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Antimicrobial Disinfectant Formulations

Disinfectants are a class of antimicrobial chemicals which are used to kill microorganisms inhabiting non-living objects and surfaces; they are distinct from antibiotics and antiseptics which are employed to kill microorganisms living inside the body or on living tissues.  Disinfectants are widely used in industry, hospitals and domestically to ensure hygiene in the home setting.  An ideal disinfectant would be one which sterilises (eliminate 100% of microorganisms) with minimal toxicity to humans and animals and minimal damage to the surface being cleansed.  In reality, such a disinfectant does not exist and a balance is struck between effectiveness and practicality of use.  The choice of disinfectant employed generally depends on the degree of sterility required and the characteristics of the surface to be disinfected.

Disinfectants are available in many forms including physical factors (such as x-rays, ultraviolet radiation or heat) and chemical compounds (including alcohols, aldehydes, halogens, oxidising agents, phenolics and quaternary ammonium compounds) (McDonnell and Russell, 1999).  Phenol is one of the oldest known disinfectants and effective against most bacteria and enveloped viruses.  While phenol based disinfectants are generally safe, prolonged skin exposure may cause irritation.  Alcohols are less irritating and are effective bactericidals employed as surface disinfectants in hospitals and laboratories; however they do carry an ignition risk.  Halogens such as hypochlorites are amongst the most common disinfectants and are a cheap and effective solution for many situations.  Chlorine based bleaches have a wide spectrum of antimicrobial activity.  While toxicity is low, chlorine gas can be released during use and hypochlorites are corrosive to many metals.  Aldehydes are highly effective disinfectants however they can also be highly toxic and require special care in their application.  Gamage (2003) reviewed the different available antimicrobial formulations.

Staphylococcus aureus is a spherical, gram-positive coccus, bacteria which grows as clusters of cells.  Asymptomatic colonization of humans is common with 20-25% of the population carrying this bacterium on the skin or the lining of the nasal cavity (von Eiff et al, 2001).  S aureus causes many minor complaints including skin infections, pimples, boils, as well as more serious conditions including pneumonia, meningitis, food poisoning, toxic shock syndrome and septicaemia.  In addition S aureus is one of the most common causes of post surgical wound infection.  Diagnosis of S aureus infection involves Gram staining followed by enzyme tests to identify catalase, coagulase, DNase, lipase and phosphatase, characteristic enzyme constituents of S aureus.

Antimicrobial resistance is a major characteristic of S aureus.  Resistance to Penicillin is mediated by expression of the blaZ gene, which produces the penicillinase enzyme (Kernodle, 2000).  Penicillinase-producing strains of S aureus were first identified in the mid 20th century and penicillin resistance has gradually increased since with 40% incidence in the 1940's, 80% by the 1980's, and today only 2% of strains are sensitive to penicillin (Chambers, 2001).  Of particular clinical concern today is the emergence of MRSA (methicillin resistant S aureus), a major public health concern with mortality rates of between 20 and 40% (Crowcroft and Catchpole, 2002).  Methicillin was introduced in 1961 and the evolution of resistance to this semi-synthetic penicillin derivative was rapid, with outbreaks of resistant strains being reported in the same year.  Although methicillin is no longer used in the treatment of S aureus, MRSA remains a major health problem due to the resistance of this strain to multiple and diverse antibiotics.  Novel treatments have been proposed to try to prevent nasal colonization of S aureus in asymptomatic carriers including the use of bacteriophages as an antibacterial therapeutic (Fischetti, 2001), and vaccination as a potential future prospect for preventing S aureus infection (Fattom et al, 2004).

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