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The purpose for this literature review was to examine the literature currently available to the general public on the application of a range of disinfectants used within a microbiology laboratory in both the public e.g. hospital laboratories and the private sector e.g. university laboratories. This literature review was carried out on the effectiveness of disinfectants so that previous and current knowledge on the use of these disinfectants can be analysed. This will help give an insight into the subject area and help with the preparation and production of the final report based on the research being carried during the literature review and research project. The main purpose of the research project being conducted was to compare the effectiveness of a variety of disinfectants especially Trigene which has been endorsed for use in the microbiology laboratories of the Greater Glasgow and Clyde health board and that of Virkon which is currently used by the microbiology laboratory at the University of the West of Scotland.
The literature examined showed that the disinfectants used in clinical laboratories and any other area where microorganisms can cause a problem with cross-contamination, should be evaluated for their effectiveness against the range of organisms which might be encountered. It is an important requirement that the disinfectants being used are able to inhibit or kill the microorganisms quickly and by using the lowest concentration available. (Isenberg, 1985)
A study conducted by Kasthjerg et al (2010) which looked at the effects of a range of disinfectants on the expression of virulence genes present in the bacterium Listeria monocytogenes. This study showed that effects on the virulence gene in the bacterium could be linked to the chemicals found in the disinfectant with some causing an inhibition of the gene while others showed an induction of the gene
A disinfectant is a chemical which is widely used to eradicate a variety of microorganisms that are currently found in the samples received into a laboratory or are currently used within an educational setting for the teaching of microbiology to students.
Disinfectants can have any of the following chemicals as their main active ingredient: halogenated tertiary amines, chlorine containing compounds, phenols, quaternary ammonium compounds and peroxygen's. (Tyski et al, 2009) Thus the disinfectants can be divided into groups relating to the chemical present as the active ingredient and these groups will be discussed later in the report. It is important that certain criteria are met when classifying a chemical as a disinfectant, these include:-
That the chemical components of the disinfectant will not have an adverse effect on the health of the user and if any health issue is realised then appropriate action can be taken to remove this risk i.e. use PPE such as gloves or respiratory mask. (Severs & Lamontagne, 2002)
It. is also important that the disinfectant has the ability to render inactive or kill a wide range of microorganisms including viruses, bacteria and fungi. (Severs & Lamontagne, 2002)
It is also important that a disinfectant does not have an adverse effect when used on equipment.
The research conducted by Kim, Ryu & Beuchat, (2007) showed that the effectiveness of certain disinfectants can be diminished when they are in contact with biofilm surfaces. It is currently thought that there is very little resistance to the disinfectants used due to the presence of a variety of chemicals considered to have an antimicrobial effect in each disinfectant. (Kasthjerg et al, 2010)
Efficiency testing of disinfectants has been around for roughly 50 - 60 years ago. (Werner, 2007) In more recent years a working group was set up which set Standards which govern the microbial activity testing of chemicals used as antiseptics and disinfectants. (Werner, 2007: Tyski, S., et al, 2009) The introduction of these standards has allowed the efficiency tests to become more quantitative and produce lower margin of error. (Werner, 2007)
This group of disinfectants consists of chemical disinfectants which contain the chemical peroxygen and includes Virkon which is one of the disinfectants which will be evaluated during the research project being carried out. Virkon is available as a powder and is diluted for use by dissolving it in distilled water to give the required concentration. Virkon's method of action is through the combination of the chemicals chlorine, hydrogen peroxide and paraoxymonosulphate. (Alegente, G., et al, n.d.) These chemicals act by oxidation of the plasma membranes of microbial organelles. The effects of peroxygen disinfectants was investigated by a study conducted by Quilez et al, (2005) to discover what concentration of the disinfectant and time required for the disinfectant to be most effective when dealing with Cryptosporidium parvum oocysts.
The literature review conducted by Severs & Lamontagne, (2002) indicated that there was only a "moderate risk of irritation" to the user when the Virkon is in powder form. The Virkon may induce coughing, chocking or wheezing if inhaled while preparing the diluted disinfectant. However, when the powder has been diluted into a liquid form it is thought to cause no harm to the user's skin or eyes. (Severs & Lamontagne, 2002)
As the suggested research to be conducted is related to the efficiency of disinfectants then it was important to review current literature which gives an indication of the effectiveness on a range of microorganisms. From the literature it was shown that Virkon is effective when used as indicated against a wide range of microorganisms including Gram positive and gram negative bacteria, viruses, fungi and spore forming bacteria. The study conducted by (Severs & Lamontagne 2002) showed that these organisms were inactivated using a 1% solution of Virkon.
A study conducted by Gaparini et al, (1992) showed that Virkon was effective when used against spores which had been cultivated onto nutrient agar. This study also indicated that the effects of Virkon were quick acting; this could be attributed to the high concentration coefficient of the disinfectant.
Group 2 - Halogenated Tertiary Amine
This type of disinfectant is considered broad spectrum and biodegradable and is generally found in combination with detergents. (Health and Safety Executive, 2005). The halogenated Tertiary Amine group of disinfectants includes Trigene on which part of the research project is based. Trigene is available as a concentrated liquid or as a manufacturer diluted liquid. (Trigene Company) Trigene is also available in sachets which have been approved for use on submarines used by the Armed forces in the UK. (Severs & Lamontagne, 2002) The findings of the study by Severs & Lamontagne, (2002) showed that as with Virkon the use of Trigene was effective at rendering inactive viruses, bacteria and fungi when used in accordance with the manufacturer's instructions.
Health and safety tests were carried out on Trigene and the results have shown that the disinfectant poses a low risk to the users if accidently inhaled or ingested and there are no known health hazards with the use of Trigene. (MediChem international)
Quaternary ammonium compounds
This group of disinfectants is considered to be effective against most bacteria strains; however they are ineffective against viruses, bacteria which form spores and Mycobacterium. It is likely that this would not be an efficient disinfectant to be used within a clinical or university microbiology laboratory due to the risk of receiving samples containing spore forming bacteria, Mycobacterium species. The disinfectant can become inactivated by a low PH or the presence of organic material. (Health and Safety Executive, 2005) The mode of action for members of this group of disinfectants is that they damage the cell membrane which will result in cell leakage. (Ioannou et al, 2007) This study also showed that an increase in temperature increased the time taken to eradicate the bacterium.
The study done by, Kim, Ryu & Beuchat, (2007) showed that the efficiency of the disinfectant could be linked to the chemical structure of the Benzylalkonmium chloride's hydrophobic alkyl chain. It also showed that the presence of organic material (infant formula) can decrease the efficiency of the disinfectant.
Hypochlorite and other chlorine-releasing agents
This is a disinfectant which contains chlorine as its active ingredient, and an example of this disinfectant is Milton which is currently used to sterilise baby utensils. It is considered a broad spectrum disinfectant as it can inactivate or kill a range of bacteria and viruses. However, it is considered less effective against bacterial spores. As with the quaternary ammonium compounds this group of disinfectants has been shown to be inactivated by organic material and has to be prepared daily, this is due to the instability of the chemicals caused by concentration and temperatures at which the disinfectant is stored. (Health and Safety Executive, 2005) The hypochlorite disinfectant is provided in the form of Sodium Hypochlorite and it is commonly used within a clinical laboratory especially for the cleaning of equipment when recommended by the manufacture.
This group includes the disinfectant Hibetine which is currently used at the University of Glasgow and the active chemical is phenol. It has been shown to be a broad spectrum disinfectant which is effective against certain bacteria including Mycobacterium tuberculosis and some viruses, although shows no action against bacterial spores. The disinfectant is used with a combination of the phenolic chemical and a detergent. The advantages of using this type of disinfectant is that it is considered stable in undiluted form and organic material does not appear to have the same negative effect on the efficiency of the disinfectant as has been observed in other disinfectants..
Microorganisms' an introduction
The main purpose of conducting the research project was to observe the efficiency of disinfectants when used against a range of microorganisms. The microorganisms to be investigated include a Gram positive bacteria such as Staphylococcus aureus, a Gram negative bacteria such as Escherichia coli, a spore forming bacteria such as Bacillus cereus and a yeast e.g. Saccharomyces cerevisiae. The study conducted by Tyski, S., et al, (2009) used microorganisms which could easily be isolated from hospitals.
The study carried out by Ioannou et al, (2007) suggests that a common feature of bacteria especially staphylococcus aureus can acquire a plasmid which contains genes which will allow the bacteria to become resistant to certain antimicrobials.
The literature search carried out showed that the organisms which are commonly used in research to show the efficiency of disinfectants are commonly isolated from hospital patient samples. (Gasparini, et al, 1992)
Gram negative bacteria
Gram positive bacteria
The use of disinfectants in combating the spread of infections from bacterial spores from organisms such as C. parvum, Bacillus anthraxis, Clostridium difficile and bacillus cereus is important as these are the most difficult of all microorganisms to eradicate. (Quilez et al, 2005)
The literature reviewed has shown that disinfectants are an important part of the working environment of a laboratory as it is essential that the disinfectant has the ability to inactivate or destroy a wide range of microorganisms.
The study by (Severs & Lamontagne, 2002) showed that both Virkon and Trigene could be classed as efficient and broad spectrum disinfectants as they both killed a variety of microorganisms ranging from viruses (both enveloped and non-enveloped) to fungi and bacteria including spore forming species.
The study by Kasthjerg et al, (2010) deduced that the disinfectants which contained the peroxygen and chloride compounds decreased the virulence gene expression; however, the disinfectants containing the quaternary ammonium compounds encouraged the expression of the virulence gene.
The study conducted by Severs and Lamontagne, (2002) suggested that Both Virkon and Trigene were effective at eliminating the bacteria which could poses a health risk to divers but they felt that as the Virkon product had managed to eradicate more bacterial and viral strains than Trigene and that these effects were produced quicker with Virkon so the conclusion was that this product (Virkon) should be considered a better disinfectant and be recommended for use by divers.