Cost effectiveness of mainstream bench cleaners against generic supermarket cleaners on the number of bacterial colonies killed

COST EFFECTIVENESS OF MAINSTREAM BENCH CLEANERS AGAINST GENERIC SUPERMARKET CLEANERS ON THE NUMBER OF BACTERIAL COLONIES KILLED.

HYPOTHESIS: - THE MAINSTREAM BRANDED CLEANERS WILL SHOW A GREATER PERCENTAGE DECREASE IN NUMBER OF BACTERIAL COLONIES KILLED THAN THE CHEAPER SUPERMARKET CLEANERS.

NULL HYPOTHESIS: - NEITHER CLEANER WILL PERFORM BETTER THAN THE OTHERS AND THEREFORE SHOW THE SAME PERCENTAGE DECREASE IN NUMBER OF COLONIES KILLED.

EXTRACT

The purpose of the investigation is to examine and compare a range of household work surface cleaners of different costs, in terms of their effectiveness at killing colonies of harmful bacteria on work surfaces. And whether or not you get a better cleaner for a greater financial expense. Bacteria are extracted from the surfaces in the investigations and examined against the total number of bacteria still present on the surface after one of the cleaner has been used on it. The 3 most expensive cleaners killed over 10% more bacteria than those at the cheaper end of the scale and showed almost twice the percentage decrease per penny. The reasoning behind a cleaner’s ability to kill bacteria tends to favour its composing chemicals, although the cleaners tended to be closely related to each other in terms of their ingredients. The 3 best performing cleaners contained alcohols, Benzalkonium Chloride and Tetrasodium EDTA compounds. This would suggest that these are the most favourable chemicals for an effective cleaning product in the household. The worst performing cleaner was based around sodium compounds and water, along with Alkyldimethyl Amine Oxide. Putting further evidence to the ingredients and chemical make up of a cleaning being key to its performance.

RATIONALE

Food poisoning is a major problem at the minute and is leading to rising numbers of hospital deaths. Deaths caused by MRSA (methicillin-resistant Staphylococcus aureus) and C difficile are continually increasing at alarming rates. C difficile is transmitted through poor surface hygiene and improper cleaning. Carried from surfaces when hands are not washed after use of the lavatory c difficile can get into foods and then into the human body. The C difficile spores cannot be destroyed by alcohol cleaners. Surfaces must be cleaned with bleach. MRSA does not pose a threat to the health of the public but has become prevalent in hospitals and in particular to vulnerable or debilitated patients. These include patients in intensive care units, burns units, surgical and orthopaedic wards because of its resistance to antibiotics (beta-lactams). Salmonella is generally associated with food poisoning and typhoid fever, it is transmitted from under-cooked poultry, eggs and food that has been cooked or frozen and not eaten straight away. The spread can be controlled by proper sanitation of food preparation surfaces.

Many cleaners being sold today contain very similar ingredients to each other, which often poses the question of why do some cleaners cost so much more than others? Moreover, do we just pay for the name on the bottle? On average mainstream big brand cleaners are almost twice as expensive as the supermarkets own brand. In a study of a supermarket, it was found that on average the big brand cleaners cost 74p more than the supermarket brand. It was also found that 3 out 5 cleaning products studied across the range, both supermarket own and main brands, contained Benzalkonium Chloride, Tetrasodium EDTA, Sodium Hydroxide and various forms of alcohol.

RESEARCH INTO POSSIBLE METHODS

METHOD 1 – RADIAL DIFFUSION

The Radial diffusion experiment will rely on the cleaners diffusing outwards radial over the agar in order to inhibit the growth of bacteria. In order to do this I will place a filter paper disc that has been soaked systematically in a cleaner on an agar plate that has already been inoculated with bacteria. This will be done after serial dilutions and a viable count. I will then repeat the same process with the other cleaners and incubate them all along with a control agar, which has been inoculated with bacteria but has not had a cleaner soaked disc placed into it, to show the bacteria in normality with any antibacterial products. To measure the inhibition I will take the incubated agars, place them over graph paper, and count the number of squares that are clear of bacteria to show how well the cleaner have worked in stopping bacterial growth.

Radial diffusion is a quick, easy and accurate method of measuring how a substance stops growth of bacteria. However, radial diffusion only measures the inhibition of growth. It is impossible to tell, without using a powerful microscope, whether the bacteria have been killed (bactericidal) or just been stopped from growing (bacteriostatic).

METHOD 2 – SURFACE CONTACT

Surface contact methods take a direct sample from the surface in question over its bacterial content. I will mark out study areas, of equal sizes, on the laboratory worktop. I will take a starting bacterial count of an area with a contact agar plate by placing a contact agar directly onto an untreated study area on the worktop. I will then take a cleaner and follow the given instruction prescribed by the manufacturer, and allow it to dry before taking a 2nd bacterial count by placing a 2nd contact plate onto the same study area. This process will be repeated in full for the other four cleaners. All the agars will be incubated and afterwards, I will count the number of bacterial colonies on the pre and post cleaner agars. Using these numbers, I will then generate individual percentage decreases for each different cleaner. The cleaner with the greatest percentage decrease has the greatest antibacterial properties.

The surface contact method accurately measures the amount of bacterial colonies killed by a given cleaner instead of just showing the inhibition of growth. It also uses the bacteria that the cleaners are designed to remove, therefore being objective in terms of the cleaners’ properties to kill bacteria. However, it also means that it is almost impossible to find a safe alternative to use, therefore it posses’ possible biohazard threats to health. As it is hard to determine what bacteria are on the worktops, it is unknown what possible risks the cultures pose after they have incubated. The method is also more time consuming than radial diffusion.

METHOD 3 – SWABBING

Another method that can be used is to use a cleaner to clean a workbench. A swab will be taken, before and after the addition of the antibacterial spray and the percentage decrease in the bacteria can be found by counting the number of bacteria before and after the spray has been used.

This is a real life situation and examines the effect on bacteria found on workbenches. These include, salmonella, Escherichia coli (E.Coli) O157:H7, Clostridium perfringens and Campylobacter jejuni. Bacteria are a common cause of food borne illness. In the United Kingdom, during 2000, the individual bacteria involved in causing food poisoning included; Campylobacter jejuni 77.3%, Salmonella 20.9%, Escherichia coli O157:H7 1.4%, and all others less than 0.1%.

Campylobacter jejuni is a species of curved, rod-shaped, non-spore forming, Gram-negative microaerophilic, bacteria commonly found in animal faeces. It is one of the most common causes of human food poisoning in the world but is rarely life threatening. It has been linked with subsequent development of Guillain-Barré syndrome (GBS), which usually develops two to three weeks after the initial illness. It commonly associated with poultry and naturally colonises the GI tract of many bird species. Contaminated food is a major source of isolated infections, with incorrectly prepared meat and poultry normally the source of the bacteria.

Salmonella is a genus of rod-shaped Gram-negative enterobacteria that causes typhoid fever, paratyphoid fever, and food borne illness. Salmonella species are motile and produce hydrogen sulphide. Other salmonellae are frequent causes of food borne illness, especially from poultry and raw eggs and more generally from food that has been cooked or frozen and not eaten straight away.

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Escherichia coli O157:H7 is an enter hemorrhagic strain of the bacterium Escherichia coli and a cause of food borne illness. Based on a 1999 estimate, there are 73,000 cases of infection and about 60 deaths caused by E.Coli O157:H7 each year. Most illness has been associated with eating undercooked, contaminated ground beef, drinking unpasteurized milk, swimming in or drinking contaminated water, and eating contaminated vegetables.

Clostridium perfringens is a Gram-positive, rod-shaped, anaerobic, spore-forming bacterium of the genus Clostridium. C. perfringens can be found as a normal component of decaying vegetation, marine sediment, the intestinal tract of humans and other vertebrates, insects, and soil. Some strains of C. perfringens produce toxins, which cause food poisoning if ingested. In the United Kingdom and United States, they are the third most common cause of food-borne illness, with poorly prepared meat and poultry the main culprits in harbouring the bacterium. It is often heat-resistant and can be detected in contaminated food and faeces.

This is more realistic than using a safe alternative such as E.Coli and S. Albus, which are the most common types of bacteria allowed in School and College Laboratories (Level 2), but are not repetitive of bacteria found as a whole.

Viable Count

Large organisms can be counted easily by sampling or direct observation, but this method is not appropriate for organisms as small as bacteria, which are not as easy to see except with very good microscopes. Even then, a live bacterium cannot be distinguished from a dead one just by looking at it. Counting methods often involve the use of microbial growth rather than direct counting. The large numbers of individuals involved also creates difficulties, for example if a sample from a bacterial colony is inoculated into nutrient broth and incubated overnight in optimum conditions, approximately 108 organisms will grow per cm3. A drop with a volume of 0.05cm3 will contain about 5 million cells – far too many to count accurately. In order to estimate the number of micro-organisms in a sample therefore, it is necessary to dilute the sample until small numbers are reached, then to count, and finally to multiple the count by the dilution factor to arrive at an estimate of numbers.

Viable count gives an accurate live count of the number if bacteria in a sample. However, it is a very time consuming process and uses a lot of equipment and resources. Percentage errors are very high if I were to pipette incorrectly at any stage. This is a into the effectiveness of cleaners on KILLING bacterial colonies, therefore I need to know whether or not a cleaner has actually killed the bacteria (bacteriosidal) rather than just stop it growing(bacteriostatic). If a cleaner is bacteriostatic then over time the bacteria will be able to begin to grow again once the cleaners’ effects have worn off. Meaning that later on, without anyone having used a surfaces bacterium will be able to contaminate food again and enter the food chain. Therefore, the ‘surface contact’ method is most suitable for my experiment.

TRIAL

In the trial, I will investigate the most effective way of transferring bacteria from the work surface in to the agar for culturing. I will take swabs directly from the workbench and then onto an agar plate and compare them with placing contact agar plates onto the workbench directly. I will first mark out areas of identical sizes to take the bacterial samples from, and then soak a cotton swab in sterile saline for a standardised period of time e.g. 10 seconds. I will then drag the swab over the neck of the bottle a standardised number of times to remove excess e.g. 5 times. I will then take a thorough swab of the sample area, ensuring a swab all the area before then swabbing the bacteria onto an agar plate for culturing. After sealing the agar plate in four places, I will then add a standardised volume of 1 of the cleaners and wipe it over a similar study area, next to the first area used, and wipe it in with a clean and dry cloth until it is dry. This is to test the methodologies behind adding the cleaning products are also sound. I will finally soak a new swab for the standardised time and remove the excess using the same techniques before taking a further swab of the cleaned area and swab it onto a second agar plate for culturing. To compare the effectiveness of this technique with a technique of using contact agar plates, I will follow a very similar method but replacing the saline cotton swabs with contact agar plates. I will take a first contact plate sample from a fresh area before sealing the agar. I will then add cleaner to a second fresh area, wipe it down as before, and finally take the second contact agar sample from the cleaned area. I will repeat both techniques a further 4 times and incubate all the plates for 48 hours before counting all bacterial colonies, before and after the addition of the cleaner. Using these numbers, I will generate percentage decrease to determine which technique produced percentages that are more consistent.

VARIABLES

TIME OF INCUBATION

Bacteria need warmth, nutrients and time to grow at their optimum rate. I will control the time that all the agars are incubated for because if an agar is incubated for longer than the others are then they have the opportunity to grow better than the others do. Whilst the others have been removed, those still being incubated will still have better warmth to grow in. this will mean that more bacteria will grow and compound the results. In order to control this I will incubate all the agars for the same length of time (48 hours). I will put them all in at the same time and remove them at the same time.

CONTACT TIME ON SURFACE

The contact time on the study surface should be controlled because if an agar remains in contact with the study surface for a longer period than others do, then it is given the opportunity to gain more bacteria from the surface. If the starting agar has more bacteria to start with and has had a longer contact time than the post cleaner agar than the percentage decrease could be compromised. If it does not have long enough than it will not pick up as much, showing a smaller percentage decrease, compounding results again. To control this I will place all agars onto surface for 10 seconds ONLY using a stop clock.

TEMPERATURE OF INCUBATION

I need to control the temperature that the agars are incubated at. If agars are incubated at different temperatures those incubated closer to 38oc will multiple at a faster rate than those either side of 38oc. Greater bacterial growth at the start will result in greater percentage decreases if the pre cleaner agars are incubated at higher temperatures than the post cleaner agars. If the post cleaner agar is incubated at a higher temperature to the pre cleaner than the percentage, decrease will be smaller, compounding the results. In order to control this I will incubate all agars at 25oc using a thermostatically controlled incubator.

I will repeat each cleaner a total of 6 times, by doing this I will be able to generate a correlation coefficient for the results and see if there is any sort of relationship to show that more expensive cleaners work better at killing bacteria on work surfaces.

TRIAL RESULTS

Anomalous results will be repeated and then excluded from consequent mean and standard deviation values, but left in the table of results, highlighted as an excluded value. The repeated value will be used in mean and standard deviation calculations and used to draw conclusions on results instead of anomalous. Anomalies will be attributed to uncontrollable factors in experimental equipment and procedure.

MODIFICATIONS FROM TRIAL

From my trial experiment, I can see that of the two techniques for sampling bacteria from the workbenches, taking swabs shows a more reliable source of data. The swabbed agar plates produced more successful cultures than those from contact agar plates, having used an identical cleaner throughout. However, from a total of 10 agar plates, only six produced bacterial growth. Even then, the results do not show any trends or correlation to each other. This may be because of the relentless and thorough cleaning that the laboratory workbenches under-go every night, when they are cleaned with strong disinfectant and alcohol cleaners, killing a large proportion of bacteria from the bench tops. Meaning there is little bacterial life to pick up onto the agars to culture. Therefore, I will alter the surface I am using and at the same time make the experiment even more realistic by using wooden chopping boards instead of lab workbenches to take bacterial samples. Due to the use of chopping boards, and in particular wooden ones, they are often full of scratches and gouges from knifes and other sharp utensils. These crevices would provide an optimum place for bacteria to thieve, where most household cleaning routines get into. The structure of wood also leaves it open to withholding water, providing the moisture that bacteria need to multiple. The cleaning products I have selected to use in the investigation are designed for kitchen cleaning, so I will use them where they were designed to be used, and on the kitchen apparatus which takes the most abuse and it’s the one thing which is most often blamed for the transmission of bacteria into food, the kitchen chopping board.

Swabbing: Mean % decrease = 66.7%

Standard deviation = 33 - VERY HIGH

(Higher possibility of anomalies)

Contact Plates: Mean % decrease = 97%

Standard deviation = 4.24 - LOW

Swabbing appears to be a more viable option from the trial results obtained. This may be because that contact plates simply cannot pick up the bacteria from the surface on their own. Whereas, with swabbing, the saline may provide moisture to bring the bacteria away from the surface and the swab itself penetrates better into the texture of the surface to pick up a great number of bacterial colonies, on average swabbing pick up more colonies than using contact plates. Contact plates picked up 47 colonies initially, whereas swabbing picked up over 60. This is probably because I can swab a larger area and be more thorough in doing it than when I am using contact agar plates. From experience, a greater number of bacteria picked up initially will mean a smaller percentage error. Because of this, in my main experimental phase I will pipette saline directly onto the area being studied before I swab as the areas appear to be dry and this may be causing fewer bacteria to be picked up initially.

MAIN METHOD

Using a removable marker or pencil, mark 10 study areas out on the chopping board. I chose to mark out 10 areas because, if I use the same areas for before and after a cleaner is applied, the initial swab may remove a large proportion of the bacteria in the area. Therefore, it will suggest a cleaner performs better than it truly does and therefore compound the results. I will use areas next to each other for the before and after swabs.
Using an auto pipette, add 3cm3 of saline and allow 10 seconds to soak in and spread. Using a cotton swab completely spread the saline over the whole area before firmly swabbing over the area in a set pattern and rolling the swab to pick up bacteria.
Streak the cotton swab over an agar plate in a set a pattern (see below) and transfer all bacteria from the cotton swab, rolling the swab to remove bacteria from the entire swab.
Take a cleaning spray, pipette 1cm3 of cleaner to the 2nd study area, and allow 10 seconds to soak. Spread the cleaner with a cotton swab, followed by the same swabbing technique as per before to pick up the bacteria.
Streak this swab onto a 2nd agar plate as before.
Repeat same process for other cleaning products; remember not to reuse the same location twice. If an area has already been used, there will not be as many bacterial colonies left in the area because of a previous cleaner being used on it. Therefore, any samples should not show any major differences between pre and post cleaner agar plates. Showing a smaller percentage decrease and compounding the results.
Label each agar with the product name, ‘pre’ or ‘post’ spray and the repeat number. I need to be able to identify which cleaner has been used for the agar plates in order to identify the appropriate percentage decrease in bacterial colonies.
Incubate all agars for 48 hours to allow for sufficient bacterial growth.
Count and compare bacterial colony numbers from pre to post spray agars and use them to calculate the percentage decrease for each cleaner.

Swab from Chopping Board Swab onto agar plate

RISK ASSESSMENT

BIOLOGICAL SAFETY LEVEL 1

Laboratory coats or gowns are recommended. Non-latex gloves should be worn if the skin on the hands is broken or a rash is present. Goggles or face shields should be used if splashes of microorganisms are likely.

GENERAL PRACTICES:

During periods of active manipulation of biologically active materials, access to the laboratory is limited or restricted. Doors to the laboratory are kept closed.
Hands are washed after viable materials are handled and before leaving the laboratory.
No eating, drinking, applying cosmetics, or handling of contact lenses is permitted in the work area. Contact lens wearers should wear goggles or face shields.
Food for human consumption cannot be stored in any laboratory refrigerator or freezer.
No mouth pipetting.
Sharps are disposed appropriately. Bio hazardous sharps containers are available for use in each laboratory.
Work practices are designed to minimize aerosols and splashes.
Work surfaces are decontaminated at least once a day during active use of a laboratory and after the spill of any viable materials. See
All cultures, stocks and regulated waste are decontaminated by an autoclave or appropriate chemical decontaminates.

Tissue culture waste (culture media) can be inactivated by placing it in a solution of 10,000-ppm hypochlorite for 8 hours. Sewer with copious water.
Tissue-culture contaminated pipettes can be placed in a solution of 2500-ppm hypochlorite for 8 hours before disposal by autoclaving or incineration.

BIOLOGICAL SAFETY LEVEL 2

The “General Practices” outlined for Biological Safety Level 1 also apply to the increased risk setting of Biological Safety Level II. Additionally, special practices are applied to ensure the increased risk does not result in injury or illness to students, faculty and staff. Blood borne pathogen protocols supersede Biological Safety Level II activities when human blood or body fluids are present.

SPECIAL PRACTICES

Individuals entering the laboratory are advised of the risks. Biological Safety procedures are incorporated into the standard operating procedures for the laboratory, and personnel are required to read and follow these procedures.
Traffic flow or movement is restricted when a biological safety cabinet is in use.
Procedures that are likely to produce an aerosol or splash should be conducted in a biological safety cabinet or if that is not feasible, a face shield should be worn. Examples of activities that might produce aerosols or splashes include. Centrifugation, grinding, blending, vigorous shaking or mixing, sonic disruption, opening containers of infectious materials whose internal pressures might be different than ambient pressures, and harvesting infected tissues from animals or embryonate eggs.
Biological safety cabinets should be used if either manipulating high concentrations of infectious material or large quantities.
Protective clothing is either disposed in the laboratory or laundered by the institution. It is never taken out of the laboratory by individuals.
Gloves are worn when hands might encounter potentially infectious materials, contaminated surfaces or equipment. Hands are washed following removal of gloves.
Contaminated sharps are handled with extreme caution:

Use of needles and other sharp objects is discouraged unless absolutely necessary for the procedure in question.
Do not recap needles—discard the needle and syringe in a biohazard sharps container.
Broken glassware is never cleaned up by hand. Instead, dustpans and brushes are used to collect the broken glass and it is disposed in a biohazard sharps container.

Materials contaminated with human body fluids are decontaminated by autoclaving and placed in a container with a cover that prevents leakage during storage, transport or shipping. Other potentially infectious waste is placed in a container with a cover that prevents leakage before decontamination by autoclave.
Laboratory equipment and surfaces are decontaminated routinely after work with infectious materials is completed and especially after any spill.
Animals not involved in the work are not allowed into the laboratory.
Safety training including identification of risks, safe handling and emergency procedures is required for all employees.
Medical surveillance:

Spills that might results in overt exposure are reported in the appropriate Accident/Injury form and medical evaluation, surveillance and treatment are provided. Records of exposures are maintained.
Individuals at higher risk for infection (e.g. immunosuppression) are not allowed in the laboratory. The responsibility for assessing each circumstance and establishing policies lies with the laboratory supervisor.
The laboratory supervisor is also responsible for determining whether appropriate immunizations or tests for the agents handled are available.

RESULTS

ANOMALOUS RESULTS

There were no visible in the 4 most expensive cleaners, this is supported by the low standard deviation values showing that the results were over a small range from the mean result. However, the cheapest ‘Tesco Kitchen Cleaner with Bleach (500ml)’ appeared to have an anomaly, ringed and highlighted in the table. The standard deviation was relatively large, meaning that there was a high possibility for anomalies in the results. The test was repeated for the anomaly and the repeat result placed into the results table.

CORRELATION CO-EFFICIENT

The equation to calculate the correlation co-efficient of a data set is:

r =

The correlation co-efficient of cost/cm3 Vs % decrease = 0.436076

At 3 degrees of freedom, the correlation co-efficient value ‘p’ is greater than 0.1 at 0.05 (5%) probability. Meaning that as the cost/cm3 increases the percentage decrease also increases. However, it is unlikely that a significant correlation will show in any tables or graphs. Because the sample size is so small, p values must be much closer to one to be significant when compared with larger samples sizes. Because the p value is so far outside the significant value given in the table of co-efficient it means that it is more likely that my results could be down to chance.

DISCUSSION

The scatter graph shows a general positive trend between the cost of cleaning fluid and its anti-bacterial ability. The three mainstream cleaners tended to outperform the two generic cleaners in terms of the percentage of bacterial colonies they killed when they were applied. Cif, Dettol and Mr. Muscle all killed over 90% of the bacterial colonies consistently across the sample with low standard deviation from 1% to 5%, meaning that the results were very close together and consistent. Whereas, Tesco’s' own cleaners were ranging in their performance, from around 55% bacteria killed to 100% with wide standard deviation, 5% to 20%. The correlation was very insignificant suggesting a very weak positive correlation, but I have accepted it as a valid result, which supports my hypothesis;

‘The mainstream branded cleaners will show a greater percentage decrease in number of bacterial colonies killed than the cheaper supermarket cleaners.’

The chemical formulation and contents of a cleaning product can be crucial in determining their performance in their function and purpose. The mainstream cleaners all contain a chemical called Benzalkonium Chloride, which the supermarket cleaners did not; Benzalkonium Chloride is a nitrogenous cationic surface-acting agent belonging to the quaternary ammonium group commonly used in disinfectants and anti-corrosion fluids. It is readily soluble in ethanol and acetone and can be used as a biocide and phase transfer agent. This may have had a significant role in the cleaners’ performance, and may be the bacteriosidal difference that makes the mainstream cleaning products better at their purpose than the supermarket formulations.

All the cleaning products have common ingredients, which suggest that overall the cleaners are not altogether chemically different and that their performance is down to slight differences and discrepancies in their contents.

ALCOHOLS

All the cleaners appear to contain alcohol of one form or another and it is well known and used for sterilising work surfaces, especially in schools and colleges in the form of ethanol.

Ethyl alcohol, at the concentrations used in most antibacterial preparations, kills bacteria by disrupting membranes and by denaturing proteins. Ethyl alcohol is miscible in water (that is, completely soluble). However, ethyl alcohol can also dissolve in the membranes of cells. These membranes are composed of lipids, compounds that do not dissolve readily in water. As the alcohol works its way into the membranes, it disrupts their structure and function. Membranes delineate the inside from the outside of the bacterial cell. When the membranes are disrupted, the insides of the bacteria can be lost. Ethyl alcohol can readily get into the bacterial cell because it can pass through the membrane. Once inside the cell in high concentration, it changes the normal solvent of the cell (which is primarily water). In this new solvent, composed of water and ethyl alcohol, proteins no longer fold properly and can be "denatured" (that is, they lose the structure that is necessary for them to have their natural function). Without proper proteins, cells cannot survive.

Ethyl alcohol is also toxic to humans at high enough concentrations. It's also the alcohol found in alcoholic beverages, so clearly low concentrations will not kill. Ethyl alcohol is not readily taken up through the skin, so unless we ingest it, it is hard to get dangerous doses of this chemical. Therefore, the combination of low toxicity to humans (when used properly) and high toxicity to bacteria (at the high concentrations in which it is used) makes ethyl alcohol a common choice.

BENZALKONIUM CHLORIDE

Benzalkonium chloride appears in all but the cheapest cleaner from this investigation, highlighting that it may be an effective component with antibacterial properties in the cleaners.

Benzalkonium chloride (alkyl dim ethyl benzyl ammonium chloride) is a mixture of alkyl benzyl dimethylammonium chlorides of various alkyl chain lengths. It is commonly used as an antiseptic and spermicidal. This product is a nitrogenous cationic surface-acting agent belonging to the quaternary ammonium group. The greatest bactericidal activity is associated with the C12-C14 alkyl derivatives. It has been considered one of the safest synthetic biocides known, and has a long history of efficacious use. However, conflicting studies cast doubt on its reputation for safety. Some products have been reformulated in light of this research, but it is still widely used in eyewashes, hand and face washes, mouthwashes, spermicidal creams, and in various other cleaners, sanitizers, and disinfectants. It is also used as an annual treatment for the elimination of bacteria in water within waterbeds.

Benzalkonium chloride is readily soluble in water, alcohol, and acetone. Formulation requires great care as Benzalkonium can be inactivated by certain organic compounds, including soap, and must not be mixed with anionic surfactants. Although newer formulations are more resistant to deactivation, as with any disinfectant, it is recommended that surfaces are rinsed well before disinfection.

The mechanism of bactericidal action is thought to be due to disruption of intermolecular interactions. This can cause dissociation of cellular membrane bi-layers, which compromises cellular permeability controls and induces leakage of cellular contents. Other bimolecular complexes within the bacterial cell can also undergo dissociation. Enzymes, which finely control a plethora of respiratory and metabolic cellular activities, are particularly susceptible to deactivation. Critical intermolecular interactions and tertiary structures in such highly specific biochemical systems can be readily disrupted by cationic surfactants.

Benzalkonium chloride solutions are rapidly acting anti-infective agents with a moderately long duration of action. They are active against bacteria and some viruses, fungi, and protozoa. Bacterial spores are considered to be resistant. Solutions are bacteriostatic or bactericidal according to their concentration. Gram-positive bacteria are generally more susceptible than gram-negative. Activity is not greatly affected by pH, but increases substantially at higher temperatures and prolonged exposure times.

EVALUATION

The experiment had certain limitations, which could be detrimental in the validity of my results and contribute to the increased probability of results due to chance.

It was difficult to collect bacteria from the chopping boards because bacteria colonise in cracks and gaps in surfaces, not on top. This meant that I only collected bacteria that were on top of the board or close enough to the surface to be picked up by the swab. To overcome this next time it may be viable to take a core sample of the board and segment it onto am agar plate to allow bacteria from all the way through the board to culture.

One of the uses of Benzalkonium Chloride is to make chemicals more fluid, because of this; it may be down to the cleaners primarily being liquid that the majority of the bacteria were killed. It would be appropriate to test the effect of domestic soap combined with water as well as water in isolation on bacterial colonies, to clarify whether the concept of liquids kills bacteria.

Many of the cleaners were almost identical in their contents and ingredients, making it difficult to draw scientific conclusions on which chemical complexes have better anti-bacterial properties. In future, it could be possible to use each of the chemical ingredients in isolation to get a true representation of the chemical differences between cleaners and their effect on their performance.

Surface cleaners are aimed at killing bacteria that contaminate food and cause infections and food poisoning in humans at body temperature (34˚c). I was unable to incubate at this temperature due to the college only having level 2 laboratory status throughout its science department, limiting their resources, including allowing them to culture ant incubate at temperatures up to 25˚c. Some of the critical human infection causing bacteria may not grow and culture at these temperatures. They may still grow after the cleaners have been applied, meaning that my tests and experiment were not subjective to the substances being used. In future, I will need to try to acquire the ability to incubate bacteria at 34˚c in order to get a truly subjective and real life test for the effectiveness of cleaners.

Swabbing the surfaces may not have transferred all the bacteria from the swab onto the agar plate after it had been used to swab the bacteria up from the chopping board, having a detrimental effect on the results of the investigation, showing inaccuracies to the true value. To solve this problem next time I could swab the chopping board as normal, but then soak the swab in sterile saline to remove all the bacteria into the saline and then, after mixing up the solution for 5 minutes, pipette out and spread an amount of the saline/bacteria solution onto the agar plates.