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Antimicrobial Agents

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*5/29/2012

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“Microorganisms are known to present health hazards due to infection or contamination. When microorganisms are present on the surface of a substrate they can replicate rapidly to form colonies. The microbial colonies form a coating on the substrate surface, which is known as a biofilm. Biofilms frequently consist of a number of different species of microorganisms which in turn can be more difficult to eradicate and thus more hazardous to health than individual microorganisms. Some microorganisms also produce polysaccharide coatings, which makes them more difficult to destroy.

Microorganisms attach themselves to substrates forming a biofilm comprising a "calyx" of polysaccharides and/or similar natural polymers as the affixing mechanism. Without this affixing point, the reproduction of the microorganism particularly bacteria cannot proceed, or is at least seriously impaired.

Biofilms form when microorganisms such as bacteria adhere to surfaces in aqueous environments and begin to excrete Extra cellular secretion, a slimy, glue-like substance that can anchor them to all kinds of materials such as metals, plastics, soil particles, medical implant materials and tissue. A biofilm can be formed by a single bacterial species but more often biofilms consist of several species of bacteria, as well as fungi, algae, protozoa, debris and corrosion products. Essentially, bacterial biofilms may form on any surface exposed to bacteria and some amount of water. Once anchored to a surface, biofilm microorganisms carry out a variety of detrimental or beneficial reactions (by human standards), depending on the surrounding environmental conditions.

Many anti-microbial agents that can destroy microorganisms which are present in a wide range of environments such as medical, industrial, commercial, domestic and marine environments are known. Many of the known anti-microbial agents have previously been included in compositions for use in various applications and environments.

The known anti-microbial agents and the compositions that contain these anti-microbial agents destroy microorganisms by a number of different mechanisms.

For example, many anti-microbial agents are poisonous to microorganisms and, therefore, destroy microorganisms with which they are contacted. Examples of this type of anti-microbial agent include hypochlorites (bleaches), phenol and compounds thereof, arsenene and salts of copper, tin and arsenic. However, such agents typically are highly toxic to humans and animals as well as to microorganisms. Consequently these anti-microbial agents are dangerous to handle, and specialist handling, treatment and equipment are therefore required in order to handle them safely. The manufacture and disposal of compositions comprising this type of anti-microbial agent can, therefore, be problematic. There can also be problems associated with the use of compositions containing this type of anti-microbial agent, particularly in consumer materials where it is difficult to ensure that they are used for designated purposes.

Herein, unless the context indicates otherwise, "toxicity" is intended to refer to toxicity to complex organisms such as mammals. References to "toxic" are to be construed accordingly.

Once the anti-microbial agents enter the environment they can affect the health of life forms that they were not intended to affect. Furthermore, the anti-microbial agents are often highly stable and can cause environmental problems for long periods of time.

Other known anti-microbial agents that are commonly used include organic and inorganic salts of heavy metals such as silver, copper or tin. These salts produce toxic rinsates, which can cause problems to the environment. For example, the rinsates of such salts are poisonous to aquatic life. Again, once the toxic compounds enter the environment they are not easily broken down and can cause persistent problems.

Other anti-microbial agents currently in use include antibiotic type compounds. Antibiotics disrupt the biochemistry within microorganisms, for example by selectively diluting solutions to destroy or inhibit the growth of harmful microorganisms. Although antibiotics are effective, it is currently believed that they may selectively permit the development of resistant strains of the species that they are used against. These resistant strains are then able to reproduce unimpeded by the use of known antibiotics. Thus, there is a growing concern that wide and uncontrolled use of antibiotic materials in the wider environment, as opposed to their controlled use in medical contexts, could produce significant long-term risks.

Another method of microbial control is the use of oxidising agents in materials, such as household bleach. Which can be based on hypochlorite or peroxides such as hydrogen peroxide These materials are effective in a wet environment for sterilization and cleansing. However, the materials do not provide long-term passive anti-microbial control and sanitisation. By "passive control" we mean that the substrate counters microbial infection on its own by some property within it even in a dry environment, so that it does not require a cleaning regime to be effective at controlling microorganisms.

Another method involves the use of materials such as quaternary ammonium compounds that act as lytic (bursting) agents for the microbial cells. This method has the disadvantage of not being effective against all strains of microorganism so that resilient colonies can develop that have a high degree of "survivability" to disinfection with quaternary ammonium compounds so that they need to be alternated in use. Additionally, these materials are highly water soluble so easily wash away or can easily contaminate moist materials in contact with them.”

[Schwarz and Falder, US Patent 8,178,484 (5/15/2012)]

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Copyright 2012 by Roger D. Corneliussen.
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* Date of latest addition; date of first entry is 5/29/2012.