Bacterial Resistance to Antibacterial Agents

A Research Paper by

Eli Balkin, Michael Domek, Michael Durisen, Alejandra Miller, Shirley Wang

Miami University, Oxford, OH
Natural Systems Fall 2002

Natural Systems 1 Fall, 2002 -Interdisciplinary Studies-Miami University

Abstract

As the first documented life to appear on earth, bacteria play a key role in the process of evolution. They are the oldest, the simplest, and contain numerous forms of life. A vast number of bacteria live in our bodies, performing a number of different functions. Some of these bacteria help us with digestion and the production of vitamins, others can harm us by causing illnesses. While we have immune systems that help us combat diseases, humans have also created artificial anti-bacterial agents to help us kill bacteria in their external environment.

When purchasing anti-bacterial agents there is the choice between a name brand and a generic brand. In the vast array of anti-bacterial agents, there are those that are offered and advertised from big companies, or name brands. There are also those anti-bacterial agents that claim to perform the same job, except they lack the fancy labels and marketing techniques, better known as generic brands. It was our desire to find out if the more expensive name brand is more effective in killing bacteria. Ultimately, this experiment is based on the question, which type of anti-bacterial agent kills bacteria better, the name brand or the generic brand.

Upon conducting our research, we have hypothesized that the name brands will kill the bacteria faster and more effectively than the generic brands. According to how thorough and how fast the anti-bacterial agents work, we believe that there will be a noticeable advantage to the use of name brand products. The experiment hopes to show a significant difference between the killing effects of each brand of anti-bacterial solutions. By the end of our experiment and research, we hope to have developed a better understanding of bacteria and the way anti-bacterial agents work.

 

Introduction

Bacteria are an important aspect in the existence of life on Earth. In fact, it was bacteria that first appeared here on Earth around 3.5 billion years ago (Campbell et al., 2002). Since then, bacteria have been essential to the survival of all other living creatures.

Bacteria are classified as prokaryotes, which are single cells that do not contain a nucleus. The three most common prokaryotic shapes are spherical (cocci), rod-shaped (bacilli), and helical forms. A bacterium’s structure is quite simple; it consists of a cell wall, a cell membrane, and a cytoplasm. The cell wall protects and shapes the cell and prevents osmotic bursting. The cytoplasm holds the hereditary material and at times the endospore. End membranes do not compartmentalize prokaryotic cells. However, invaginations of the plasma membrane may provide internal membrane surface for specialized functions. The prokaryotic genome consists of a single circular DNA molecule in a nucleoid region unbounded by a membrane. Many species also possess smaller separate rings of DNA called plasmids, which code for special metabolic pathways and resistance to antibiotics. Bacteria reproduce asexually by binary fission. Due to this mode of reproduction, genetic variation only occurs through mutation and gene transfer by transformation, conjugation, or viral transduction. Transformation occurs when genes are taken up from the surrounding environment. Conjugation occurs when genes are transferred directly from one prokaryote to another. Viral transduction occurs when genes are transferred between prokaryotes by viruses (Campbell et al.).

There is another diverse group of bacteria called archaeabacteria, which are prokaryotes that do not have a nucleus. They are considered a major group unto themselves. All other bacteria that do not fall into the category of archaeabacteria are called eubacteria. Archaeabacteria are more similar to eukaryotes than to bacteria in that their cell walls do not contain peptidoglycan, which is a component of each bacteria cell, but they do not have a nucleus, which eukaryotes have (Campbell et al.). There are three major groups within the archaeabacteria, methanogens, halophiles, and thermopiles (Wassenaar, 2002). Methanogens are anaerobic bacteria that produce methane. Methanogens are commonly found in sewage treatment plants, bogs, and the intestinal tracts of ruminants. Ancient methanogens are the source of natural gas. Halophiles are bacteria that depend on high salt concentrations and thus are commonly found in salt lakes or pools of seawater. The last group, thermophiles, is found in extreme temperatures such as hydrothermal vents and hot springs (Hampil, 1932).

There are about two thousand species of bacteria identified (Campbell et al.). A major reason for such a great number is that prokaryotes can live in a number of environments. They can be found from the upper atmosphere to the ocean floor, from the human gut to rocks a mile deep. According to William Whitman, a microbiologist at The University of Georgia, approximately 5x1030 prokaryotes share the planet with us. Of those, 3.9x1023 of them live in the human gut of all six billion of us. The vast majority of bacteria, however, live under land or under the sea floor. Ninety-two to ninety-four percent of all prokaryotes live hidden in the cracks and pores of rock and sediment, lacking sunlight and fresh air (Tenenbaum, 1998).

To deduce how many bacteria there are, Whitman opted for a sampling technique. He divided the world into representative habitats, such as forests, deserts, freshwaters, and shallow and deep ocean waters. Then he looked into literature for studies on the density of bacteria in each habitat. From there he multiplied the size of the habitat in milliliters, by the number of prokaryotes per milliliter to estimate the total number of bacteria in that habitat. The data also helped explain the astonishing level of the diversity of prokaryotes. Their diversity is what allows them to prosper and survive in practically any environment from ice to boiling water. Their diversity occurs from many successful mutations, and changes in their genetic structure. Whitman calculated that prokaryotes produce 17.4x1029 cells every year, which leaves them with a number of chances to develop helpful mutations. They decided that four changes in a single gene were an indication that a prokaryote might have changed enough to form a new enzyme and thus begin differentiating itself from its ancestors. These mutations are said to take place on Earth every 20 minutes (Eberhard, 1990).

Bacteria perform a number of jobs because of their diversity. Decomposing, sometimes called mineralization, is one of the most important jobs that bacteria do (Campbell et al.). Bacteria decompose dead organisms and release essential nutrients into the air and soil. Another important job of bacteria is nitrogen fixation, or nitrogen cycling. Several groups of bacteria metabolize nitrogen compounds unavailable to other organisms. Certain kinds of bacteria called rhizobium live in nodules on the roots of these plants by symbiosis. Rhizobium conduct the nitrogen cycling. What happens is that green plants can not use the nitrogen in the air, so nitrogen-fixing bacteria change the atmospheric nitrogen into simpler substances called nitrites (Wassneaar). By doing so, these prokaryotes play critical roles in the cycling of nitrogen in the environment. The ability or inability to survive in the presence of oxygen also reflects variation metabolism.

Bacteria are also important in medicine. When dead or weakened bacteria are used to prevent other bacteria diseases, it is called vaccination. Bacteria can also be used to help make drugs, hormones, or antibodies. Lately, scientists have found bacteria helpful in the break down of oil and to assist in oil spill clean ups.

Finally, bacteria are used extensively in the commercial industry. Dr. T. M. Wassenaar tells us that they help in “tanning, making linen, curing tea and tobacco leaves, extracting precious metals from rock, coloring foods, coloring cosmetics, tenderizing meat, removing stains, processing paper, processing cloth, changing one chemical into another, and much more.”

As there are positive aspects to bacteria, there are also negative aspects that can be harmful. Bacteria have devised a number of strategies to cause illnesses. These strategies are called bacterial pathogenicity. Bacteria need to be able to stay in close contact to our body and to multiply there before they can cause us any harm. The only exception to this rule is in the case of food poisoning. Pathogenic bacteria have certain characteristics that they need in order to cause disease. These are called virulence factors and have specific functions in the steps that ultimately result in an infection. David Tenenbaum describes an infection as “a miniature battle between bacteria and host, the first trying to remain present, and to feed and multiply, while the host is trying to prevent this.” In the end there are three possible outcomes, the host wins and the bacteria are removed (possibly with the help of medicine), the bacteria win and kill their host, or an equilibrium is reached where the host and bacteria live involuntarily together and damage is minimized. Some examples of virulence factors produced by bacteria are fimbria, or pili. These are hair-like structures on the surface of the bacterial body. These hairs attach to certain sites of our body and so the bacteria can not be washed away. E. Coli is one example that produces fimbria to attach to the epithelium lining of the urogenital tract.

Another factor is with flagella. Flagella are long tails that help the bacteria swim. The motion helps the bacteria reach the site where they can survive. Some bacteria produce toxic compounds to cause harm to their host. These factors are called toxins. Toxins can induce vomiting, diarrhea, can paralyze nerve cells, cause muscular cramps, severe pain, and fever. In some cases bacteria produce toxins wherever they grow, and if we happen to eat those bacterial products we get sick, even without being infected by any living bacteria. That is what happens in many cases with food poisoning. The last factor is called invasion. Some bacteria have learned to invade our cells. Some bacteria will destroy the cells of our intestine to feed and the result is severe diarrhea. One type of bacteria, Mycobacterium tuberculosis, enters our bodies through the lungs and will remain there feeding off the nutrients in the cells because our immune systems are not capable of destroying these hidden cells (Campbell et al.).

Bacteria can harm humans by causing a number of diseases that can ultimately end in death. There are different types of bacteria and each one affects humans differently, some are worse than others. The bacteria streptococcus is divided in two groups, Group A and Group B. Group A streptococcus is not as bad as Group B. In Group A streptococcus there are approximately 3.2 cases per 100,000; estimated 9,000 cases. Of those, 1,000 result in deaths annually in the United States. Group B on the other hand results in 6.9 cases per 100,000; estimated 18,900 cases and has approximately 1,900 deaths annually. Another bacteria, Haemophilus influenzae, affects humans every year. This bacteria results in 1.3 cases per 100,000; estimated 3,400 cases and 625 deaths annually. The bacteria Neisseria Meningitidis has .8 cases per 100,000; estimated at 2,200 cases and 275 deaths annually in the United States. The bacteria streptococcus pneumoniae has 21.9 cases per 100,000; estimated at 60,000 cases and 6,700 deaths annually. This bacteria affects humans much more than any of the other bacteria previously mentioned. Another very popular bacteria that results in 79,420 cases each year in the United States is Enterotoxigenic E. Coli. This is the most common cause of travelers’ diarrhea and has caused several food-borne outbreaks in the United States. There is a bacterium that affects even more people than Enterotoxigenic E. Coli does. That bacterium is Enterobacteriaceae of the genus Salmonella. There is an estimated 1.4 million cases annually in the United States (Centers for Disease Control and Prevention, 2002).

Disinfectants and biocides are a chemically diverse group of agents which are generally considered to exhibit poor selective toxicity. All anti-bacterial agents operate using one of three types of action: physical, chemical, or ionic. Regardless of the type of action used the objective is the same: the destruction of bacteria. Disinfectants go about this in several ways. One type is through disruption of the transmembrane motive force by preventing the accumulation of transmembrane force. This type of biocide prevents the cell from carrying any material in to or out of the cell (Birch, 1997).

Another method is inhibition of respiration or anabolic rations. This method prevents the cell from carrying out chemical processes necessary for bringing oxygen into the cell and carbon dioxide out, or vice versa. This method also prevents the cell from bringing in food and energy products. Disruption of replication is another type of method that is often used in conjunction with other methods. However, it can be quite effective on its own. By preventing the cell from dividing or replicating, you can assure that the generation being exposed to the agent will be the last generation of that organism in a given sample. In the method of loss of membrane integrity/cellular leakage, the membrane is decomposed. Chemical agents can effectively destroy a cell. Breaching the cellular membrane allows the intracellular constituents to leak out, and it allows foreign materials to enter the cell. This is one of the most common methods of bacterial destruction, however, because of the membrane that occurs; bacterial DNA is often left behind. This can pose a serious threat and lead to bacterial resistance to antibiotics.

The process of lysis is one of the most effective in the disinfectant arsenal; however it is also one of the slowest acting. Lysis causes a dis-coagulation of the material inside the cell without breaching the cell membrane. This kills the organism and prevents the DNA from becoming exposed. Coagulation of intracellular material is the opposite process of lysis. Just as lysis causes a thinning of intracellular fluids and structures, coagulation results in the opposite effect. The fluids within the cell become semi-solid in nature and prevent any of the natural processes from occurring and thus destroy the cell. In the most extreme cases of coagulation, the cell hardens to such a point that it solidifies in a state of seeming biostasis with all of the structures imprisoned within the cell. Although we have ways and methods to kill bacteria, they can multiply in 30 minutes or less. So even if you would wipe out 95% of all bacteria in your kitchen, it would take less than three hours to get them back, provided that they had enough to feed on.

The strain of bacteria we believe to be working with is Staphylococcus epidermidis. The genus staphylococcus was discovered and named by Ogston in 1881 when he observed grape-like clusters in human abscesses. Staphylococci are perfectly spherical, and are about one micrometer in diameter. Because this bacterium divides in two planes, they grow in clusters, which helps define them from a similar type of bacteria, Streptococcus (Jones, 2001).

Staphylococcus is mainly feared in post-operative infections. It is the most common bacteria associated with human infection these days. This type of Staphylococcus is generally found on human skin. This is why it is a good bacterium to perform this experiment on. Our hands touch thousands of objects each day all over our house, workplace, and other public places, giving bacteria thousands of opportunities to infect us. Using disinfectants regularly will help reduce this risk of becoming ill (Todar, 2001).

 

Relevance of Research

Other researchers and researching organizations, such as the Consumer Reports have performed similar experiments. The conclusion that they arrived at was that it was not worth paying the extra money to purchase a potentially more powerful disinfectant because it is impossible to sterilize every surface in your home, and sterilize the air. Bacteria are still present in the house, and will only come back after careful sterilization. They suggest that consumers purchase the cheaper all-purpose cleaners instead of the more expensive name brand cleaners that specifically attack certain areas of the house or the bathroom (Consumer Reports, 1991).

This project will contribute to the broader base of human knowledge by making the consumer more aware. By completing and analyzing our experiment and results, we will better educate the public on which brands are effective and which ones are not. It will also help consumers make more educated decisions on selecting anti-bacterial brands.

Along with our experiment, we conducted a survey about how the four different brands of disinfectant are perceived by college students (Attachment 1). In the survey we asked them to rate each brand on a scale from 1-6 on how effective they thought it would be in killing bacteria. We then asked them which brand they felt was the most effective, and which one was the least effective based only on their perceptions of the product from any media that they have seen about the product or the store that produced it. This survey is relevant to our research because of our concern about the consumer. We want to look at how the image of each product actually portrays itself in the eyes of the public. It will also be interesting to see which brand the public chooses as the best, and compare that with which brand actually kills the most bacteria.

 


Materials and Methods

The materials for culturing bacteria were obtained from the Microbiology department at Miami University, and the anti-bacterial agents were purchased at local convenience stores. To begin with, the bacteria needed a medium in which to grow. We used 10 Petri dishes that contained a medium of Agar, which served as food for the bacteria to grow on. In order to obtain the bacteria from the environment for culturing, we used sterilized swabs to collect bacteria samples. To grow the bacteria once it is collected, we acquired an incubator to keep the bacteria in a controlled environment to ensure optimal growth. To apply the antibacterial agents to the bacterial contaminated Petri dishes, we used filter papers. The filter papers were soaked with antibacterial solutions and then applied to the Petri dishes. In order to test the effectiveness of the anti-bacterial agents, the bacteria first needed to be collected and cultured. We collected the bacteria using the sterile swabs to swab the inside door handles of the front door of Peabody Hall, a Miami University dormitory. The contaminated swabs then were smeared onto a Petri dish containing Agar. The contaminated Petri dish then was set in the incubator for approximately 24 hours. Since there are countless bacteria in the environment, the sample was no doubt a lawn of many different types of bacterium. We randomly swabbed a colony of bacteria from the original Petri dish, and smeared it onto 16 new Petri dishes.

Onto the second set of Petri dishes, which were cultured from one bacteria colony of the original Petri dish, we added the antibacterial agents. We soaked the filter papers in each anti-bacterial agent. Three soaked filter papers were placed onto each of the dishes from the second set. Each dish contained six filter papers of an anti-bacterial agent, and a control un-soaked filter paper, a total of seven filter papers (Figure 1). This second set of dishes was incubated for a period of 24 hours. After this time, the dishes were observed, and the diameters of the areas where no bacteria grew were measured, and the areas of these auras were calculated. Four complete trials were done, and four sets of data were collected in order to compare the different anti-bacterial agents.

 

Figure 1. Petri dishes from the second set with filter papers and
visible auras.

To try and discern which agent is the more affective anti-bacterial agent, we compared the surface areas of the auras around the filter papers. This told us which brand is more effective in hindering the growth of bacteria. These results were then compared in StatView and SuperANOVA, statistic analysis computer programs, in order to more accurately determine if there were significant differences in the effectiveness of the agents.

In an attempt to measure public understanding of the relative effectiveness of anti-bacterial agents, one hundred surveys were distributed (Attachment 1). The completed surveys were collected and analyzed.

 

Timeline

10.17 Obtain materials
10.22 Collect bacteria samples
10.22~10.24 Culture bacteria (original)
Week 1
10.24 Swab one bacteria colony (primary colony) of the original culture onto a plate, and apply anti-bacterial agents
10.24~10.29 Observation and data collection
Week 2
10.31 Swab the primary bacteria colony from the original culture onto a plate, and apply anti-bacterial agents
10.31~11.05 Observation and data collection
Week 3~5 (Repeat Week 2 procedures)
11.24 Statistical Analysis

 

Results

The data sets of aural size were collected by measuring four different diameters of the auras at different angles, 0° (D1), 45°(D2), 90°(D3) and 135°(D4) (Data Sheet 1-4). The average diameter of the four diameters was then determined in the calculation of the aura area. Applying the area formula for circles, the aura areas, including the inner dots were calculated. This whole area was then subtracted by the area of the dot to find the true area of the auras, which are shown in the Data Sheets.

DATA SHEET 1

DATA SHEET 2

DATA SHEET 3

DATA SHEET 4

(all data sheets are posted as excel files)

Average diameters of the auras –
daverage = (d1 + d2 + d3 + d4) / 4
Examples –

Wal-Mart Set 1/ Dot 1/ First Time
dD1average -= (1.35cm + 1.40cm + 1.35cm + 1.35cm) / 4
= 1.3625cm

Lysol Set 2/ Dot 2/ First Time
dD2average = (1.95cm + 1.95cm + 1.95cm + 1.97cm) / 4
= 1.955cm

Clorox Set 3/ Dot 3/ First Time
dD3average = (2.50cm + 2.50cm + 2.50cm + 2.51cm) / 4
= 2.5025cm

Kroger Set 4/ Dot 4/ First Time
dD4average = (1.70cm + 1.71cm + 1.72cm + 1.71cm) / 4
= 1.71cm

Surface areas of the whole auras (with dot) –
A = πr2
Examples –

Wal-Mart Set 1/ Dot 1/ First Time
AD1 = π(1.3625cm/2)2
= 1.4580cm2

Lysol Set 2/ Dot 2/ First Time
AD2 = π(1.955cm/2)2
= 3.0018cm2

Clorox Set 3/ Dot 3/ First Time
AD3 = π(2.5025cm/2)2
= 4.9186cm2

Kroger Set 4/ Dot 4/ First Time
AD4 = π(1.71cm/2)2
= 2.2966cm2

Area of Dot –
AD = πr2
AD = π(1/2)2
= 0.7854cm2

Area of Auras (without dot) –
Afinal = A – AD
Examples –

Wal-Mart Set 1/ Dot 1/ First Time
Af = 1.4580cm2 – 0.7854cm2
= 0.6726cm2

Lysol Set 2/ Dot 2/ First Time
Af = 3.0018cm2 – 0.7854cm2
= 2.2164cm2

Clorox Set 3/ Dot 3/ First Time
Af = 4.9186cm2 – 0.7854cm2
= 4.1332cm2

Kroger Set 4/ Dot 4/ First Time
Af = 2.2966cm2 – 0.7854cm2
= 1.5112cm2

 

To compare the effects of the four different types of disinfectants, standard deviations were calculated from the means and the distribution of the data sets. In Figure 1, this standard deviation is graphed, where we can see a clear distinction of the Clorox disinfectant from the rest. Statistical analysis was also performed, where the P-value was found (Table 1).

Table 1. The effects of disinfectants on aural area

 

Further analysis was done with the Scheffe’s significance test (Table 2). In this test, the four different disinfectants were broken down and compared. P-values were found to determine if there was a statistically significant difference between the results yielded by the disinfectants being compared

 

Table 2. Scheffe’s: The differences between disinfectants

Statistical analysis was also done to determine the effect of time on the aura area. The data sets from the first day and the third day were compared and the P-value was calculated to be 0.5554 (Table 3).

 

Table 3. The effects of time on aura area.

 

With the effects of disinfectants and time investigated separately, we combined the two variables and also calculated a P-value to determine the effects of both on the aura area (Table 4). The difference can be clearly seen in Figure 2 between Clorox disinfectants and other brands, however, there are no clear distinctions between the two days when the data were collected.

 

Table 4. The effects of disinfectant and time on aura area.

 

 

Table 5. The effects of time on aural diameter.

 

 

At the beginning of the experiment, we surveyed 100 Miami University students about the their perceptions and experiences with the four different brands of anti-bacterial agents. After we collected the surveys, we tallied the responses and performed basic statistical analysis on them. Figure 5 shows the population’s perception on which of the four brands is the most effective anti-bacterial agent, and figure 6 shows the population’s perception on which is the least effective brand.

 

Figure 5. Which brand is the most effective anti-bacterial agent?

 

Figure 6. Which brand is the least effective anti-bacterial agent.

 

Figure 7. Comparison of aura size of different brands of anti-bacterial agents. (Clockwise from top left: Clorox, Kroger, Lysol, Wal-Mart.)

 

 

Discussion
When we began this experiment, we expected to find that the name brands would be significantly more effective against the bacterium than the generic brands. Our results showed that the Lysol, Wal-mart, and Kroger brands were all comparable in their effectiveness, while Clorox was much more effective than any of the other brands (Figure 2). These findings contradicted what we had originally thought, and led us to believe that there was something more than brand names that make the difference. So in regards to our hypothesis, the results of the experiment showed that of the brands that were tested, it was not the brand name that made a difference in the effectiveness of the antibacterial agent. These differences could be attributed to a number of factors that will be emphasized in the following discussion.

The Kroger store brand antibacterial was shown to have a level of effectiveness similar to Lysol and Wal-Mart brands. All three share a common active ingredient, ammonium chloride. The Kroger brand was able to hold back the bacteria at an average aural diameter of 1.841cm (Data Sheet). There was no notable decline in the strength of the agent during the three-day observation period. When compared to the more expensive name brand Lysol product, no difference in performance could be observed, as the P-value of .8145 suggested (Table 2).

The Wal-mart brand disinfectant that we used in the experiment showed similar results to that of the Lysol and the Kroger brands. When the diameter of the Wal-mart brand was compared with those of the other generic brand, Kroger brand, the comparisons showed that there was no significant difference in the diameters that were measured from our trials (Figure 7). This showed that the generic brands had similar effectiveness in killing bacteria. Similarly, when the diameter values were converted to surface areas in order to see how much area the antibacterial were affective in killing the bacteria, and ran through statistical analysis, the results also turned out with a P-value of greater than .05, which shows no significant difference in the effectiveness of the two brands (Table 2). When the diameter and the surface area values produced by the Wal-mart brand was compared to that of Lysol also yielded a P-value of grater than .05, which shows no significant differences between the two (Table 2). Since the active ingredients of these two antibacterial agents are the same, it is possible that the only difference truly lies with the label. When compared to the name brand Clorox, however, our predictions did hold true. When the diameters of the auras of the Wal-mart brand was compared to that of Clorox, the P-value showed a significant difference between the results (Table 2).

Some startling results were found when the four Wal-mart trials were compared to each other. The first plate showed significant differences as compared to the rest of the trials (Figure 4). This could have been due to the amount of antibacterial that was sprayed on the filter paper. It is possible that the filter paper was more saturated with the antibacterial for the later trials than in the first. The amount of bacteria smeared on the plate could have also played a role. If there was a more concentrated culture of bacteria on the first plate as compared to the later ones, the results yielded could have been affected. Either one of these explanations could account for the first plate of the Wal-mart brand showing a significantly lower effectiveness than the rest of the plates.

The name brand antibacterial, Lysol, that we used in this experiment, was shown have comparable effectiveness to that of the generic brands. When comparing the average diameters of the auras of Lysol to the generic Wal-mart and Kroger brands, the P-values were all much greater than .05, showing that there is no significant difference in the performance of these products (Table 2). Likewise, when the results were converted to the area of effectiveness of the antibacterial agents, the results showed no significant difference. This can be attributed to the ingredients of all three of these brands. The active ingredient of these brands is all the same, and the only differences were in the price of Lysol, which was close to double the price of the generic brands. When Lysol was compared to Clorox, however, the results were much more dramatic. The measures of the auras of Lysol, when compared to Clorox, had a P-value of .0001, which shows a significant difference in the data collected (Table 2). This result was contrary to our original hypothesis. The reasons for this could be due to the active ingredients of Clorox, which is the only agent to have octyl decyl dimethyl ammonium chloride as the leading active ingredient.

The most effective anti-bacterial agent tested in our experiment was the Clorox based chemical. With an average aural diameter of 2.539cm (Data Sheet), Clorox had an aural diameter of 0.698cm larger than Lysol, the next best performer. Clorox was the only anti-bacterial tested to use octyl decyl dimethyl ammonium chloride, as its active ingredient. When compared to the other agents tested, the difference between Clorox and any other is both significant and notable. When Clorox was statistically compared to the Wal-Mart brand, the P-value was less than .0001 (Table 2). Similarly, when Clorox was compared to Kroger brand the P-value was less than .0001 (Table 2). Finally, when Clorox and Lysol are compared, the P-value was also less than .0001 (Table 2), all showed that there was a significant difference in the effectiveness of Clorox from the other three brands tested. With the help of this data, we concluded that Clorox is the most effective anti-bacterial tested having an average aural radius that is 73% larger than the closes competitor.

With regards to the bacterial resistance, we decided to take one of our plates to the Microbiology department for an analysis of the bacteria to try and find out what kind of bacteria we were dealing with. Microbiologists at the department informed us that it was impossible to obtain an exact bacterium without extensive testing, but they were able to narrow it down to Staphylococcus, which is a Gram-positive bacterium responsible for many common illnesses (Todar, 2001). K. Todar also mentioned that this particular bacterium can only take up to 15% NaCl in its environment. When looking at the ingredients of the antibacterial agents, Clorox has a different active ingredient that includes a chloride. For this reason, it is possible that the Clorox solution is found to be more potent against this particular bacterium because of its active ingredient, but may be less affective against another kind of bacteria that the Lysol, Kroger, and Wal-mart brands might be more affective. It is also a possibility that the cleaners use Lysol to clean the banister that we swabbed for our bacteria, and that the bacteria had gained a resistance to that antibacterial agent, altering the precision of our experiment.

As with all biological processes, time plays an important role. Our experiment called for two sets of measurements to be taken. The first sets of data were taken 24 hours after each plate was activated, and then again 72 hours after activation. In this short duration, there was no significant decline in the effectiveness of any of the anti-bacterial agents (Figure 3).
As is often the case, the understanding of the general pubic is at odds with the results of scientific analysis. In a survey of 100 Miami University Students (Attachment 1), 68% believed that Lysol would be the most effective in combating bacteria (Figure 5). Our study proved otherwise. Only 12% of students hold that the Clorox based disinfect will be the most effective and 11% thought the Wal-Mart brand would be the most effective, while only 9% chose Kroger (Figure 5). The Kroger, Wal-Mart and Lysol products were approximately equal in their effectiveness at combating bacteria with an average aural radius of 1.798 cm between them. However their retail prices do not coincide with performance. Both Wal- Mart and Kroger sell for approximately $2.15 per bottle, while the equally effective Lysol holds a price tag of $3.25, and increase of 66% in price for a negligible difference in effectiveness. Clorox priced at $3.95 per bottle did show an improvement in effectiveness. The aural radius observed on the Clorox treated plates was 60% larger that those observed on any of the other plates. It is the opinion of this research team that poor marketing and advertising is to blame for the lack of consistency between actual product effusiveness and the product’s effectiveness as perceived by the customer.

Future research projects can attempt to further this research. For example, an experiment conducted over many weeks could explore the role of time in the effectiveness of anti-bacterial agents. The role of viscosity can also be explored. Thicker chemicals may produce initially smaller aural rings, but they may be effective for longer periods of time. Finally, future experiments can also involve the use of dilutions. The comparative effectiveness of some agents at a non-full strength could prove both interesting and productive.

 

 

 

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Riley, Margaret A and Michael Felgarden. 1998. High Levels of Colicin Resistance in Escherichia coli. Evolution. 52 (5): 1270-1276.


Tenenbaum, David. 1998. Microbial Population Explosion. University of Wisconsin Board of Regents.


Wassenaar, Dr. T.M.. 2002. The Museum of Bacteria.

 

 

ATTACHMENT 1