Bacteriostatic Substances

antibiotics, metallic ions (Ag⁺, Au³⁺, Hg²⁺, Cu²⁺), chemotherapeutic drugs (sulfanilamides, arsenicals), and other substances that completely inhibit propagation of bacteria or other microorganisms, that is, which cause bacteriostasis. The action of bacteriostatic substances is reversible: when they are removed or when deactivators of bacteriostatic substances are added, bacterial growth is resumed. For example, the action of metallic ions ceases in the presence of hydrogen sulfide, which rids the bacterial cell surface of the ions. The effects of bacteriostatic substances are also curtailed by substances with high adsorptive capacity (for example, proteins). This explains the decrease in activity of bacteriostatic substances in the presence of blood, pus, and so on. In small concentrations, bactericidal substances also have a bacteriostatic effect. Bacteriostatic substances act as medications by suppressing the reproduction of pathogenic microbes in the bodies of man and animals. By means of bacteriostatic substances harmless to man, various food products—wine must, milk, and others—are protected from microbial spoilage. For this purpose, benzoic acid or exposure to sulfur dioxide gas, hydrogen peroxide, and various antibiotics not used in medical practice are used.