For pre-painted surfaces, contamination comes essentially from the air and it is important to have a relevant test to characterize the surface behaviour towards bacteria according to its conditions of use. A colour test is introduced that enables to detect active or dead bacteria directly on a contaminated surface. Means to avoid the proliferation of microorganisms are presented. The behaviour of two pre-painted topcoats doped with organic and inorganic bactericidal additives is described. On fresh and clean surfaces, the organic coatings have a very slight biocide effect. The weakest bacteria are rapidly destroyed whereas the more resistant ones are only inactivated several days later. On fouled surfaces, the bacterial destruction is very limited. In the selected experimental conditions, the standard pre-painted topcoat has the same behaviour as the doped ones.