Bactericidal Substances

substances capable of killing bacteria and other microorganisms. In the latter case, bactericides are distinguished as fungicides, which act on fungi; amoebicides, which kill amoebas; and so on. Bactericidal substances include compounds of varying chemical nature: phenol, mercury chloride, alcohol, formalin, hydrogen peroxide, antibiotics, and such gases as sulfur dioxide, ethylene oxide, and methyl bromide. The immune antibodies produced in the blood of animals and man are also bactericidal. Bactericidal substances quickly kill the vegetative cells of bacteria; bacterial spores are more difficult to destroy. The mechanism of action of bactericidal substances varies— some denature microbial protein, others attack certain enzyme systems, and so on. Since not all the microorganisms of a population are equally sensitive to these substances, the use of submaximal concentrations enables some of the microbes to survive (partial bactericidal capacity) and give rise to races resistant to bactericidal substances. Therefore the bactericidal substances must be administered in rather large doses when used in the treatment of disease. Their activity decreases in the presence of proteins (pus, serum, milk, and others). Bactericidal substances are used for purposes of sterilization—that is, as disinfectants or antiseptics—and for chemotherapy.