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Field Studies Types of bacteria found around the home

types of bacteria found around the home Bacteria Morphology

Introduction: (Initial Observation)








Project advisor

Information Gathering:

Learn about bacteria, their properties and how they may be classified. Read books, magazines or ask professionals who might know in order to learn about using microscope, sampling bacteria, coloring bacteria, and observing bacteria under the microscope. Also learn about safety methods while handling bacteria and anything else that may help your research. Keep track of where you got your information from.

Following are samples of information that you may find.

There are many different types of bacteria. They differ in the morphology of the cells, their metabolism and chemistry, and the structure of their cell walls. The differences among bacteria are used to classify them and to identify a species. Bacteria come in a number of shapes. Most, however, are cocci (round), bacilli (rod shaped), or spirilla (spirals). The way these individual cells are arranged is also variable among bacterial species. Although some species exist singularly, bacteria can be linked together in a long chain (strepto-), clumped like grapes (staphylo-), paired (diplo-), and can exist in other arrangements as well. Bacteria also differ in structure, particularly in the composition of their cell walls. The internal chemistry and metabolism of bacteria also demonstrates the diversity among bacteria, as species differ in their ability to use and process various nutrients and produce different waste products.

Staining is the method used to determine the cell wall structure in bacteria. (PA)

There are different kinds of stain. In the Gram stain, differences in bacterial cell wall structure lead to either a positive or negative Gram reaction. Bacteria that give a positive Gram reaction have thick cell walls composed of peptidoglycan (consists of polymers of modified sugars cross linked by short polypeptides that vary), retain the initial stain and appear in violet color under a microscope. Bacteria with a negative Gram reaction have a thin peptidoglycan cell wall and have an additional outer membrane of lipopolysaccharides (carbohydrates bonded to lipids). This structure causes the cell to be easily decolorized, and the bacteria will appear reddish pink, the color of the counter stain. The Gram reaction of a bacteria is highly related to the biochemistry of the species. The difference in cell wall structure between Gram negative and Gram-positive bacteria conveys distinct characteristics to the bacteria, giving them different properties, different capabilities, and different requirements for survival. Which also helps classify the bacteria. The peppercorn infusion (will be observed, and Mungbean infusion) served as a good medium for bacteria growth because of the high concentrations of organic molecules dissolved in the water.


Three general shapes of bacteria:

(coccus, plr. cocci)
(bacillus, plr. bacilli)
(spirillum, plr. spirilla)
Example:Staphylococcus epidermidis Example: Escherichia coli Example: Treponema pallidum




The structure of bacteria:

Bacteria are single cell organisms. Their cells are Prokaryotic, meaning that they lack a membrane-bound nucleus and many of the cell parts of Eukaryotes (Cells that have a nucleus and many membrane-bound organelles). Some of their parts:

1. Capsule – outside protective layer usually found on disease causing bacteria

2. Cell Wall – next layer in that gives bacteria their shape and additional durability.

3. Cell Membrane (plasma membrane) – permeable membrane that has a variety of functions, including bringing chemicals and nutrients in and out of the cell.

4. Cytoplasm – gel-like material inside cell that protects cell parts and helps move materials around the cell.

5. Ribosomes – make various proteins

6. DNA – genetic material that controls the functions of the cell. The “genes” of the organism.

7. Flagella – a tail used to move around. Some have many and some have none.

8. Pilus (Cillia)– small hairs used for sticking to surfaces of each other. Also used in reproduction. Some have many, some have none.

There are different types of bacteria , so it would be difficult to classify them into a particular group. The best way to classify bacteria would be based on their environmental and nutritional requirement. Most bacteria can be placed into one of three groups based on their response to oxygen, namely;


These are bacteria which thrive in the presence of oxygen and require oxygen for their continued growth and existence.


These bacteria on the other hand cannot tolerate gaseous oxygen. Examples of such bacteria are those bacteria which live in deep underwater sediments or those which cause food poisoning.

Facultative Anaerobes

These are the third type of bacteria which prefer growing, in the presence of oxygen but can continue to grow without it. They are very flexible, hence can exist anywhere.

Bacteria may also be classified according to their source of energy. Classification based on the mode by which bacteria obtain their energy falls into two categories;


These bacteria derive their energy from breaking down complex organic compounds that they must take in from the environment. Example of these bacteria are saprobic bacteria found in decaying material, as well as those that rely on fermentation or respiration.


These type of bacteria fix carbon dioxide to make their own food source, and this may be fueled by light energy (photoautotrophic), or by oxidation of nitrogen, sulfur or other elements. Photoautotrophs are very common and quite diverse such as cyanobacteria, green sulfur bacteria, purple sulfur and non purple sulfur bacteria.

Usefulness of Bacteria

To the layman, the word bacteria denotes germs, disease-causing organisms and anything that causes infection. But there’s more to bacteria than that, in fact disease-causing bacteria forms only a tiny fraction of the species. Bacteria has a lot of benefits to humans. The benefits are enormous and covers a lot of fields from agriculture to nutrition. The usefulness of bacteria cannot be over-emphasized.
Harmless and beneficial bacteria are far more than the harmful bacteria. Due to their capability of producing so many enzymes necessary for the building up and breaking down of organic compounds, bacteria are extensively used in :

Soil Enrichment

A very important activity of bacteria is the cycling of nitrogen. Plants rely on nitrogen from the soil for their health and growth, and cannot acquire it from gaseous nitrogen in the atmosphere. Nitrogen fixing bacteria convert gaseous nitrogen into nitrates or nitrites as part of their metabolism, and the resulting products are released into the environment. This process is known as nitrogen fixation and examples of nitrogen fixing bacteria are Rhizobium, cyanobacteria such as Anabaena, Nostoc, and Spirulina . They turn nitrogen from the air into protein via the roots of legumes such as peas, clover and peanuts.

Preservation and Fermentation

Bacteria preserves certain food items by making it’s environment, our food, acidic. A special bacterium that does this is called Lactobacillus acidophilus. Bacteria is also widely used in fermentation (as in the manufacture of alcoholic beverages, vinegar and certain dairy products). During fermentation, theses bacteria make acids as a by-product thereby making the environment toxic to other microbes which might be harmful to the food.


This is the breakdown of dead and/or rotting organisms, and the release of nutrients back into the environment. This is one of the most important roles of bacteria because organic carbon in the form of dead & rotting organisms would quickly deplete the carbon dioxide in the atmosphere if not for the activity of decomposers. Bacteria are also used for decomposing organic waste such as: in septic tanks and some sewage disposal plants as well as in agriculture (soil enrichment).


Harmful Bacteria

Bacterial parasites that cause disease are called pathogens. Among bacterial plant diseases are leaf spot, fire blight, and wilts; animal (e.g humans) diseases caused by bacteria include tuberculosis, cholera, syphilis, typhoid fever, and tetanus. Some bacteria attack the tissues directly; others produce poisonous substances called toxins.

Natural defense against harmful bacteria is provided by antibodies. Certain bacterial diseases, e.g., tetanus, can be prevented by injection of antitoxin or of serum containing antibodies against specific bacterial antigens; immunity to some can be induced by vaccination; and certain specific bacterial parasites are killed by antibiotics. New strains of more virulent bacterial pathogens, many of them resistant to antibiotics, have emerged in recent years. Many believe this to be due to the overuse of antibiotics, both in prescriptions for minor, self-limiting ailments and as growth enhancers in livestock; such overuse increases the likelihood of bacterial mutations. For example, a variant of the normally harmless Escherichia coli has caused serious illness and death in victims of food poisoning.

Question/ Purpose:


The purpose of this project is to find out how many different types of bacteria may be found in different locations around the home. Types of bacteria can be determined by the color and shape of their colonies. Locations such as the kitchen sink, Kitchen counter, refrigerator handle, door knobs, toilet bowel and computer keyboard will be tested.

Identify Variables:


The independent variable (also known as manipulated variable) is the location where the bacteria is found.

Dependent variable (also known as responding variable) is the number of bacteria types in each location.

Controlled variables are sampling and observation methods.



Since bacteria grow best in moist warm environment, Kitchen sink is supposed to have the largest variety of bacteria.

Experiment Design:



Collect samples of bacteria from different places in your house and observe them under the microscope. Record the shapes of bacteria and the concentration of bacteria of each type.


    1. Select the spaces that you want to get samples from. Mark an area of about one square inch in that space. Wet a q-tip with distilled water and then rub it all over the marked area. In a small test tube or in a cavity of a cavity plate, place one mL distilled water and then use the q-tip to stir that water. Squeeze the wet Q-tip to the sides of the cavity to force the bacteria out of the Q-tip and into the water. Number the test tube (or cavity) and record it in your log file. Dispose of the q-tip.
    2. Repeat the above process with every location that you have in mind. Kitchen Sink, Refrigerator door handle, Kitchen counter top, Computer mouse or keyboard, and doorknobs are among the places that you may want to test.
    3. Place a drop of liquid dye in each tube, shake it so the die mixes with water. Let the mixture sit for about 5 minutes. This gives enough time to the bacteria cell membrane to absorb the dye.
    4. Get some clean microscope slides and slide covers. Number them with the same numbers used for your samples. Place one drop of each sample on the center of the microscope slide and then cover it with a microscope slide cover.
    5. Place each slide under the microscope with magnification of 400. Make necessary adjustments of light and focus the image. Look for same size, same shape organisms, count them and record your results. Following is a sample blank results table:
Location Round/ Coccus Rod/ bacillus Spiral/ spirillum
1- Kitchen sink
2- Kitchen counter top
3- Dorr Knob
4- ……….

The numbers in the above table show the number of bacteria visible on the center of the slide. That area usually is a circle with the diameter of 1/2 millimeter; however, with a 400X magnification, we see it like a circle with diameter of 10 centimeters.

What about the control?

Any scientific experiment needs a control. Someone may ask you “How do you know that the bacteria are from the test surface? They may also be from the distilled water or from the q-tip. That is why you will also need a control experiment to eliminate such doubts. In your control experiment you do everything as you do with your test surface; however, you skip the rubbing action. In other words you just use a clean q-tip and distilled water. every other step will be exactly the same.

The results of your control experiment can fill one of the rows in your results table. In the location column write control. What you write in other columns depend on your observation.

Materials and Equipment:

List your material and equipment in this section of your report. Following is a sample:

    1. Microscope with 400X magnification
    2. 20 Microscope slides
    3. 20 Microscope slide covers
    4. 20 disposable Transfer pipettes
    5. Dye for bacteria.
      (Dyes for bacteria are usually known as Microscope Slide Stain. Some readily available stains are: food coloring, iodine, malachite green (ick fish cure), and methylene blue. Food coloring can be found at a grocery store, and iodine can be found at a pharmacy. The last two stains, malachite green and methylene blue, can be purchased at aquarium shops.)
    6. Hand counter

Results of Experiment (Observation):



You may optionally do some calculations to determine the number of bacteria in each square inch of your test locations. If you do, please write your calculations in this part of your report.

Summary of Results:



Write an abstract:

An abstract is a short statement that summarizes the purpose, methods, and findings of your research project. It should be a single paragraph that grabs the reader’s attention. Writing the abstract is the last part of your project; however, you must place your abstract as the first part of your project report.



Related Questions & Answers:


Possible Errors:




Before starting your field study, it is necessary to do your own research and study about bacteria and their different types. Biology books and the Internet are good sources for such studies. The links below can be used to complement your work.