Lab: the Bacteria Around You

Lab: The Bacteria Around You James Brunet Ms Owen October 14th, 2012 Part 1 Purpose To culture and observe the various types of bacteria found around Canterbury High School. Materials and Methods Refer to pages 422-425 of Biology 11 McGraw-Hill Ryerson and the handout “Gram Staining Procedure”. Observations Table 1: Locations of Bacteria Samples Quadrant| Location of Sample Obtained| 1| Floor| 2| Water fountain head| 3| Auditorium Chair| 4| Inside of Boys’ Bathroom Door Handle|
Table 2: Growth of Bacteria from Various Locations Around CHS after 48h in Incubator Quadrant| Total Number of Colonies| Description of Colonies| Number of Colonies| 1| 1| Irregular, flat, and lobate. Occupies entire quadrant. | 1 | 2| About 8| Milky-white coloured, punctiform, and entire. | 6| | | Milky-white coloured, punctiform, and curled. | 2| 3| 10| Milky, punctiform, and entire. | 8| | | Yellow, punctiform, and entire. | 2| 4| 8| Milky, irregular, lobate, and raised. | 1| | | Milky, punctiform, and entire. | 4| | Milky, punctiform, and curled. | 2| | | Clear, flat, circular, and undulate. | 1| Discussion What areas around the school appeared to have the most bacteria? The least? Suggest reasons for these findings. The area around the school that appeared to have the most bacteria was the inside of the boy’s bathroom door handle. Not only did it have the most diverse range of bacteria (four different types), it also had the 2nd highest number of colonies! The area around the school with the least bacteria was, in my opinion, the floor.
Although the single colony there grew very large, this was probably due to lack of competition, as there were no other colonies present. This seems to indicate that there is actually less diversity of bacteria on the floor than on a door handle. I think that the door handle appears to have more bacteria for two main reasons. Firstly, the door handle is gripped by students exiting the bathroom. Some of these students may not have washed their hands, leading to bacteria being transferred from person to handle constantly. Secondly, these handles are rarely, if ever cleaned, while the floors are cleaned on a daily basis.

Describe the conditions necessary for bacterial growth. Bacteria need food, moisture, warmth, and time to grow. The agar plate provides the food and some moisture, the incubator provides growth, and if it is an expensive unit, moisture as well, and you as the student provides the time. Describe two factors that may limit bacterial growth. A lack of moisture may limit bacterial growth. Instead of multiplying, the bacteria may die. As well, a less than optimal temperature may limit, and perhaps completely stop, bacterial growth.
Temperatures outside of the range of 4°C-60°C (The bacterial “danger zone”) will stop most bacterial reproduction and kill many species of bacteria. However, some bacteria can survive with very little moisture for extended periods of time and thrive outside these temperature ranges. Did this experiment have a control? If not, suggest what control you could set up and why? This experiment did not have a control. If I was to set up a control for this experiment, I would leave one of the quadrants clear of any specimen, and use it as a control quadrant.
If I did that, I could tell if bacteria was already present in the agar if the control quadrant grew colonies. Discuss some aspect relating to your samples or the procedure. I would like to retest the floor sample, because the single colony left me thinking that the data was incomplete. I just don’t think there is only one type of bacteria living on the floor. I think I would like to change the procedure, as a control quadrant is vital to the integrity of the experiment! As well, I am definitely not going to open the boy’s bathroom door and then proceed to touch my eyes immediately after. Conclusion
In conclusion, the bacteria from the floor, water fountain, chair, and door handle flourished because of the warmth of the incubator, the food/moisture present in the agar, and the time we gave it. We identified multiple colonies of bacteria by their colours, sizes, shapes, and thicknesses, and also by staining them with Crystal Violet and Safranin. All of these things combined gave our group insight into the conditions necessary for bacterial growth, how to identify colonies, and where bacteria grow most. Part 2 Purpose To test the effectiveness of various disinfectants and antibiotics on limiting bacterial growth.
Materials and Methods Refer to pages 428-429 of Biology 11 McGraw-Hill Ryerson. Observations Quadrant| Type of antibiotic/disinfectant| Size of zone of inhibition| 1| Soap| Huge zone-extends into quadrant 3. | 2| Organic disinfectant| Midsize zone| 3| Bleach+Comet| None| 4| Hand sanitizer| None| Discussion How was the effectiveness of each antibiotic/disinfectant measured? The effectiveness of each antibiotic/disinfectant was measured by looking at the zone of inhibition, the size of the area immediately surrounding the antibiotic that is colony-free.
Which inhibitor was the most effective? Explain. The soap was by far the most effective inhibitor. Its zone of inhibition extended so far that it even reached into a neighbouring quadrant! This means that the soap was extremely effective at stopping bacterial growth. Rank the inhibitors you used by their effectiveness. Explain your reasoning. I found soap to be the most effective inhibitor, and the organic disinfectant to be the second most effective inhibitor, with respect to their zones of inhibition.
I ranked hand sanitizer and bleach+comet as a tie for last place, because they did literally nothing to stop the growth of bacteria. I ranked these inhibitors in this order because I believe that effectiveness can easily be measured by the size of the zone of inhibition. Why is it important for a physician to know the exact identity of the bacteria involved in an infection? It is important for a physician to know the exact identity of the bacteria involved in an infection because different inhibitors work for different bacteria.
If the physician incorrectly identified the bacteria, his prescribed antibiotics may do nothing against the bacterial infection, and the patient’s sickness would actually worsen. This is easily shown by our zone of inhibition experiment, where of the four chosen antibiotics, two of them did absolutely nothing against the bacteria. Conclusion In conclusion, it is important to know how to both identify bacteria using morphological clues as well as it is important to know how to treat said bacteria. Not all bacteria are the same, and not all antibiotics are on the same footing either.

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