Effect Of Antibiotics On Microorganisms.pdf

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EFFECT OF ANTIBIOTICS ON  MICROORGANISMS  09.04.2019 

Shrishti  XII-B 

Mount carmel school  Dwarka sec-22  New delhi 

Overview  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 microbe an advantage when competing for food and water and other limited resources in a  

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particular habitat, as the antibiotic kills off their competition.​Only substances that target bacteria are called antibiotics. ● Antiseptics are used to sterilise surfaces of living tissue when the risk of infection is high, such as during surgery. ● Disinfectants are non-selective antimicrobials, killing a wide range of micro-organisms including bacteria. They are used on non-living surfaces, for example in hospitals.

Goals  1. To study the effect of antibiotics on micro-oraganisms (bacteria).  2. To understand it’s 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 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 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 revolutionised 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

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were before antibiotics became widely available. Antibiotics are sometimes used in a limited numbers of patients before surgery to ensure that patients do not contract 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   

I.

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 has 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 bacterial 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

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every 20 minutes; therefore after only 8 hours in excess of 16 million bacterial cells carrying resistance to that antibiotic could exist.  

II.

How is resistance spread?

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

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.

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ANTIBIOTIC

EXAMPLE

PENICILLIN

amoxicillin

CEPHALOSPORINS

cephalexin

MACROLIDES

erythromycin

FLUOROQUINOLONES

ofloxacin

SULFONAMIDES

bactrim

TETRACYCLINES

tetracycline

AMINOGLYCOSIDES

gentamicin

EXPERIMENT  AIM:​ ​to see the effect of antibiotics on bacteria count. ​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



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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 (I used ​Ampicilin​) 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.

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  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 fiber. Step 4: ​ se the bacteria that you grown in step 2 and prepare dilution of U bacteria. 1. Prepare 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 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 plate and added 0.5 ml of the solution on each of plates. I left one plate without any antibiotics, placed one antibiotic disk on the second plate and two antibiotic disk on the third plate. All plates were incubated for 48 hours.

OBSERVATIONS: PCA1

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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 proliferation of bacteria.

BIBLIOGRAPHY: www.emedicinehealth.com  Microbiologysociety.org  www.scienceproject.com       


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