The Atomic Force Microscope (AFM) is used as a detector of viability of cells and bacteria. The biological specimens are attached to the cantilever of the Atomic Force Microscope and the fluctuations in the deflection of the cantilever are monitoring the viability of the bioorganisms. We show how it is possible to detect resistance or susceptibility to antibiotics of bacteria with this method. This new method might be employed to decisevely speed up the diagnostics of antibiotics resistance of bacteria. Mammalian cells can also be adsorbd unto the cantilever of the AFM and the effect of drugs or potentially harmful proteins can be monitored in this way: examples of this type of experiments concern the effect of anticancer drugs and the effect of amyloidal proteins aggregates. We relate the measured effect on the fluctuations in the cantilever's deflection to the mechanical motion of the biological organism that are related to the metabolism of the same.