A biological indicator for monitoring the effectiveness of a sterilizing, disinfecting treatment or process. A compound or condition is disclosed which comprises a substrate having a surface layer containing functional groups thereon desirably free of silicon linking groups. The functional groups are desirably in the form of a monolayer of a uniformed distribution and of a selected quantity. Various types of microorganism indicators, such as spores and/or etiological agent indicators are covalently bonded to the surface layer functional groups through a crosslinking reagent and thus form a uniform number and distribution of the microorganism and/or etiological agent indicators. After being subjected to sterilization or other similar disinfecting treatments or processes, along with various articles such as instruments, the indicator can be cultivated to determine the effectiveness of the sterilization, disinfection, etc. treatment or process.