SHIRINBAI NETERWALA SCHOOL

Maneck Nagar, Tumsar

Department of Biology
(Science)
A
Project Report
On
Study of the effect of antibiotics on micro-organism

Submitted By:
Miss Anshika Singh
Class XII – (Science)

Guided By:
Mr. Yuvraj Sonewane
 SHIRINBAI NETERWALA SCHOOL
Maneck Nagar, Tumsar

CERTIFICATE

This is to certify that Miss Anshika Singh completed his/her practical

work for class 12- Science of subject Biology (044) during the

academic year 2022-2023 prescribed by CBSE Board under the

supervision of Mr. Yuvraj Sonewane.

Guided By External Examiner Principal

ACKNOWLEDGEMENT
I would like to express my special thanks of gratitude towards our

biology teacher Mr. Yuvraj Sonewane sir as well as our lab assistant

Mr. M.S.Chandel sir who helped and guided me to do the project on

the topic “Study of the effect of antibiotics on micro-organisms.”

While researching this project I came to know about new things due

to which my knowledge regarding this topic also increased. This is

only because of the teacher who gave me this amazing project, I am

thankful to them.

I am drafting this project not only for good marks but it is also to

increase my creativity, and skill in doing the project and to enhance

my knowledge about this topic.

I also want to express my deep gratitude and sincere to our principal

Mr. P Bimal sir hating for this encouragement and for all facilities that

he provides for this project.

CONTENTS
 Certificate
 Acknowledgement
 What are antibiotics?
 Objective
 How do antibiotics work?
 Why are antibiotics important?
 Resistance
 Antibiotics resistance
 How is resistance spread?
 Types of antibiotics
 Experimental Work
 Aim
 Materials required
 Procedure
 Observations
 Result
 Precaution
 Conclusion
 Bibliography
WHAT ARE ANTIBIOTICS?

Antibiotics are chemicals that kill or inhibit the growth of bacteria and are
used to treat bacterial infections. They are produced in nature by soil bacteria
and fungi. This gives the microbes an advantage when competing for food
and water and other limited resources in a particular habitat, as the antibiotics
kill off competition. Only substances that target bacteria are called antibiotics.

Antiseptics are used to sterilize the surfaces of living tissue when the risk of
infection is high, such as during surgery.

Disinfectants are non-selective antimicrobials, that kill a large range of

microorganisms including bacteria. They are used on non-living surfaces, for
example, hospitals.
The first modern-day antibiotic was used in 1936. Before antibiotics, 30% of
all deaths in the united states were caused by bacterial infections. Thanks, to
antibiotics, previously fatal infections are curable.

Today, antibiotics are still powerful, lifesaving medications for people with
certain serious infections. They can also prevent less serious infections from
becoming serious.

There are many classes of antibiotics. Certain types of antibiotics work best
for specific types of bacterial infections.

Antibiotics come in many forms, including:

 Tablets
 Capsules
 Liquids
 Creams
 Ointment

OBJECTIVE

1. To study the effect of antibiotics on microorganisms (bacteria).

2. 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 the 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 defense 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 a narrow-spectrum antibiotic. Tetracycline is
effective against a wide range of organisms and is known as a broad-
spectrum antibiotic.

WHY ARE ANTIBIOTICS IMPORTANT?

The introduction of antibiotics into medicine revolutionized the way infectious

diseases were treated. Between 1945 and 1972, the 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 become widely available.
Antibiotics are sometimes used in a limited number of patients before surgery
to ensure that patients do not contract any infections from bacteria entering
open cuts. Without precaution, the risk of blood poisoning become higher,
and many of the more complex surgeries doctor now perform may not be
possible.
RESISTANCE
1. ANTIBIOTICS 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 have continued to grow due to both the
overuse 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 bacterial species acquires
resistance to antibiotics, 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, over 16 million bacterial cells carrying resistance to that
antibiotics could exist.
HOW IS RESISTANCE SPREAD?

Antibiotic resistance can either be inherent or acquired. Some bacteria are

naturally resistant to 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 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:

ANTIBIOTIC EXAMPLE
 1. Penicillin Amoxicillin
2. Cephalosporins Cephalexin
3. Macrolides Erythromycin
4. Fluoroquinolones Ofloxacin
5. Sulfonamides Bactrim
6. Tetracyclines Tetracycline
7. Aminoglycosides Gentamicin

EXPERIMENT

AIM: Study of the effect of antibiotics on micro-organisms

MATERIALS REQUIRED
 10 test tubes of sterilized water
 10 PCA(Agar) plates
 Bunsen burner
 Graduated cylinder
 Ethanol (used for sterilizing. Just flame is enough in most cases)
 Glass hockey stick
 Pipettes
 Refrigerator
 Incubator (a warm cabinet for growing bacteria)
 Microwave
 Scale
 Large beaker
 Hot plate
 Sample antibiotic

PROCEDURE:
Step 1:
Prepare a culture media plate for growing bacteria.

Step 2:
Get a sample of polluted water for the 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
produce 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 (I used
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 into small pieces and soak
them in the antibiotic solution. Let the disks dry
in a clean space. You may cover them with
filter paper to protect them from dust.
Dispose of the plastic shell and add a few drops of water to the remaining
powder. Cut some filter papers into small pieces
and soak them in the antibiotic solution. Let the
disks dry in a clean space. You may cover them
with filter paper to protect them from dust.

Step 4:
Use the bacteria that you grew in step 2 and prepare a dilution of the
bacteria.
1. Prepare a 1:10 dilution of the sample. To do this, take 2 mL of the sample
and blend it with 18 mL of distilled water.
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 the agar plate. You may
use a steel spoon instead.)
4. Let it cool and use it to spread dilution around the plate.
5. Do this on two plates for each of the five different dilutions.
6. Place an antibiotic disk on the plate of dilution.
7. incubate the plate at 35 degrees Celsius for 24 hours and then count the
bacterial colonies.
8. take 3 nutrient agar plates and added 0.5 ml of the solution on each of the
plates. I left one plate without any antibiotics, placed one antibiotic disk on the
second plate, and two antibiotic disks on the third plate. All plates were
incubated for 48 hours.
OBSERVATION:
PCA1

PCA2

PCA3

PRECAUTIONS:
 Do not expose the culture of the Petri dish to the atmosphere
 Sterilize the Petri dishes properly in the oven before use
 Use proper kind of stains for different types of microorganisms.

RESULT:
Penicillin and Terramycin were the most effective antibiotic against
microorganisms in the soil with Streptomycin and Chloromycetin not too far
behind. The surviving colonies of microorganisms in the Petri dish may have
developed a resistance to the stated antibiotics and there is a high possibility
that the antibiotic would be less and less effective on future generations of
the surviving colonies

PRECAUTIONS:
Several important steps can be taken to ensure proper and effective antibiotic
use.
 Take antibiotics only for bacterial infections. Don’t use antibiotics for
conditions caused by viruses such as the common cold, flu, cough, or sore
throat.
 Take antibiotics as directed by a healthcare professional. Using the wrong
dose, skipping doses, or taking it longer or shorter than directed might
contribute to bacterial resistance. Even if you feel better after a few days, talk
with your healthcare professional before discontinuing an antibiotic.
 Take the right antibiotic. Using the wrong antibiotic for an infection might
lead to resistance. Don’t take antibiotics prescribed for someone else. Also,
don’t take antibiotics left over from a previous treatment. Your healthcare
professional will be able to select the most appropriate antibiotic for your
specific type of infection.

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:
1). Website
www.emedicinehealth.com
Microbiologysociety.org
www.scienceproject.com
2). Books
NCERT Textbook Class 12
Comprehensive Practical Manual