PCB) which cause blackleg and wet rot and the dickeya (DIC) which causes stem wet rot.
There are also the quarantine diseases ring rot (clavibacter) and brown rot (ralstonia).
You will find more information on quarantine diseases here (External link, Dutch only).