Effects of household cleaners on Escherichia coli
Brian Agee
Department of Biology
Tennessee Technological University
Cookeville, TN38505
Abstract
The purpose of performing this study was to determine if Escherichia coli was susceptible to common household cleaning agents and to determine which cleaning agent is the most effective at killing the bacteria by acting as a bactericidal agent. Six common household cleaners (Clorox bleach, Ajax dishwashing liquid, 409, vinegar, Germ-X, and Lysol) were tested against Escherichia coli in two assays. The first assay performed was a disc diffusion assay, which tested the cleaning agents’ ability of effectively inhibiting the bacteria. Results from this assay showed that all of the chemicals tested successfully inhibited the bacteria; however, it was observed that Clorox bleach was the most effective inhibitor of the bacteria, inhibiting the Escherichia coli three to four times greater than the other cleaning agents that were tested. The second assay performed was a tube growth assay, which tested each cleaning agents’ ability to kill the bacteria. The results from this test showed that all of the cleaners used were able to effectively kill Escherichia coli, even when the cleaning agents’ concentration was reduced to fifty percent. Escherichia coli was shown to be susceptible to all of the household cleaners that were tested in this particular study; however, Clorox bleach was by far the most effective cleaning agent used to inhibit and kill the bacteria.
Key Words
Escherichia coli, disinfectants, effectiveness, susceptibility, household
Introduction
Escherichia coli is a common bacterium that usually lives in the intestines of people and animals. According to the Centers for Disease Control, Escherichia coli is a leading cause for food-borne illnesses and is estimated to cause 73,000 cases of infection and 61 deaths every year (CDC 2006). “The cost of food-borne disease in the USA has been estimated at $4-$6 billion” (Rusin 1998). Most strains of Escherichia coli are harmless; however, a strain called Escherichia coli O157:H7 produces a very powerful toxin that may result inhemorrhagic colitis and thehemolytic uremic syndrome (Besser 1993).
“An increase in food-borne illnesses has been observed in many countries recently, with a high proportion of these outbreaks occurring in the home” (Rusin 1998). The most notable area where bacteria were found was in the kitchen, where, especially in the kitchen sink, large numbers of Escherichia coli was found (Josephson 1997). As pointed out in a study performed by Cogan, the main cause of this food-borne infection is considered to be inadequate cooking and storage of food, but also includes poor hand and surface hygiene (Cogan 2002).
Recent outbreaks of Escherichia coli have brought the issues of hygiene and disinfection to the public (Cogan 2002). Because of this public attention, antibacterial agents marketed for the home have increased from only a few dozen in the mid-1990s to more than 700 today. Now, the public is being bombarded with advertisements for cleaners, soaps, detergents, and hand lotions that all contain antibacterial agents (Levy 2001). According to Kusumaningrum, in order to determine the efficiency of antibacterial products, their use in a household setting must be considered (Kusumaningrum 2002). In a study conducted by Cole, samples were collected from the homes of antibacterial product users and nonusers for the isolation of target bacteria. “Of 1238 isolates, more target bacteria were recovered from nonuser that user homes” (Cole 2003).
Sodium hypochlorite cleaners have been recognized for their disinfection properties for a long time. When used as part of a daily cleaning regimen, sodium hypochlorite can be effective at preventing infections by inhibiting and killing surface germs (Tsai 1999). Hypochlorite disinfection products used in combination with a regular cleaning schedule greatly reduces the amount of heterotrophic plate count bacteria and opportunistic pathogens that are commonly found in the household (Rusin 1998).
The objective of this study is to determine if Escherichia coli is susceptible to common household cleaning agents and also determine which cleaners are the most effective at inhibiting and killing the bacteria. I hypothesized that Escherichia coli would be susceptible to the cleaning agents and therefore will not be able to survive in their presence. This will lead to the rejection of the null hypothesis, which claims that Escherichia coli will not be susceptible to the cleaning agents and therefore be able to grow in their presence.
Methods and Materials
The procedure that was followed in order to carry out this study is similar to that of Dr. Susan Goss, which is found in her Health Sciences Microbiology Laboratory Manual (2005). For this study, a nonpathogenic strain of Escherichia coli was used to test the effectiveness of six common household cleaning agents. These cleaning agents included Clorox bleach, Ajax dishwashing liquid, vinegar, Germ-X, Lysol, and 409.
An Escherichia coli inoculum of 1.5x108 organisms/mL was made by comparing it with the McFarland Standard. To make the incoulum, Escherichia coli was swabbed and inserted into a broth medium. This procedure was repeated until the appearance of the Escherichia coli inoculum was as cloudy as the McFarland Standard solution. Once the inoculum was made, the actual experiment could begin.
The first experiment that was conducted is known as a disc diffusion assay and was performed by using the proper procedure (Goss 2005). This assay revealed if the cleaners are the most effective at inhibiting Escherichia coli based on the diameter of their zone of inhibition. In order to perform this assay, discs were soaked in individual cleaning agents and six TSA plates had Escherichia coli completely spread over them. Once the discs and plates had been prepared, each TSA plate was labeled according to which chemical they would be testing andthe disc containing the cleaner written on the plate was placed in the center of the plate. After all of the plates had a disc applied to them, they were all placed into the incubator and allowed to incubate for forty-eight hours.
The second experiment was used to determine which of the cleaning agents were the most effective at killing the bacteria. The procedure that was followed to perform this experiment was very similar to that of Dr. Goss (Goss 2005). To begin, test tubes were set up and labeled according to the cleaning agent that they were going to contain. Next, 1.0mL of nutrient broth was added to eight of the test tubes, six of which contained 1mL of the corresponding cleaning agent that was written on the test tube and the other two received no cleaner and was used as control standards. This procedure was repeated with the exception of using 2mL of the cleaning agents instead of 1mL. Once all of the tubes had been prepared, two drops of Escherichia coli inoculum was placed into each of the test tubes using a sterile pipette, and the test tubes were placed in the incubator for a period of forty-eight hours.
Once the forty-eight hour period had elapsed, the test tubes were removed and checked for growth. A cloudy appearance in the test tube was an indication that there was possibly the growth of an organism. In order to be certain, each of the broths were tested on TSA plates. Each TSA plate was divided into four sections and was labeled according to what was going to be streaked in that section from the corresponding test tube. To streak the plates, an inoculating loop was flamed in order to sterilize it, allowed to slightly cool for a second, dipped into one of the test tubes, and used to streak the section of the TSA plate that corresponds to what test tube you used (Goss 2005). After each of the test tubes had been streaked onto a TSA plate, the plates were placed in the incubator for a period of forty-eight hours. Any section on the plate that shows no growth after the forty-eight hour incubation period verifies that the cleaning agent used was effective in killing the Escherichia coli.
Results
The results of the disc diffusion assay are shown in Table 1. As seen in the table, it is clearly evident that Clorox bleach, with a zone of inhibition of 60mm, was the most effective at inhibiting Escherichia coli. The zone of inhibition of Clorox bleach was approximately three to four times larger than any of the other common household cleaning agents that were used in this study. Also, it is worth noting that Lysol and Ajax dishwashing liquid were also fairly effective at inhibiting this bacterium. Germ-X, vinegar, and 409 were effective at inhibiting Escherichia coli, but had notably smaller zones of inhibition than the other cleaning agents used in the study. As a whole, all of the cleaning agents that were used in the study were fairly effective at inhibiting Escherichia coli and produced an average zone of inhibition of 25mm.
Table 1: Zones of Inhibition for common household cleaning agents
Cleaning Agent / Zone of Inhibition (+ or -) / Size of Zone of Inhibition (mm)Clorox Bleach / + / 60
Germ-X / + / 13
Ajax / + / 25
409 / + / 15
Lysol / + / 20
Vinegar / + / 15
Average Zone of Inhibition for Common Household Cleaners / 25
The results from the tube growth assay, which was performed in order to determine if the cleaning agents were effective at killing Escherichia coli, is shown in Table 2. In this assay, as expected, the control tubes that contained only nutrient broth and Escherichia coli were the only test tubes that showed signs of cloudiness. Also, the control group was the only substance that produced positive growth on the TSA plates. All of the chemicals that were tested in this study proved to be effective at killing Escherichia coli even at reduced concentrations.
Table 2: Results from tube growth assay, which determined the effectiveness of the
cleaning agents at killing Escherichia coli
Cleaning Agent / Cloudiness in Test Tube (+ or -) / Growth on TSA Plate (+ or -)None (Broth+Bacteria) / + / +
Clorox Bleach / - / -
Clorox Bleach (50%) / - / -
Germ-X / - / -
Germ-X (50%) / - / -
Ajax / - / -
Ajax (50%) / - / -
409 / - / -
409 (50%) / - / -
Lysol / - / -
Lysol (50%) / - / -
Vinegar / - / -
Vinegar (50%) / - / -
A visual comparison of the zones of inhibitions of the various common household cleaning agents used in this study is shown below in Figure 1.
Figure 1: Zones of inhibition against Escherichia coli for common
household cleaning agents
Discussion
As pointed out in a study that was performed by Cogan, the main cause of the spreading of Escherichia coli is primarily the result of poor hand and surface hygiene (Cogan 2002). Today, the public attention on hygiene is at it highest point ever due to recent outbreaks around the world, with the majority of them occurring in the home (Rusin 1998). Because of this public attention, antibacterial agents that are marketed to the public have increased from just a few to several hundreds (Levy 2001).
From this study, consumers will be able to determine which of these cleaning agents work the best and will provide protection for themselves against Escherichia coli. In a previous study conducted by Tsai, it was discovered that sodium hypochlorite cleaners are effective at inhibiting and killing surface germs (Tsai 1999). Tsai’s work agrees with my findings because the hypochlorite cleaner Clorox bleach was discovered to be the most effective of all cleaning agents tested at inhibiting and killing Escherichia coli.
In a study that was conducted by Cole, samples were collected from homes of antibacterial product users and nonusers for the isolation of target bacteria, and he found that more target bacteria was recovered from the homes of nonusers than users (Cole 2003). The findings of Cole’s study also seem to agree with the results the tube growth assay that was performed in my study. The results of the tube growth assay showed that Escherichia coli could not grow in the presence of any of the cleaning agents that were used in this study; however, without the presence of the cleaning agents, Escherichia coli was able to grow. Thus, in order to reduce the risk of infections due to Escherichia coli, cleaning agents must be used on a routine basis.
Conclusions
As hypothesized, Escherichia coli was susceptible to the common household cleaning agents used in this study and was unable to survive in their presence. All of the chemicals that were tested were proven to be effective at inhibiting and killing Escherichia coli; however, Clorox bleach was found to be the best at killing and inhibiting this bacterium. Clorox bleach had a zone of inhibition of 60mm, which was three to four times greater than any of the other cleaning agents zones of inhibitions found in the disc diffusion assay. In conclusion, common household cleaners must be used in the household on a regular basis in order to help eliminate the chances of becoming infected by a bacterium, especiallyEscherichia coli. Furthermore, a hypochlorite cleaner such as Clorox bleach should be used to further reduce the chances of infection.
Acknowledgements
I would like to acknowledge the help of Dr. Susan Goss. Her assistance and use of the microbiology laboratory was greatly appreciated. Also, I would like to thank Dr. Morgan for his guidance throughout this semester.
Literature Cited
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[CDC] Centers for Disease Control and Prevention. 2005 Oct. 6. CDC homepage, Escherichia coli.< > Accessed 2005 Oct. 23.
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Appendix
Data Form(s)
Table 1: Zones of Inhibition for common household cleaning agents
Cleaning Agent / Zone of Inhibition (+ or -) / Size of Zone of Inhibition (mm)Average Zone of Inhibition for Common Household Cleaners
Table 2: Result from tube growth assay, which determined the effectiveness of the
cleaning agents at killing Escherichia coli
Cleaning Agent / Cloudiness in Test Tube (+ or -) / Growth on TSA Plate (+ or -)