BIOLOGY INVESTIGATORY PROJECT

ON
STUDY OF ANTIBIOTICS ON MICROBES
BY
NAME – AYUSHEE MEKAP
CLASS – XII ROLLNO-
GROUP – 02
TEAM MEMBERS
Bhumika Mishra
Ishani Ganguly
Dibyasha Rout
Dibyajyoti Mahapatra
 CERTIFICATE
This is to certify that ______________________
of class 12th ‘B’ of Mother’s Public School of
roll no._____ has successfully completed
his/her Biology project file. He/ She has
taken care with utmost sincerity in
completion of his/her project. All the work
related to the project is done by the
candidate himself/herself. The approach
towards the subject has been profound and
scientific.
I certify that this project is up-
to my expectation and as per the
guidelines issued by the CBSE.

PRINCIPAL

INTERNAL EXAMINER EXTERNALEXAMINER

 ACKNOWLEDGEMENT
In the accomplishment of this project
successfully, many people have best
owned upon me their blessings and the
people who have been concerned with this
wholesome project.
Primarily, myself__________________
_________ would thank GOD for being able
to complete this project with success.
Then, I would like to thank our principal
ma’am, Sagufta Parvin and biology
ma’am Subhashree Mishra, whose
valuable guidance has been the ones that
helped me patch this project and make it’s
a FULL PROOF SUCCESS. I would
desperately thank my parents for their
valuable suggestions and superintendence
which served as the MAJOR
CONTRIBUTION towards the completion
of the project.
Lastly, thanks to all my
class-mates who helped me a lot.
INDEX
 INDEX
Introduction
• History and Discovery
• Goals
• How do Antibiotics Work?
• Why are Antibiotics Important?

Resistance
• Antibiotic Resistance
• How Does Resistance Spread?

Types and Mechanism

• 7 Types of Antibiotics
• 5 Basic Mechanism of Antibiotic Action Against Bacteria
Cell

Pros and Cons

• Pros of Taking of Antibiotics
• Side Effects of Taking Antibiotics

Experiment
• Aim
• Materials Required
• Procedure
• Observations
• Conclusion

Bibliography
INTRODUCTION
Antibiotics are chemicals that kill or inhibit the
growth of bacteria and ae used to treat bacterial
infections. They are produced in nature by soil
bacteria and fungi. This gives the microbe an
advantage when competing for food and water
and other limited resources in a particular habitat,
as the antibiotic kills off their competition. Only
substances that target bacteria are called
antibiotics.
• Antiseptics are used to sterilize surfaces of living
tissue when the risk of infection is high, such as
during surgery.
• Disinfectants are non-selective antimicrobial,
killing a wide range of micro-organisms including
bacteria. They are used on non-living surfaces,
for example in hospitals.
 HISTORY AND DISCOVERY

In 1928, at St. Mary Hospital, London, Alexander

Fleming discovered Penicillin. Fleming was, a bit
disorderly in his work and accidently discovered
penicillin. Upon returning from holiday in Suffolk in
1928, he noticed that a fungus, Penicillium notatum,
had contaminated a culture plate of Staphylococcus
bacteria he had accidently left uncovered.
The discovery of penicillin changed the world of
medicine enormously. With its development, infections
that were previously severe and often fatal, like
bacterial endocarditis, bacterial meningitis and
pneumococcal pneumonia, could be easily treated.
Antibiotics were widely used for treating soldiers during
World War Il, caring for battle wound infections and
pneumonia. By the mid-to-late 1940s, it became widely
accessible for the general public.
 GOALS
• To study the effect of antibiotics on micro-
organisms(bacteria).
• To understand its mechanism.
HOW DO ANTIBIOTICS WORK?

Antibiotics are used to treat bacterial

infections. Antibiotics take advantage of the
difference between the structure of bacterial
cell and the host's cell.
They either prevent the bacterial cells from
multiplying so that the bacterial population
remains the same, allowing the host's
defence mechanism to fight the infection or
kill the bacteria, for example stopping the
mechanism responsible for building their cell
walls.
An antibiotic can also be classified according
to the range of pathogens against which it is
effective. Penicillin G will destroy only a few
species of bacteria and is known as narrow
spectrum bacteria. Tetracycline is effective
against a wide range of organisms and is
known as broad spectrum bacteria.
WHY ARE ANTIBIOTICS IMPORTANT?

The introduction of antibiotics into medicine

revolutionized the way infectious diseases were
treated. Between 1945 and 1972, average human
life expectancy jumped by eight years, with
antibiotics used to treat infections that were
previously likely to kill patients. Today antibiotics
are one of the most common classes of drugs used
in medicine and make possible many of the
complex surgeries that have become routine
around the world.
If we ran out of effective antibiotics, modern
medicine would be set back by decades. Relatively
minor surgeries, such as appendectomies, could
become life threatening, as they were before
antibiotics became widely available. Antibiotics are
sometimes used in a limited numbers of patient
before surgery to ensure that patients do not
contact any infections from bacteria entering open
cuts. Without this precaution, the risk of blood
poisoning would become much higher, and many
of the more complex surgeries doctors now
perform may not be possible.
 RESISTANCE
• Antibiotic resistance
Bacteria are termed drug-resistant when they are
no longer inhibited by an antibiotic to which they
were previously sensitive. The emergence and
spread of antibacterial-resistant bacteria had
continued to grow due to both the over-use and
misuse of antibiotics.
Treating a patient with antibiotics causes the
microbes to adapt or die; this is known as 'selective
pressure'. If a strain of a bacteria species acquires
resistance to an antibiotic, it will survive the
treatment. As the bacterial cell with acquired
resistance multiplies, this resistance is passed on to
its offspring. In ideal conditions some bacterial
cells can divide every 20 minutes; therefore after
only 8 hours in excess of 16 million bacterial cells
carrying resistance to that antibiotic could exist.
• How Is Resistance Spread?
Antibiotic resistance can either be inherent or
acquired. Some bacteria are naturally resistance
to some antibiotics due to their physiological
characteristics. This is inherent resistance.
Acquired resistance occurs when a bacterium
that was originally sensitive to an antibiotic
develops resistance. For example, resistance
genes can be transferred from one plasmid to
another plasmid or chromosome, or resistance
can occur due to a random spontaneous
chromosomal mutation.
Types and Mechanism

• 7 TYPES OF ANTIBIOTICS

Although there are well over 100 antibiotics, the

majority come from only a few types of drugs. These are
the main classes of antibiotics.

ANTIBIOTICS EXAMPLE
PENICILLINE Amoxicillin
CEPHALOSPORINS Cephalexin
FLUROROQUINOLONES Ofloxacin
SULPHONAMIDES Bactrim
TETRACYCLINES Tetracycline
MACROLIDES Erythromycin
AMINOGLYCOSIDES Gentamicin
• 5 BASIC MECHANISM OF
ANTIBIOTIC ACTION
AGAINST BACTERIAL CELL

Inhibition of cell wall synthesis (most

common mechanism).
Inhibition of protein synthesis
(translation).
Alteration of cell membranes.
Inhibition of Nucleic acid synthesis.
Antimetabolite activity.

The ribosome is a major target for

Antibiotics. Drugs inhibit ribosome function
either by interfering in messenger RNA
translation or by blocking the formation of
peptide bonds at the peptidyl transferase
centre. These effects are the consequence
of the binding of drugs to ribosomal
subunits.
PROS AND CONS

• PROS OF TAKING ANTIBIOTICS:

1. Antibiotics can slow down the growth of
bacteria and kill many types of infections.
2. In some cases, such as before surgery,
antibiotics can prevent infection from
occurring.
3. Antibiotics are fast acting some will begin
working within a few hours.
4. They are easy to take; most Antibiotics are
oral medications. Your doctor may decide to
give you an injection, if it is imperative that
the medicine gets into your system quickly.
 • SIDE EFFECTS OF TAKING
ANTIBIOTICS:
The most common side effects of antibiotics is- it
affects the digestive system. Antibiotics commonly
cause the following side effects:

1. Diarrhea
2. Nausea
3. Vomiting
4. Rash
5. Upset stomach
6. Sensitivity to sunlight, when taking tetracycline
with certain antibiotics or prolonged use,
fungal infections of the mouth, digestive tract,
and vagina.
EXPERIMENT
• AIM: To see the effect of antibiotics on
bacteria count.
• MATERIALS REQUIRED:
1. 10 test-tubes of sterilized water
2. 10 PCA(Agar) plates
3. Bunsen burner
4. Graduated cylinder
5. Ethanol (Used for sterilizing; just flame is
enough most cases)
6. Glass hockey stick Pipettes
7. Refrigerator
8. Incubator (A warm cabinet for growing
bacteria)
9. Scale
10. Large beaker
11. Hot plate
12. Sample antibiotic
PROCEDURE:
Step 1:
Prepare a culture media plate for growing bacteria.
Step 2:
Get a sample of polluted water for test. Mix 2 ml of
polluted water with 10 ml chicken broth in a test tube
and incubate it for 24 hours so the bacteria will
reproduce and increase. Usually this is done on a
device that constantly moves, so the bacteria can
freely move in the liquid. Most likely you will not have
a vibrator, so it is good if you shake the test tube a few
times during this incubation period.
Step: 3
While the bacteria are being incubated, prepare
some antibiotic disks as described here. (Antibiotic
disks can also be purchased from biology suppliers.)
Break an antibiotic capsule (here using Ampicillin)
and empty the contents in a clean petri-dish. One
capsule will be enough for hundreds of disks. Dispose
of the plastic shell and add a few drops of water to
the remaining powder. Cut some filter papers in small
pieces and soak them in the antibiotic solution. Let
 the disks dry in a clean space. You may cover them
with another filter paper to protect them from dust.

Although they are known as antibiotic disks, you can

cut them in small squares.

The reason that we use filter paper, is that other

papers often have starch and other polymers that may
affect the results of our experiments. Filter paper is
pure cellulose fibre.
Step 4:
Use the bacteria that you have grown in step 2 and
prepare dilution of bacteria.
1. Prepare 1:10 dilution of the sample. To do this, take
2ml of the sample and blend it with 18ml of distilled
water.
2. 2.Pipette 0.1ml of each dilution onto a Plates
Count Agar (PCA) plate.
3. Take a glass hockey stick submersed in ethanol and
run it through a flame to sterilize it. (Glass hockey
stick is a glass rod bent on one end like a hockey
stick. It is used to spread bacteria on the surface of
agar plate. You may use a steel spoon instead.)
4. 4.Let it cool and use it to spread dilution around
the plate.
5. 5.Do this on two plates for each of the five
different dilutions.
6. Place an antibiotic disk on the plate of dilution.
7. 7.1ncubate the plate at 35 degrees Celsius for 24
hours and then count the bacterial colonies.
8. Take 3 nutrient agar plate and added 0.5ml of the
solution on each of plates.
9. Leaving one plate without any antibiotics, placing
one antibiotic disk on the second plate and two
antibiotic disks on the third plate. All plates were
incubated for 48 hours.
OBSERVATIONS:

PCA1

PCA2

PCA3
CONCLUSION:

The growth of bacteria around the antibiotic disks

is less. Inhibition zones are more in the plates with
more antibiotic disks.
Hence, antibiotics stop the proliferation of
bacteria.
BIBLIOGRAPHY
www.emedicinehealth.com
www.microbiologysociety.org
www.scienceproject.com
www.medicalnewstoday.com
www.scribd.com
www.studocu.com