What Disinfectant is Most Effective Against Bacteria?

Researched by Austin H.


The purpose of this experiment was to determine which antiseptic works best against specific bacteria.

I became interested in this idea when I was on medication for a sickness and noticed how much the medication costs and its side effects.  The information gained from this experiment might prevent people from getting sick if household items will kill sickness-causing bacteria around the house.  It could prevent society from the wasting of time and money for doctor visits, buying prescription medicine and paying medical bills.


My hypothesis is that isopropyl alcohol will work better than ammonia and Lysol.  I base my hypothesis on the fact that isopropyl alcohol is used in hospitals and doctors’ offices for antiseptic purposes before administrating injections.


 The constants in this study were:
 The same kind of bacteria was used in all tubes and Petri dishes.
 The flasks were the same size and shape.
 The same amount and type of agar was used in each tube and Petri dish.
 The same method of separating bacteria was always used.
 Measurements were made in the same manner.
 Temperature, humidity and light were the same for all tubes and Petri dishes.
 The same quantity of disinfectants was used in all tubes and Petri dishes.
 The disinfectants touched bacteria the same amount of time.
 The time of day of observation was almost the same.
 The method of recording observations was consistent.

The manipulated variable was the type of antiseptic.

The responding variable was the amount of bacteria growth in the flacks during a 3-day period of time.

Measure the responding variable by recording the number of colonies in each Petri dish in each group.  This will determine which antiseptic is most effective, how much of each of the original bacteria is eliminated and how fast does it reproduce after being exposed to the antiseptics.

Unit of bacteria (Lactos Bacillus)
 Petri dishes preloaded with agar
 Test tubes
 Bottle of isopropyl (rubbing) alcohol (70%)
 Bottle of ammonia
 Bottle of Lysol
 Box of rubber gloves
 Pad of paper
 Hours to conduct the experiment



1. Gather all materials needed.
2. Add bacteria to culture flask.
3. Let stand for 24 hours.
4. Label 1 test tube C.
5. Label four more test tubes: 2a, 2b, 2c and 2d.
6. Label four more test tubes: 3a, 3b, 3c and 3d.
7. Label the last four test tubes: 4a, 4b, 4c and 4d.
8. Add 50ml of bacteria infested water to each test tube.
9. Set the control test tube aside which will have no antiseptic added.
10. Measure out 5ml of ammonia and add it to flask 2a.
11. Measure out 10ml of ammonia and add it to flask 2b.
12. Measure out 15ml of ammonia and add it to flask 2c.
13. Measure out 20ml of ammonia and add it to flask 2d.
14. Let flasks stand for two minutes.
15. Label the Petri dishes the same as the test tubes.
16. Add 1ml of each tube contents to each Petri dish labeled the same.
17. Measure 5ml of isopropyl alcohol and add it to flask 3a.
18. Measure 10ml of isopropyl alcohol and add it to flask 3b.
19. Measure 15ml of isopropyl alcohol and add it to flask 3c.
20. Measure 20ml of isopropyl alcohol and add it to flask 3d.
21. Let flasks stand for two minutes.
22. Add 1ml of each tube contents to each Petri dish labeled the same.
23. Measure 1ml of Lysol and add it to flask 4a.
24. Measure 5ml of Lysol and add it to flask 4b.
25. Measure 10ml of Lysol and add it to flask 4c.
26. Measure 20ml of Lysol and add it to flask 4d.
27. Let flasks stand for two minutes
28. Add 1ml of each tube contents to each Petri dish labeled the same.
29. Set incubator to 34 degrees Celsius.
30. Place all Petri dishes into the incubator.
31. Observe 72 hours from incubating and proceed with a colony count under a microscope.


The original purpose of this experiment was to determine which antiseptic works best against specific bacteria.  The isopropyl alcohol did not even affect the bacteria at 5ml, disinfected 1/3 of them in the 10ml and totally killed them in the 15ml and 20ml.  The ammonia proved to be less affective and barely disinfected at all.  5ml and 10ml didn’t work at all, 15 and 20ml did but almost too small to notice. Lysol was the most effective even after being deluded to the recommended concentration it disinfected the samples entirely in all of the amounts


My hypothesis is that isopropyl alcohol will work better than ammonia and Lysol.
The results indicate that this hypothesis should be rejected because the Lysol worked far better then the ammonia and the alcohol.
Because of the results of the experiment I wonder if the company that manufactures Lysol should create a product that hospitals could use on patients instead of isopropyl alcohol.
If I were to conduct this project again I would use antibacterial soap in my experiment and I also would have been more prepared for the scientific committee.  I would of also of used two strands of bacteria to see if my results are more widely occurring.


Bacteria are microorganisms that lack cell membranes.  Scientists believe they are the oldest living things on earth.  Bacteria are less than one micron in length (.0001 mm).  Hundreds of thousands of bacteria can fit in the period at the end of this sentence.  Bacteria can multiply at an incredible rate if they can get enough food.  Within a few days, multimillion colonies can be seen with ease without the aid of a microscope.


There are two distinct kinds of life: procaryotic and eucaryotic.  Procaryotes are things that are microscopic and do not have internal membranes.  Eucaryotes are macro or microscopic and have internal compartments.

Bacteria are also classified by shape.  If the shape is spherical, it is called a cocci.  A rod-shaped bacteria is a bacilli and a corkscrew is called a spirochetes.

Bacteria are also be classified by whether they need oxygen.  Bacteria that need oxygen to survive are aerobic bacteria and those that do not need oxygen are anaerobes.

One last way of classifying bacteria is by the method used to obtain carbon and energy.  Autotrophs obtain their carbon from carbon dioxide and their energy from different things.  Photoautrotrophs get their energy from light and use the process called photosynthesis for their energy.  Photosynthesis uses light to change substances into matter on which the bacteria can feed.  The remaining bacteria are called heterotrophs.  They receive their carbon from eating organic molecules.  There is a subspecies called photoheterotrophs, which obtain their energy from the sun.


In the later part of the 1600’s, Antoni van Leeuwenhoek was the first person to study bacteria.  He became the inventor of the microscope.  Other great microbiologists of the past include Robert Koch, the person who showed us some bacteria can cause disease; and Selman Waksman, who found a large variety of soil bacteria and who also produced antibiotics that completely revolutionized the way we treat bacteria and disease.


Like all cells, bacteria contain DNA, but unlike most cells it is in a circular pattern instead the normal helix shape.  Many bacteria have small limbs extending from their membranes called pilus.  Pilus are hair-like teeth that can attach to rocks, prey and many other things.  Other have extensions called flagella.  They use these extensions to propel themselves toward nutrients.


Bacteria reproduce by a process known as binary fission.  They basically split into two separate life forms.  When these two new bacteria reach full size and maturity, they again split and so the process continues.

How Bacteria Affect Our Daily Lives

Bacteria cover almost every natural surface known to man and live inside many plants and animals.  Bacteria are very important in the survival of the ocean ecosystem.  Bacteria are at the bottom of the food chain.  They are eaten by plankton, which is eaten by larger animals, which are, in turn, eaten, etc.  Bacteria are also important removers of waste.  They feed on dead and decaying animals and other wasters, turning them into valuable soil.

History of Soap

Soap is a cleaning agent that is made of animal and plant fats and the sodium or potassium salt in the fatty acid, which is formed by the interaction of the fats and alkali.  The first soap was talked about in the Old Testament.  This was not true soap but was made from just tree bark ashes alone.  The 1200’s introduced the soap industry to France.  Most soap was made of goat tallow with beech ash.  The French then found how to made soap out of olive oil.


Bacteria are a small but important part of our world.  Scientists believe they have been on Earth longer than any other life form.  The means to control disease-causing bacteria is essential for the health of mankind but a balance must be struck.  Bacteria as a life form must never be threatened because they are one of the basic corner stones on which the delicate balance of nature is built.  Without bacteria, life as we know it would cease to exist.


“Bacteria” Macropedia Britannica, (1988).

“Bacteria” Microsoft Encarta, (1998).

“Bacteria” Microsoft Encarta, (1999).

Carter, Joseph, et al. Life Science Ginn and Company, (1971).

“Detergents” Microsoft Encarta, (1999).

Dravistion, Michael. Microbiology Warner Books. (1987).

“Soap” Microsoft Encarta, (1999).

Schessinger, David. “Bacteria” World Book Encyclopedia. (1994)

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