The spread of drug-resistant bacteria represents a growing worldwide health problem. The most efficient way to fight drug-resistant bacteria is to detect their colonies, identify their type, monitor their growth, and destroy them before they reach the human body. A gravimetric biomedical micro-electro-mechanical sensor (BioMEMS) system operating in the pico-gram range (10(-)(12) g/cm(2)) has been proposed for detecting growth of drug-resistant bacterial colonies. The sensor is based on a MEMS metal-coated thin piezoelectric membrane resonator. A combination of shear horizontal surface acoustic (SHSAW), Bleustein-Gulyaev, skimming and 'leaky' waves, generated in the resonator, are highly sensitive to mass, density, viscoelastic, and electrochemical changes at the resonator/bacteria interface. Measuring resonant frequency shifts of the composite resonator provides information about the mass and type of the bacterium colony growing on the resonator.