Biology - Testing for Bacteria in Water

What are bacteria?

Bacteria are single-celled prokaryote micro-organisms. Prokaryotic cells are cells that have no nucleus in them. The diagram below shows a prokaryotic cell:

Bacteria can live in any habitat on Earth. They can grow in soil, acidic environments, hot springs, radioactive waste, water and deep in the Earth's crust as well as in organic matter and living bodies of plants and animals. In industry, bacteria are important in sewage treatment, the production of cheese and yogurt through fermentation, as well as biotechnology and the manufacture of antibiotics and other chemicals.

But how can bacteria be harmful to us?

There are approximately ten times as many bacterial cells in the human flora as there are human cells in the body, with a high number of bacteria on our skin. The vast majority of bacteria in our body are harmless due to the protective effects of the immune system and a few are even beneficial. However, there are a few species of this micro-organism that cause infectious diseases including cholera, syphilis, leprosy and bubonic plague. The most common fatal bacterial diseases are respiratory infections such as pneumonia, which kills about 2 million people per year. Even though bacterial infections are extremely dangerous, they are treatable by antibiotics.

Bacteria in seawater


Since the Ipanema beach and the Lagoa suffer pollution especially from sewage disposal, the water may contain some types of bacteria, with the most common one being E. Coli. As mentioned in the introduction to the project, studies have shown that prolonged contact with the waters from Ipanema beach and Lagoa can indeed cause various diseases including cholera, typhoid, dysentery, hepatitis and others.


Where Our Project Comes In


In this project, the group will test for bacteria in the two samples of water from both locations being investigated. By investigating the amount of bacteria in the water, the students can have an idea of the water's level of pollution. The chance of finding bacterial life in the samples of water is very big, but what will determine the difference between a clean and a polluted sample is the amount of bacteria found.


Method

1.  After having followed all safety precautions necessary, place 10 cm³ of each sample of water inside a separate, small test tube and place the test tubes inside a centrifuge. Each water type has two samples: one at room temperature and one which has to be previously boiled using a bunsen burner or a kettle.

2.  Centrifuge the samples for 10 minutes.

3.  Get one sample and, with a pipette, carefully add a few drops of the sample of water on top of the agar jelly on a petri dish and seal the petri dish.

4.  Repeat the same process with the other 3 samples of water.

5.  Leave the petri dishes inside an incubator at 37 ^oC for 48 hours.

Results










Conclusion


As it can be clearly seen in the diagrams in the results section, as expected, the boiled samples presented a smaller bacterial growth than the ones kept at normal temperature. But comparing the samples from each site, it can be clearly seen that the sample with the water from the Lagoa Rodrigo de Freitas presented a much larger bacterial growth than the one from Ipanema, which leads us to believe that there is a higher bacterial concentration in the water from Lagoa than the one from Ipanema, and thus, from this variable, it is more polluted.