sterilization (microbiology) sterilization (microbiology) sterilization refers to any process that removes, kills, or deactivates all forms of life (particularly microorganisms such as fungi, bacteria, spores, and unicellular eukaryotic organisms) and other biological agents such as prions present in or on a specific surface, object, or fluid. sterilization can be achieved through various means, including heat, chemicals, irradiation, high pressure, and filtration. sterilization is distinct from disinfection, sanitization, and pasteurization, in that those methods reduce rather than eliminate all forms of life and biological agents present. after sterilization, an object is referred to as being sterile or aseptic. organisms growing on an agar plate applications foods one of the first steps toward modernized sterilization was made by nicolas appert, who discovered that application of heat over a suitable period slowed the decay of foods and various liquids, preserving them for safe consumption for a longer time than was typical. canning of foods is an extension of the same principle and has helped to reduce food borne illness ("food poisoning"). other methods of sterilizing foods include food irradiation and high pressure (pascalization). medicine and surgery joseph lister, a pioneer of antiseptic surgery. apparatus to sterilize surgical instruments (1914–1918) in general, surgical instruments and medications that enter an already aseptic part of the body (such as the bloodstream, or penetrating the skin) must be sterile. examples of such instruments include scalpels, hypodermic needles, and artificial pacemakers. this is also essential in the manufacture of parenteral pharmaceuticals. preparation of injectable medications and intravenous solutions for fluid replacement therapy requires not only sterility but also well-designed containers to prevent entry of adventitious agents after initial product sterilization. most medical and surgical devices used in healthcare facilities are made of materials that are able to go under steam sterilization. however, since 1950, there has been an increase in medical devices and instruments made of materials (e.g., plastics) that require low-temperature sterilization. ethylene oxide gas has been used since the 1950s for heat- and moisture-sensitive medical devices. within the past 15 years, a number of new, low-temperature sterilization systems (e.g., vaporized hydrogen peroxide, peracetic acid immersion, ozone) have been developed and are being used to sterilize medical devices. spacecraft there are strict international rules to protect the contamination of solar system bodies from biological material from earth. standards vary depending on both the type of mission and its destination; the more likely a planet is considered to be habitable, the stricter the requirements are. many components of instruments used on spacecraft cannot withstand very high temperatures, so techniques not requiring excessive temperatures are used as tolerated, including heating to at least 120 °c (248 °f), chemical sterilization, oxidization, ultraviolet, and irradiation. quantification the aim of sterilization is the reduction of initially present microorganisms or other potential pathogens. the degree of sterilization is commonly expressed by multiples of the decimal reduction time, or d-value, denoting the time needed to reduce the initial number n 0 to one tenth ( 10 − 1 ) of its original value. then the number of microorganisms n after sterilization time t is given by: n n 0 = 10 ( − t d ) =10^\right)}} . the d-value is a function of sterilization conditions and varies with the type of microorganism, temperature, water activity, ph etc.. for steam sterilization (see below) typically the temperature, in degrees celsius, is given as an index. theoretically, the likelihood of the survival of an individual microorganism is never zero. to compensate for this, the overkill method is often used. using the overkill method, sterilization is performed by sterilizing for longer than is required to kill the bioburden present on or in the item being sterilized. this provides a sterility assurance level (sal) equal to the probability of a non-sterile unit. for high-risk applications, such as medical devices and injections, a sterility assurance level of at least 10−6 is required by the united states food and drug administration (fda). heat steam