Described is an object surface coating comprising one or more polymers and a peptide covalently linked to at least one of said one or more polymers, said peptide comprising a) a first cleavage site, wherein said first cleavage site is cleaved by a first compound specifically provided by a microbe belonging to a first group consisting of a limited number of microbial strains, species or genera, and not cleaved by any compound provided by any microbe not belonging to said first group, b) a first fluorescent agent having an emission wavelength of 650-900 nm, c) a first non-fluorescent agent having an absorption wavelength of 650-900 nm, for quenching said emission of said first fluorescent agent, wherein cleavage of said first cleavage site results in the release of said first non-fluorescent agent from the coating, the release of said first non-fluorescent agent being indicative for the presence of a microbe belonging to said first group.