There are a number of ways that we control pathogens and there are numerous antimicrobics that we use to treat infectious diseases. In some cases we only seek to prevent the growth of potential pathogens—in other cases we seek to kill or inactivate the potential disease causing microbes. There are a number of physical and chemical ways of controlling potential pathogens. Heat is one way that we reduce the numbers of potential pathogens. Ifwe can heat a liquid to 121C and hold it there for 15 minutes all bacteria (including those that form endospores) should be killed and allviruses inactivated. To achieve this temperature we normally use an autoclave which uses steam at 15 lbs per square inch pressure to achieve the temperature of 121C. Most of the media used to culture bacteria in the laboratory are sterilized using an autoclave. For home canning a pressure cooker is used for this same sterilization process. Sterility means that there are no living organisms—the presence of even a single live bacterium would mean that the substance was not sterile. In some cases we do not seek to kill all microorganisms but simply to eliminate the non-spore formers and potential pathogens. In some cases we simply boil water (100C) for a few minutes to ensure that there are no enteric pathogens that may have entered through fecal contamination. Milk will not withstand the high temperatures (100-121C) for prolonged periods like 15 minutes. For milk rather than trying to eliminate all viable microorganisms we generally aim at just reducing the numbers so that it has an extended shelf life (does not spoil quicklydue to microbial growth) and so that a number of pathogens are eliminated. In particular we try to make sure that Mycobacterium and Salmonella are eliminated. To do this we either use a temperature like 72C for a few minutes or 63C for a longer period of time. This process is called pasteurization. Again it is aimed at lowering the numbers of total bacteria and eliminating non-spore forming pathogens. Pasteurization though does not kill spore formers like Clostridium. Because pasteurization does not result in sterility the milk needs to be refrigerated to prevent spoilage. It is possible to sterilize milk by using a very high temperature (200+C)for just under 2 seconds. This process results in sterilization. Milk produced this way is labeled UHT (ultra high temperature) and has an indefinite shelf like and does not need to be refrigerated because it issterile. In some cases heat cannot be used as it would destroy the material. One can remove bacteria from liquids by filtration. Filtration is a physical process that relies upon a filter with very small pores (0.2-0.45microns) For some medical fluids filtration is used to achieve sterility. Water can also be sterilized by filtration. For solid materials like plastics heat would destroy the material. In such cases it is possible to use radiation (gamma rays) to kill the bacteria. The plastic petri dishes and pipettes that we use in the laboratory are sterilized by exposure to radiation. Some foods now are also sterilized in this manner to extend their shelf lives. The radiation source never directly contacts the food or plastics. No radiation is retained. But the bacteria and other microorganisms are killed. In other cases gaseous chemicals are used to achieve sterility. Beds and bedding from an infectious disease ward can be sterilized by exposure to ethylene oxide. This gas is toxic to microorganisms. It is also toxic to humans. The item to be sterilized, which can be a hospitalbed, is placed into a sealed chamber and the ethylene oxide is then introduced. After a suitable exposure time the ethylene oxide is slowly vented in the atmosphere at levels deemed to be safe. The chamber can then be opened and the bed or other material safely removed. Many hospitals have ethylene oxide sterilizers. In the case of the anthrax attacks of 2001 chlorine dioxide was used to kill any anthrax spores that might have remained in postal offices. Thebuilding were sealed and chlorine dioxide was introduced. The building have since been safely reopened. Other chemicals with chlorine are used to kill potential pathogens. Chlorine is used to kill bacteria in water and swimming pools. Bleach (hypchlorite) is used to kill bacteria on many counter tops. Glutaraldehyde can be used to sterilize medical instruments—this chemical kills spores as well as vegetative cells. Heavy metals also can be used to kill bacteria. If you place a copper penny on the surface of agar inoculated with bacteria in a petri dish you would observe no bacteria growing near the penny. This killing of microorganisms by heavy metals is called the oligodynamic action. IF you were to pass through the Atlanta airport you would see signs next to the drinking water fountains saying that copper had been used to render the water safe to drink. In some dental offices silver is used to prevent the growth of bacteria, like Legionella, in the water lines.Various other halides are also used to kill bacteria. Bromine is used for home spas. Such agents are broadly called disinfectants. Sometimes they are also referred to as germicides because the aim to kill pathogens. Watch the TV ads for Lysol and you will see claims that is auseful disinfectant/germicide. There also are a number of substances other that can be used as disinfectants on inanimate surfaces but are not considered safe for skin application of to be taken internally. Agents that can be safely applied to the skin are called antiseptics. If you go to the pharmacy you will see many antiseptics that are available without a prescription from a physician. Antiseptics are not considered safe for internal consumption. In some cases iodine is used to kill bacteria on the skin prior to making a surgical incision. Soaps used for scrubbing by medical staff often contain iodine. Alcohol is used as an antiseptic to disinfect skin in an areas prior to insertion of a hypodermic syringe. There are fortunately many chemicals that can be taken internally and that are used to treat infectious diseases. The term antibiotic is used todescribe a substance that is produced by a microorganism and that kills or inhibits the growth of other microorganisms. Penicillin for example is produced by the fungus Penicillium and prevents the growth of pathogens like Staphylococcus. Today we use the term antimicrobic rather than antibiotic