The adverse effect of a substance or activity on microbes or cells is called its mode or method of action. We do not understand exactly how many controls destroy microbes, but we do recognize that the exact method of action may be very complex.

Some controls change the environment around the microbe and reduce the potential growth of the microbes. Dehydration, removal of oxygen, changing pH, and addition of salt, smoke, sugar or other chemicals may inhibit the growth of many microbes. We dehydrate or vacuum pack foods to reduce microbe growth. The early Egyptians amazed us by embalming bodies of the dead with salts and oils. Dairy workers and scientists have realized that dry bedding inhibits the growth of E.coli and reduces the incidence of environmentally induced mastitis (udder infections). Agronomists and crop farmers are aware that the humidity and moisture on the wheat flowers are sometimes directly related to the later incidence of wheat scab or Fusarium infections. Many health science employees like nurses, respiratory care practitioners, and others know that covering or packaging equipment keeps the equipment dry and less likely to support the growth of microbes.

Other controls alter the microbe cell envelope by changing the capsule, cell wall, cell membrane, or surface motility structures. No movement by a microbe does not always mean a dead microbe. The cell wall of microbes is essential for the life of most bacterial and fungal cells. Controls that block the making of the cell wall or break down the cell wall deprive the cell of its rigidity and shape. The enzymes in tears (lysozyme), antibiotics like penicillin, and some detergents and alcohols may weaken the cell wall. The selectively permeable cell membrane of all microbes (even some viruses) is essential for the survival of the microbe. Microbial death usually follows the development of holes in the cell membrane. Ethyl alcohol, certain detergents and antibiotics like polymyxin damage cell membranes.

Still additional controls damage the inner cytoplasm, proteins, ribosomes, mitochondria, or nucleus of the cell. Controls that denature (destroy) cell proteins are the most effective destroyers of microbes. A control that alters the proper synthesis of proteins or changes the genetic code of a cell prevents the growth, metabolism, and reproduction of the microbe. The irreversible denaturing (changing) of proteins resulting from breaking of protein bonds results in the death of microbe cells; such controls include moist heat, heavy metals, and strong organic solvents like phenols.