Surface Disinfection

Introduction

Disinfection is a very important part of many jobs, especially those in laboratories or clinical settings. Good sterilisation techniques used alongside good cleaning help to reduce the risk of infection and prevent illness and disease spreading.

Pathogenic organisms are the cause of disease and infections. Due to this, there must be measures that allow the control of organism levels, to prevent and control the occurrence of disease. When looking at means in which to do this, surface disinfectants are a good starting point. Disinfectants, as a cost-effective and a preventative technique, are necessary in the community, especially where sterile environments are vital. With between 648000-1700000 people falling ill in the USA each year due to nosocomial infection ^{CITATION MPM15 l 2057 (1)} there is an immediate need to improve and research into surface disinfectants, to find a key way to reduce pathogenic levels and begin to tackle the high level of disease.

The definition of a disinfectant is ‘lt;i>substances used to control, prevent, or destroy harmful microorganisms (i.e., bacteria, viruses, or fungi) on inanimate objects and surfaces.’lt;sup> CITATION Gle08 l 2057 (2)

Surface disinfectants work on this basis, under two main categories& oxidising and non-oxidising disinfectants. Oxidising disinfectants such as& sodium hypochlorite and peracetic acid generally attack the cellular material of pathogenic organisms by oxidising the cell membrane to stop their functional abilities and prevents reproduction. ^{&CITATION Hol16 l 2057 (3)}

Most oxidising disinfectants contain chlorine and oxygen molecules due to their strong oxidising properties. These properties are a factor in the lysis of a pathogen and ultimately its death. Many oxidising surface disinfectants are found in household cleaning products, such as handwash. ^{CITATION Bou15 l 2057 (4)}

Aldehyde surface disinfectants, like glutaraldehyde and ortho-phthalaldehyde are examples of non-oxidising disinfectants. They generally have large bactericidal properties, along with sporicidal and fungicidal abilities, which is not common in most other surface disinfectants. ^{&CITATION Bou15 l 2057 (4)} These types of aldehyde disinfectants have guidelines to be used, as they can be harmful to health, with glutaraldehyde linked to asthma ^{CITATION Bou15 l 2057 (4)}. According to the CDC Guideline for Environmental Control 1981, both glutaraldehyde and ortho-phthalaldehyde must only be used for five minutes at temperatures 25˚&C and 35˚&C in an instrument that is able to maintain the temperature of the disinfectant solution ^{CITATION Wil08 l 2057 (5)}.

Alcohol disinfectants can be used& however they are better as an antiseptic, as they work effectively on living tissue. Normally, they are combined with another material such as water or dodecanoic acid to increase their efficiency of cell death ^{CITATION Bou15 l 2057 (4)}. Alone, alcohols can only denature Gram Negative bacteria and have no sporicidal or fungicidal abilities. Added to dodecanoic acid, alcohol disinfectants are able to denature a wide range of bacteria, and at a contact time of ten minutes at high concentrations were effective against some spores ^{CITATION Bou15 l 2057 (4)}.

Prior to the 1981 amendments of the Guideline for Environmental Control, an alcohol-formaldehyde solution was used as a surface disinfectant. This has now been removed as a recommended product due to it illustrating irritant and toxic properties ^{CITATION Wil08 l 2057 (5)}. It is necessary to monitor the effects of prolonged exposure to the chemicals and then to adjust usage of those chemicals accordingly.

For health reasons concentration needs to be monitored carefully. Concentration is an important factor in the efficiency of the disinfectant. Some chemicals may have a high efficacy and high concentrations, but could cause harm to the person using the chemical or even cause damage to the surface it is being applied to, but when too dilute the bactericidal properties may be lost ^{CITATION Gle08 l 2057 (2)}. Therefore, a safe medium must be found in order to effectively use the product without risking the health of those who will be in contact with it.

Alongside health precautions, there are other factors that are vital when looking at the efficiency of surface disinfectants. The application and storage has a strong influence on whether they are used outside of their experimental testing. The application process must be time effective as well as produce bactericidal effects. When applying the disinfectant optimum contact time should not be too long as that would be inefficient, especially in a hospital environment. In addition, if the solution is highly volatile and the surface must be soaked for an extended period of time, it would also be useless. If a solution cannot be stored easily, or has a short shelf-life, it is unlikely to be used as it would cause too many problems.

Most importantly, a consideration that must be looked at is the cost price. A surface disinfectant must be effective as well as cheap as hospitals, for example, need to keep a constantly sterile environment and cannot be using expensive products. This is why easily diluting products are more desirable when selecting a disinfectant ^{CITATION Gle08 l 2057 (2)}. Many disinfectant products in use began centuries ago and have been developed to produce more effective solutions to contaminants.

Early History

Surface disinfection has a long history spanning centuries. Ever since bacteria were discovered scientists have been finding ways to combat them. Over time, new technologies have been developed and disinfection became more advanced.

In 1799, Charles Tennant produced a large quantity of bleach cloth, as he had discovered bleaching powder (chlorine and slaked lime) and its disinfectant properties. The cloth was popular as it was easier to use and transport rather than chlorine, which had been in use previously, however the cloth was unstable and also contained inert material. Bleaching cloth remained the main household disinfectant until the 1920s when Clorox Chemical first produced bottles to give to local retail stores^{. CITATION Wal05 l 2057 (6)}

Frederick Calvert, a chemist studying in France, worked with carbolic acid from 1835 to 1846 and was the first to discover the disinfectant properties of carbolic acid (phenol). He also introduced the use of phenol for the use of embalming& preserving human remains to prevent decomposition. Following Calvert’&s discovery, German physician, Fredrich Kuchemeister was the first to use pure phenol in the dressing of wounds.

In 1865, Jules Lemaire was the proposed the idea of phenol being used in surgeries, he wrote about how phenol can be used to prevent infection and even recommended cleaning walls and surrounding of sick rooms and theatres with phenol, however Britain’&s surgeons did not share the same enthusiasm for this idea and so ignored the development taking place in France. However after much persuasion from Calvert, an article was reported on the benefits of phenol in treating sewage was published in a newspaper. Joseph Lister was initially working with a carbolic acid spray but modified his technique by covering wounds with phenol soaked dressings. ^{CITATION Lis72 l 2057 (7)} Antiseptic surgeries were transformed in to aseptic surgeries, and with the increase of aseptic techniques the uses of phenol become less important.

Jean Le Doyen proposed that hospital chambers and surgeries should have either a solution of nitric acid and ceruse or carbonate of lead and eater solution applied in each of the chamber vessels. He also suggested that cloths should be soaked in one of the solutions and applied to several places of the hospital buildings, to remove impurities, due to the solutions having disinfecting properties. ^{CITATION Jea47 l 2057 (8)}

Sodium hypochlorite replaced the potash solution (aqueous potassium), in 1820. It was discovered by Labarraque and was much more economical. Sodium hypochlorite solution was known as ‘&Eau de Labarraque’& which had many uses as a disinfectant and bleaching agent. Sodium hypochlorite is unaffected by hard water and can target a wide range of microorganisms. ^{&CITATION Cla07 l 2057 (9)}

Chlorine dioxide was discovered by Humphrey Davy in 1811 and is now a powerful disinfecting agent of water. Chlorine dioxide is fast acting and is effective as a disinfectant on skin, food and can also sterilise instruments and glassware.

Hypochlorite was the standard product of the British Pharmacopeia until 1963 for burns, despite chlorine dioxide being much less of a skin irritant and is also less toxic. However the application of chlorine dioxide to the skin was not practical as the gas needed to be activated with chlorine before application, this is why it was not widely used in World War 1.

Jacques Thenard then discovered hydrogen peroxide in 1818, which he named ‘&oxygenated water’&. It was primarily used to bleach straw hats& however it now has many other uses. Hydrogen peroxide also transformed low - temperature sterilisers, which were time consuming and used ethylene oxide which is carcinogenic. In 1996, Advanced Sterilization Products introduced a new instrument used in hospitals which used hydrogen peroxide. Hydrogen peroxide is used in the food industry as it is used to disinfect products and packaging prior to filling. It can also be used as a disinfectant to treat inflamed gums and to remove excess microbial growth in water systems. ^{CITATION Dav12 l 2057 (10)}

Until 1960, peracetic acid had little use& however from then it has been widely used in the food processing industry. It is the only agent which has been able to replace glutaraldehyde in the sterilization and disinfection of instruments in both the medical and dentistry fields. It is widely used due to the fact it can be used in low concentrations and temperatures.

Quaternary Ammonia Compounds (QAC) were first formed in 1973 by condensing 1,4-dihao-2-butane with 1,4-bis-dimethylamine-2-butane, it was then discovered in 1975 that it was a highly effective micro biocidal agent and its effects were not destroyed or effected by non-ionic emulsifiers. ^{CITATION Har75 l 2057 (11)}

In the last 40 years it has been discovered that many chemicals used as disinfectants, do not destroy bacterial spores but only prevent germination of spores. This had led to many other methods for disinfection to be investigated. ^{&CITATION Coo83 l 2057 (12)}

Current Uses

There are many different types of sanitation and disinfectant products currently in use and they have different bases and a cover a variety of situations. Multiple sterilization techniques are advised, especially in clinical settings. The most common medical sterilisation techniques include& irradiation, hydrogen peroxide, steam and ethylene oxide and formaldehyde.

Traditionally, the most common type of sterilization used was steam sterilization& this was due to the majority of medical tools being metal and therefore able to withstand high temperatures. This is changing now as more medical equipment is being made of cheaper alternatives, such as plastic. These need a much lower sterilisation temperature and therefore a different technique. ^{&CITATION NOH15 l 2057 (13)}

Steam sterilisation is still the preferred technique when possible due to it high reliability and consistency. There are also very few micro-organisms that can survive the high temperatures resulting in a very safe and cost effective sterilisation treatment. The moist heat produced through steam sterilisation is specifically designed to denature enzymes and proteins while causing them to irreversibly coagulate. Heat has been known for a long time as one of the most effective ways of inactivating and destroying micro-organisms. Steam sterilisation is used wherever possible, on both critical and semi-critical medical equipment which is moisture and heat stable. ^{&CITATION NOH15 l 2057 (13)}

Plastics are not commonly moisture or heat stable. This means they are not able to undergo steam sterilisation. Many new and improved sterilisation techniques are being worked on due to irreversible damage being caused to plastics using the older techniques. One technique built upon the earlier use of hydrogen peroxide and less thermally stable materials can be stabilised by hydrogen peroxide gas plasma. In this technique the item is placed in a chamber and after the air has been removed by a vacuum, the hydrogen peroxide gas is inserted. This is then also removed by the vacuum. This process works by inactivating micro-organisms by hydrogen peroxide gas and the free radicals formed inside the chamber. This method is compatible with over 95% of all medical devices and materials tested. ^{CITATION AMa14 l 2057 (14)}

Plastic, due to low cost, is becoming a much more common material in medical equipment, which means newer and improved sterilisation techniques are going to be required in the near future. This is due to many plastics reacting differently to different forms of sterilisation and each piece of medical equipment is made up of a number of different components.

Autoclaving is a laboratory favourite for sterilisation. An autoclave is an airtight machine in which the air can be removed, usually by a vacuum, before steam is allowed to enter the chamber. The chamber is then kept at a high heat and pressure, before the steam is removed to dry any laboratory equipment. Any microbes or bacteria caught inside the autoclave machine are destroyed by either dehydration or they are denatured due to the high temperatures and high pressure. ^{&CITATION SLy16 l 2057 (15)}

Ethanol and isopropanol are commonly used in laboratories to sterilise surfaces which are not possible to autoclave, such as work benches and stools. Ethanol and isopropanol are diluted and are sprayed directly onto the surface. They evaporate very quickly but when diluted with water are able to denature proteins that they come into contact with. They are very good at killing microbial pathogens but are virtually useless if spores have been released. ^{&CITATION WSo02 l 2057 (16)}

Many medical and clinical centres, particularly in the USA will reuse single use products as they believe sterilisation of these means that they are able to be reused without causing any problems. This is a controversial plan but was initially brought in as a cost saving technique. If these items are sterilised and disinfected according to the guidelines it should be safe however, reuse of these items carries risk and the FDA (Food and Drug Administration) are cracking down on the reuse of single use medical items.

Clothing worn in clinical settings and laboratories also has to be sterilised as bacteria can be passed onto sterilised equipment otherwise. This is why laboratory coats and scrubs are not allowed to be worn before entry to the lab, the ward or theatre. This is also why scientists and anyone working in a clinical setting will wear gloves or regularly wash their hands& to limit the spread of bacteria and ensure everything is kept as sterile as possible.

Problems Facing Surface Disinfection

Surface disinfection techniques and the chemicals that are utilised work effectively in many different situations however there are still problems that need to be solved.

One of the most prominent problems in the medical profession is the presence of nosocomial infections. Bacteria and subsequent infections can be transferred from patient to patient via the use of contaminated medical equipment. This can be done by the patient in direct contact with the equipment or by medical practitioners’& gloves touching the equipment and surroundings. Patients with immunocompromised diseases or patients who are seriously ill are particularly susceptible to infections. A further problem with incomplete surface disinfection in this context is the rising occurrence of antibiotic and multi-drug resistant bacteria, including Mycobacterium tuberculosis and Staphylococcus aureus. ^{&CITATION Gon15 l 2057 (17)}The danger of these infections means that limiting the spread of them is critical to patient care. Furthermore, these types of infections, also known as multi-drug resistant gram negative bacteria (MRGN) have limited therapeutic options available and as such finding suitable treatments can be difficult. If the pathogen becomes even more resistant then patient mortality rates may increase. One way to limit the danger of MRGNs is to find effectual ways of limiting transmission. ^{CITATION Rei14 l 2057 (18)} This would mean that fewer patients contract the pathogen and require treatment, which in turn may slow the development of their resistant capabilities.

Most disinfectants are ineffective against bacterial spores due to their remarkable resistance, for this reason, most novel disinfectants are aimed at not only destroying the bacteria present on surfaces, but also the bacterial spores that can remain on surfaces for several months even in the harshest of conditions. Spores are rich in disulphide bridges and the presence of calcium dipicolinate in several layers of their outer structure pertain to their ability to withstand changes in temperature, pH and nutritional deficiencies ⁽²⁶⁾.

The infections associated with ineffective surface disinfection is not just relevant in hospitals but in a number of other institutions including but not limited to schools, day care centres, restaurants and nursing homes. This could impact on the health of children and the elderly whose immune systems are perhaps not as strong as an average healthy adult. These groups are vulnerable to E. coli and can develop haemolytic uremic syndrome which can lead to serious kidney damage and in extreme cases death. ^{&CITATION MRy14 l 2057 (19)} This illustrates how important effective surface disinfection is and how ongoing research into this area is needed in reference to health care.

The importance of surface disinfection is not limited to just health care but a range of workplaces including laboratories and food processing companies. Any matter that may be defined as out of place on a solid surface are referred to as soils. There are many different types of soil including organic, mineral and the aforementioned bacterial. All of these may interfere substantially with laboratory processes and alter results of any experiments being conducted. In the food industry contaminants in high enough levels can have damaging effects to consumers and may be a breach in regulations. There are many type of cleaning agents however no one agent has the ability to remove all the soils from a surface. There are many factors for this including soil type and composition, surface structure and the adhesive strength of the soil on a variety of surfaces. ^{&CITATION YTo13 l 2057 (20)}

A further problem that can be identified concerning the development of new disinfectants is that whilst they show promising results in the laboratory and are easily reproducible it can be difficult to scale the technique to a larger environment. Application times and ease of use of new surface disinfectants will be relevant in the creation of new products and techniques. ^{&CITATION YTo13 l 2057 (20)} If disinfection takes a long time and is complicated then this could be counted against the effectiveness of the technique.

Ultimately, surface disinfection is relevant in many ways and this is one area that needs to be constantly undated to compete with the mutation of pathogens and to ensure the health of the populace.

New Developments

Disinfectants are constantly becoming less effective as the microorganisms adapt and evolve new ways of becoming resistant to the active ingredients in the product. For this reason, lots of research has taken place to create novel disinfectants and practices that can replace or enhance the current products used.

Nosocomial infections often arise due to bacterial spores present on most surfaces. Disinfectants are generally very good at eradicating live pathogenic bacteria, but few are effective at eliminating and removing the dormant bacterial spores. ⁽²⁴⁾ A study completed and published in 2012, aimed at testing a potential sporicidal disinfectant to fight bacterial spores and nosocomial infections ⁽²⁶⁾. Most disinfectants such as quaternary ammonium compounds are more sporostatic that sporicidal and this is particularly true for the concentrations that they are used in. Chlorhexidine, for example, is used at a concentration of 0.05% and is not sporicidal at this concentration. However, if applied at a high temperature, it was found to become sporicidal ⁽²⁶⁾.

The disinfectant in question was Akwaton, a polyhexamethylene-guanidine hydrochloride-based substance (PHMGH). The efficacy of this compound was tested against Bacillus Subtilis spores. The spores were developed and then suspended in distilled water and placed on different surfaces (stainless steel and glass) in order to obtain the log₁₀ reduction after exposure to Akwaton at varying concentrations. The minimum sporicidal concentration and the minimum sporostatic concentration were calculated using the broth dilution technique.

They found that the disinfectant was sporostatic at concentrations from 0.06 to 0.07% and is sporicidal at concentrations higher than or equal to 0.08%. The time taken for complete sporicidal activity is 8.5 minutes ⁽²⁶⁾. The sporicidal activity against the suspended spores (in distilled water) was linearly dependent to the concentration of PHMGH and contact time. Whereas, spores placed on stainless steel and glass were more resistant to the disinfectant and therefore, the linear relationship was not observed in these cases.

The concentration required to kill all spores placed on stainless steel or glass was calculated as 0.052%^ (w/v) for 90 seconds of contact and 0.36% (w/v) for 3 minutes of contact. The concentrations were lower for spores suspended in distilled water. Concentrations of 0.24% (w/v) and 0.44% (w/v) killed all spores within 3 minutes and 90 seconds respectively.

PHMGH is odourless, colourless, non-volatile and non-toxic to humans and so is much safer to use than many other disinfectants. Furthermore, the sporicidal activity of PHMGH is a two-step process: rehydration followed by inactivation. The rehydration step indicates why it is very effective as spores in their natural dehydrated state are very difficult to penetrate and therefore, eradicate.

In conclusion, the study has shown that PHMGH is a suitable novel disinfectant that could be potentially used in hospitals, laboratories and in the household.

Another prospective study carried out focused on the use of polyhexamethylene (PHMB), a newly developed wound antiseptic solution, with minimal side effects. The study was designed to demonstrate the efficacy of this antiseptic on non-healing wounds. The antiseptic was tested against Ringer’&s lactate solution (RLS) in terms of a reduction in wound size or closure of the wound completely. 31 patients were randomly split into a group of 15 and a group of 16, one receiving PHMB and the other RLS respectively. The results showed that 66.7% of patients being treated with PHMB were treated successfully and the wound had closed completely, compared to 43.8% of those receiving RLS treatment ^(24).

A particular nosocomial infection that is difficult to eradicate from hospitals is Clostridium difficile (C.difficile). Most infections caused by C.difficile are due to bacterial spores of the pathogen beginning to replicate.

Microwaves have also been shown to be effective at deactivating C.difficile and therefore reducing the risk of transmission in hospitals ⁽²⁵⁾. The spores of 15 C.difficile isolated from different host origins were exposed to microwave irradiation and conductive heating. The spores that were treated with 800W for 60 seconds showed inhibition of spore viability at 10⁷ CFU/ml ⁽²⁵⁾. Interestingly enough, the same study found that the conductive-heated spores did not have the same affect at the same time-temperature exposure. The study concluded that microwaves would be a simple and time-efficient tool to inactivate C.difficile spores.

Aldehyde based disinfectants are most commonly used in clinical practice, however, resistance has since been reported and has been known to cause undesirable side effects. A novel quaternary ammonium compound known as Virusolve+®& has been evaluated for its efficacy against Mycobacterium bovis, hepatitis C virus –& positive serum and hepatitis B surface antigen-positive serum. Cidex®&, an aldehyde-based disinfectant, was used as a comparison. The study found that M.bovis showed no signs of group after 10 weeks with either disinfectant. Virusolve+®& achieved a 10⁴-fold reduction from the initial 10⁶ HCV load under clean conditions (without red blood cells) for 20 minutes. Cidex®& however, managed to achieve this reduction under both clean and dirty conditions after both 10 and 20 minutes.

Furthermore, both disinfectants were able to eliminate hepatitis B virus infectivity after 20 minutes and showed equal mycobactericidal activity however, they showed comparable virucidal activity against HBV which was more effective under clean conditions ^(24). This study has provided insight into the effectiveness of ammonium based disinfectants and their ability to be used as a potential replacement for aldehyde based products. The results do show that the ammonium based disinfectant is more effective under clean conditions, which emphasises the need to general hygiene practices to be maintained in order for this disinfectant to be effective.

Additionally, a cheap and safe photosensitizer has been tested for its efficacy against enterovirus 71 (EV71) via photodynamic inactivation ⁽²⁷⁾. By altering light doses and photosensitizer concentrations, inactivation of EV71 among other enteroviruses was examined in vitro.

The study found that photodynamic inactivation of EV71 in suspensions occurred in a dose-dependent manner. They deduced that the optimal light dose for inactivation of EV71 as 200 J/cm² in the presence of methylene blue. At this dose, methylene blue was also able to inactivate a number of different enteroviruses such as the poliovirus. RT-PCR analysis showed that both the viral proteins and the genome were affected after photodynamic inactivation. The study concluded that methylene blue could be a novel and simple method to eradicate contaminated sources of EV71 among others to prevent transmission and infection ⁽²⁷⁾.

Conclusion

Surface disinfection has been a part of the scientific world for a long time and is a field which is constantly being reinvented. In recent years the developments have been vast and improvements are being discovered and developed continually. There are still problems that need answers including the effective eradication of spores and the emergence of resistant bacteria. However, with the use of PHMGHs and other new chemicals the survival of contaminants and pathogens is ever decreasing.

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