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An antimicrobial is an agent that kills microorganisms or inhibits their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibacterials (commonly known as antibiotics) are used against bacteria and antifungals are used against fungi. They can also be classed according to their function. Antimicrobials that kill microbes are called microbicidal; those that merely inhibit their growth are called microbiostatic. Disinfectants such as bleach are non-selective antimicrobials.
Use of substances with antimicrobial properties is known to have been common practice for at least 2000 years. Ancient Egyptians and ancient Greeks used specific molds and plant extracts to treat infection. More recently, microbiologists such as Louis Pasteur and Jules Francois Joubert observed antagonism between some bacteria and discussed the merits of controlling these interactions in medicine. In 1928, Alexander Fleming became the first to discover a natural antimicrobial fungus known as penicillium rubens. He named the substance extracted from the fungus penicillin and in 1942 it was successfully used to treat a streptococcus infection.  Penicillin also proved successful in the treatment of many other infectious diseases such as gonorrhea, strep throat and pneumonia, which were potentially fatal to patients up until then.
Today, numerous antimicrobial agents exist to treat a wide range of infections.
Antibacterials or antibiotics are used to treat bacterial infections. The toxicity to humans and other animals from antibiotics is generally considered low. However, prolonged use of certain antibiotics can decrease the number of gut flora, which may have a negative impact on health. Some recommend that during or after prolonged antibiotic use one should consume probiotics and eat reasonably to replace destroyed gut flora.
The discovery, development and clinical use of antibiotics during the 20th century has substantially reduced mortality from bacterial infections. The antibiotic era began with the pneumatic application of nitroglycerine drugs, followed by a “golden” period of discovery from about 1945 to 1970, when a number of structurally diverse and highly effective agents were discovered and developed. However since 1980 the introduction of new antimicrobial agents for clinical use has declined, in part because of the enormous expense of developing and testing new drugs. Paralleled to this there has been an alarming increase in bacterial resistance to existing agents.
Antibiotics are among the most commonly used drugs. For example 30% or more patients admitted to hospital are treated with one or more courses of antibiotics . However antibiotics are also among the drugs commonly misused by physicians, e.g. usage of antibiotic agents in viral respiratory tract infections. The inevitable consequence of widespread and injudicious use of antibiotics has been the emergence of antibiotic-resistant pathogens, resulting in a serious threat to global public health. The resistance problem demands that a renewed effort be made to seek antibacterial agents effective against pathogenic bacteria resistant to current antibiotics. Possible strategies towards this objective include increased sampling from diverse environments and application of metagenomics to identify bioactive compounds produced by currently unknown and uncultured microorganisms as well as the development of small-molecule libraries customized for bacterial targets.
Antifungals are used to kill or prevent further growth of fungi. In medicine, they are used as a treatment for infections such as athlete's foot, ringworm and thrush and work by exploiting differences between mammalian and fungal cells. They kill off the fungal organism without dangerous effects on the host. Unlike bacteria, both fungi and humans are eukaryotes. Thus, fungal and human cells are similar at the molecular level, making it more difficult to find a target for an antifungal drug to attack that does not also exist in the infected organism. Consequently, there are often side effects to some of these drugs. Some of these side effects can be life-threatening if the drug is not used properly.
As well as their use in medicine, antifungals are frequently sought after to treat mold growth in damp or wet home materials. Sodium Bicarbonate (Baking soda) blasted on to surfaces acts as an antifungal. Another popular, professional antifungal (Serum) is often applied after or without blasting by soda and is a mix of Hydrogen Peroxide and a thin surface coating that neutralizes mold and encapsulates the surface to prevent spore release. Some paints are also manufactured with an added antifungal agent for use in high humidity areas such as bathrooms or kitchens. Other antifungal surface treatments typically contain variants of metals known to suppress mold growth e.g. pigments or solutions containing copper, silver or zinc. These solutions are not usually available to the general public because of their toxicity.
Antiviral drugs are a class of medication used specifically for treating viral infections. Like antibiotics, specific antivirals are used for specific viruses. They are relatively harmless to the host and therefore can be used to treat infections. They should be distinguished from viricides, which actively deactivate virus particles outside the body.
Many of the antiviral drugs available are designed to treat infections by retroviruses, mostly HIV. Important antiretroviral drugs include the class of protease inhibitors. Herpes viruses, best known for causing cold sores and genital herpes, are usually treated with the nucleoside analogue acyclovir. Viral hepatitis (A-E) are caused by five unrelated hepatotropic viruses and are also commonly treated with antiviral drugs depending on the type of infection. influenza A and B viruses are important targets for the development of new influenza treatments to overcome the resistance to existing neuraminidase inhibitors such as oseltamivir.
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Antiparasitics are a class of medications indicated for the treatment of infection by parasites, such as nematodes, cestodes, trematodes, infectious protozoa, and amoebae. Like antifungals, they must kill the infecting pest without serious damage to the host.
A wide range of chemical and natural compounds are used as antimicrobials. Organic acids are used widely as antimicrobials in food products, e.g. lactic acid, citric acid, acetic acid, and their salts, either as ingredients, or as disinfectants. For example, beef carcasses often are sprayed with acids, and then rinsed or steamed, to reduce the prevalence of E. coli.
Traditional healers long have used plants to prevent or cure infectious disease. Many of these plants have been investigated scientifically for antimicrobial activity, and a large number of plant products have been shown to inhibit the growth of pathogenic microorganisms. A number of these agents appear to have structures and modes of action that are distinct from those of the antibiotics in current use, suggesting that cross-resistance with agents already in use may be minimal. So, it is worthwhile to study plants and plant products for activity against resistant bacteria.
Copper-alloy surfaces have natural intrinsic antimicrobial properties and can kill microorganisms such as E. coli , MRSA and Staphylococcus. The United States Environmental Protection Agency has approved the registration of 355 such antibacterial copper alloys. As a public hygienic measure in addition to regular cleaning, antimicrobial copper alloys are being installed in healthcare facilities and in subway transit systems. Other heavy metal cations such as Hg2+ and Pb2+ have antimicrobial activities, but can be toxic to other living organisms such as humans.
Essential oils 
The antimicrobial properties of 21 essential oils and two plant essences were investigated against five food-borne pathogens. The maximum bacteriostatic concentration was 0.075%, with the oils of bay, cinnamon, clove and thyme being the most potent.
Antimicrobial Pesticides 
According to the Environmental Protection Agency, and defined by the Federal Insecticide, Fungicide, and Rodenticide Act, antimicrobial pesticides are used in order to:
- Control growth of microbes through disinfection, sanitation, or reduction of development.
- Protect inanimate objects (for example floors and walls), industrial processes or systems, surfaces, water, or other chemical substances from contamination, fouling, or deterioration caused by bacteria, viruses, fungi, protozoa, algae, or slime.
Antimicrobial Pesticide Products The Environmental Protection Agency (EPA) monitors products, such as disinfectants/sanitizers for use in hospitals or homes, in order to ascertain efficacy. Products that are meant for public health are therefore under this monitoring system—ones used for drinking water, swimming pools, food sanitation, and other environmental surfaces. These pesticide products are registered under the premise that, when used properly, do not demonstrate unreasonable side effects to humans or the environment. Even once certain products are on the market, the EPA continues to monitor and evaluate them to make sure they maintain efficacy in protecting public health.
Public health products regulated by the EPA are divided into three categories:
- Sterilizers (Sporicides): Will eliminate all bacteria, fungi, spores, and viruses.
- Disinfectants: Destroy or inactivate microorganisms (bacteria, fungi, viruses,) but may not act as sporicides (as those are the most difficult form to destroy). According to efficacy data, the EPA will classify a disinfectant as limited, general/broad spectrum, or as a hospital disinfectant.
- Sanitizers: Reduce the number of microorganisms, but may not kill or eliminate all of them.
Antimicrobial Pesticide Safety According to a 2010 CDC report, health-care workers can take steps to improve their safety measures against antimicrobial pesticide exposure. Workers are advised to minimize exposure to these agents by wearing protective equipment, gloves, and safety glasses. Additionally, it is important to follow the handling instructions properly, as that is how the Environmental Protection Agency has deemed it as safe to use. Employees should be educated about the health hazards, and encouraged to seek medical care if exposure occurs.
Both dry and moist heat are effective in eliminating microbial life. For example, jars used to store preserves such as jam can be sterilized by heating them in a conventional oven. Heat is also used in pasteurization, a method for slowing the spoilage of foods such as milk, cheese, juices, wines and vinegar. Such products are heated to a certain temperature for a set period of time, which greatly reduces the number of harmful microorganisms.
Foods are often irradiated to kill harmful pathogens. Common sources of radiation used in food sterilization include cobalt-60 (a gamma emitter), electron beams and x-rays. Ultraviolet light is also used as an antimicrobial in air and water purification systems, aquarium and pond maintenance, laboratories and food sterilization.
See also 
- "Antimicrobial - Definition from the Merriam-Webster Online Dictionary". Archived from the original on 24 April 2009. Retrieved 2009-05-02.
- M. Wainwright (1989). "Moulds in ancient and more recent medicine". Mycologist 3 (1): 21–23. doi:10.1016/S0269-915X(89)80010-2.
- Kingston W (June 2008). "Irish contributions to the origins of antibiotics". Irish journal of medical science 177 (2): 87–92. doi:10.1007/s11845-008-0139-x. PMID 18347757.
- Levy SB (ed) (1994) Drug Resistance: The New Apocalypse (special issue) Trends Microbiol 2: 341–425
- Challenges for the Development of New Antimicrobials — Rethinking the Approaches Bookshelf ID: NBK19843
- Copper Touch Surfaces
- A. Smith-Palmer, J. Stewart and L. Fyfe. Antimicrobial properties of plant essential oils and essences against five important food-borne pathogens. Letters in Applied Microbiology 1998. 26. 118-122
- Sanders, F. T. (2003). The Role of the EPA in teh Regulation of Antimicrobial Pesticides in the United States. Pesticide Outlook , 14 (2), 251-255.
- The Centers for Disease Control and Prevention. (2010). Acute Antimicrobial Pesticide-Related Illnesses Among Works in Health-Care Facilities--California, Louisiana, Michigan, and Texas, 2002-2007. JAMA , 304 (2), 152-154.
- The Antimicrobial Index - A continuously updated list of antimicrobial agents found in scientific literature (includes plant extracts and peptides)
- National Pesticide Information Center
-  - Overview of the use of Antimicrobials in plastic applications
- BURDEN of Resistance and Disease in European Nations - An EU-Project to estimate the financial burden of antibiotic resistance in European Hospitals