A substance or reactant intended to be used together with a parent IVD to perform a specific function in an assay that is used to determine the degree of susceptibility or the minimum inhibitory concentration (MIC) of a range of antibacterial/antibiotic agents (i.e., a drug intended for treatment and/or prevention of a bacterial infection, excluding mycobacterial infection) against a specific bacterial microorganism, isolated from a clinical specimen by culture.