The effects of disinfectants and antibacterial soap on bacterial growth

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The effects of disinfectants and antibacterial soap on bacterial growth

Abstract
The effects of various disinfectants and one brand of antibacterial soap on bacterial growth were examined. Different cleaners containing either ethanol, sodium hypochlorite, or triclosan as a primary ingredient were added to culture tubes containing bouillon broth and bacteria taken from the classroom. Bacteria from each tube were regrown on agar plates to determine whether the disinfectant or soap, which had been added to the bacteria's rood source. was effective. Under the conditions of the experiment, all cleaners tested proved satisfactory in killing the bacteria found in the classroom.

Introduction.
Hospitals are supposed to be clean, right? All bacteria living on countertops and on other surfaces arc supposed to be killed with routine applications of potent cleaners to provide a sanitary environment for patients. But would it be possible for the disinfectants used in hospitals to be less effective than the manufacturing companies claim'? Our doubts were raised by a previous experiment that had been performed on different brands of soap, which had indicated that not all soaps were as effoctive as they claimed [1].

Clearly, our question was a pertinent one. At the very least, the patients and doctors might be concerned if going to the hospital meant being exposed to a whole range of bacteria and other microorganisms. Therefore, we rummaged through the cabinets in the Urgent Care Center at Palo Alto Medical Foundation, and collected samples in sterile urine cups of cleaners used in the clinic.- specifically, we retrieved samples of Coverage Spray, Lysol, Enviroquat, and Envirocide. Lysol was supposed to be effective for only "household germs and bacteria on environmental surfaces," but the other cleaners all claimed to kill at least Staphylococcux aureus (found on human skin), and Salmonella typhosa or Salmonella choleraesuis. Many were supposed to be virucidal, tuberculocidal, fungicidal, and pscudomonacidal. To compare between disinfectant sprays and antibacterial soap, we also collected a sample of Bacti-Stat, the single antibacterial soap used in the clinic by doctors. Finally, Clorox Bleach, commonly used to kill bacteria, was tested.

Because hospital bacteria can be dangerous, bacteria was taken from the classroom instead and grown in broth. A single substance (disinfectant, soap, or deionized water) was added to various culture tubes containing broth and bacteria. One day later, sterile agar plates were inoculated with bacteria from each tube and incubated. Growth was examined first on the following day, and once again three days later. We hypothesized that not all cleaners would prove effcctivc, simply because of the precedent sent by the aforementioned experiment performed on antibacterial soaps.

Materials and Method.
Two sterile agar plates were inoculated with bacteria taken from a classroom doorknob, from our hands, and from an unusually dirty spot on a desk. For one day, the plates were incubated at 37' C to encourage growth-, (he bacteria present by the next day were transferred aseptically to an Erlenmcycr flask containing 75 mt, of sterile beef bouillon broth, The broth was made using 200 mL tap water per beef bouillon cube. Thc flask was incubated at 37' C for another clay, and the contents were agitated on a frequent basis except for during the period of time between approximately 3:00 PM and 10:45 AM the following morning.

The broth and bacteria mixture was agitated, then, using aseptic technique and a disposable sterile pipet, 2 mL of broth and bacteria mixture were quickly pipetted into each of seven sterile culture tubes. 10% Clorox Bleach was mixed. 2 mL of each cleaner were added to the first six tubes, making a 1: 1 ratio of cleaner to broth and bacteria mixture. All disinfectants were working at half their standard concentrations-, we were curious to see if they would still be effective. 2 mL of deionized water were added to a seventh tube containing broth and bacteria: this tube served as control #1, which would indicate whether or not bacteria was present in the broth and bacteria mixture being tested. Finally, as a second control, sterile broth that had not been inoculated was added to an eighth sterile culture tube. (See Appendix A for summary of contents tubes.)

The eight tubes were placed on a rack and left at room temperature overnight. Thus, the cleaners were given twenty-four hours to take effect, and then the bacteria from each tube was regrown on agar plates. Eight bleached glass pipets were used to aseptically pipet 0.3 mL from each culture tube on to eight sterile agar plates, which were then tilted from side to side to spread the bacteria, broth, and cleaner mixture evenly over the agar surface. Standard amounts were pipetted to ensure that each plate would have basically the same amount of bacteria added to it. The plates were labeled and incubated at 32' C (because 37' C had melted the agar on two out of three of our previous plates). Observations were made one day later. We were uncertain about the presence of bacteria on some plates. Bacti-Stat was so thick that it formed an opaque layer on the agar and obscured any potential bacterial growth-, the Lysol, Enviroquat. and Coverage Spray plates had specks that could have been either bubbles or colonies of bacteria whose growth was inhibited by presence of the disinfectant. Therefore, we divided another sterile agar plate in fourths and inoculated from the plates in question to see if bacteria would grow on the new plate.

Results.
Observations taken on first day (see Appendix A for summary):

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The first observations taken showed growth only on the first control, which was broth and bacteria with water added. Control #1 featured puntiform and circular colonies across the entire agar surface. Neither the Clorox nor the Envirocide plate had visible colonies. Bacti-Stat had an opaque layer that covered the agar surface, so we could not determine whether or not growth had occurred. Coverage, Lysol, and Enviroquat did not appear to have growth, but upon further examination, we noticed tiny specks in all three plates that could have been either bubbles or potential colonies. Because the presence of too much disinfectant ...

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***** A very detailed account of an investigation in which it is difficult to control variables. A good understanding of sources of error shown in the discussion.