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MCQs on Antibiotics

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Introduction To Antibiotics

IVSAT 2024

Antibiotics are drugs that are used to treat bacterial infections. They do this by either killing the bacteria or preventing them from replicating or duplicating themselves. Antibiotic means "against life." An antibiotic is a medication that destroys microorganisms in the body. However, most people use the phrase to refer to antibiotics that are used to kill microorganisms. Many individuals died from mild bacterial illnesses like strep throat before antibiotics were discovered in the 1920s. Surgery was also more dangerous. However, as antibiotics were accessible in the 1940s, life expectancy grew, operations became safer, and individuals were able to survive previously fatal illnesses.


Classification of Antibiotics:

  • On the basis of chemical structure

  • On the basis of origin

  • On the basis of range of activity ( spectrum of activity)

  • On the basis of mode of action

  • On the basis of effects of their activity

  • On the basis of route of administration


Natural Antibiotics:

Honey is one of the oldest antibiotics known, dating back to ancient times. Egyptians utilize honey as a natural antibacterial and skin protectant. Honey contains hydrogen peroxide, which could explain some of its antimicrobial properties.


Semi-synthetic antibiotics, such as Penicillin V, contain an original chemical molecule from a microorganism but have been further altered. 


Synthetic antibiotics, such as cephalosporins, are made entirely in a laboratory.

Antibiotics are further categorised based on which germs they are effective against or their antibacterial spectrum. Broad-spectrum medicines are antibiotics that are effective against both gram positive and gram negative microorganisms. It is possible to remove pathogens with wide spectrum antibiotics without first running laboratory tests to identify the individual pathogen implicated, thus treatment must identify the exact pathogen involved. Narrow spectrum antibiotics are another type of antibiotic.


Mode of action of antibiotics:

The modes of action of antibiotics can be classified on the basis of the target site and, to some extent, to the alterations in structure produced.It is characterized by their action on the ribosome, resulting in the alteration of protein synthesis. Some antibiotics function by attaching to components involved in DNA or RNA synthesis, interfering with normal cellular processes and, as a result, compromised bacterial proliferation and survival. Quinolones, metronidazole, and rifampin are other examples.


Bactericidal and bacteriostatic antibiotics:

Bacteriostatic antibiotics limit bacterial growth but do not harm cells, whereas bactericidal antibiotics kill bacteria. The infection must subsequently be cleared by the human immune system.


Antibiotics are divided into various categories. These can operate on entirely distinct bacterial targets or the same target in a different location. In principle, bacteria have three major antibiotic targets:


  • The bacterial cell is surrounded by a cell wall or membranes.

  • The equipment used to create the nucleic acids DNA and RNA.

  • The equipment used to make proteins (the ribosome and associated proteins).


These targets are missing or different in human and other mammalian cells, suggesting that antibiotics do not affect our cells and are bacteria-specific. Antibiotics, on the other hand, might have undesirable side effects in some circumstances.


Application Of Antibiotics

Antibiotics are prescribed by a doctor to treat bacterial infections. It doesn't work against viruses. Knowing whether an illness is bacterial or viral might help you to treat it more successfully. Most upper respiratory tract infections (URTIs), such as the common cold and flu, are caused by viruses. Antibiotics do not affect these viruses.


Bacteria may grow resistant to antibiotics if they are overused or used inappropriately. This means that when the bacterium's defences increase, the antibiotic becomes less effective against that type of bacterium. A broad-spectrum antibiotic can be prescribed by a doctor to treat a variety of ailments. Only a few species of bacteria are effective against a narrow-spectrum antibiotic.


Some antibiotics are effective against aerobic bacteria, whereas others are effective against anaerobic bacteria. Anaerobic bacteria do not require oxygen, whereas aerobic bacteria do.


1. In Which of the Following Substances is Chlortetracycline Soluble:

(a) Water

(b) Ether

(c) Organic solvents

(d) All of the above

Answer: Water


2. Cell-wall Biosynthesis is Inhibited by Antibiotics by Inhibiting the Biosynthesis of Which of the following?

a) lipopolysaccharide

b) cellulose

c) peptidoglycan

d) proteins

Answer: Peptidoglycan


3. Bacterial Cells Grown in a Medium Exposed to High Osmotic Pressure, Changes Shape from Rod-shaped to __________ Shaped.

a) spherical

b) rod-shaped

c) irregular

d) elongated

Answer: Spherical


4. Which Among of the Following Antibiotics Act as Folate Antagonist:

a) Penicillin

b) Tetracycline

c) Trimethoprim

d) Cefotaxime

Answer: Trimethoprim


5. Which Among the Following Antibiotics Function as Protein Synthesis Inhibitors:

a) Penicillin

b) Tetracycline

c) Cefotaxime

d) Trimethoprim

Answer: Tetracycline


6. At Normal the pH Value of Penicillin Remains in Which Form:

a) Solvent phase

b) Precipitates

c) Aqueous phase

d) Both (a) and (b)

Answer: Aqueous phase


7. Which of the Following Antibiotics Functions as Cell Wall Inhibitors:

a) Penicillin

b) tetracycline

c) trimethoprim

d) Ciprofloxacin

e) Cefotaxime

Both a and e

a, c and d

c, d and e

All of the above

Answer: a and e


8. Which of the Following Antibiotics is Effective in treating oral Candidiasis:

a) Nystatin

b) Bacitracin

c) Tetracycline

d) Griseofulvin

Answer: Nystatin


9. In Which of the Following Substances is Chlortetracycline Soluble:

a) Water

b) Ether

c) Organic solvents

d) All of the above

Answer: Water


10. The Crystalline Sodium or Potassium Salts are Slightly Soluble in:

a) ether

b) dioxane

c) water

d) chloroform

Answer: Chloroform


11. Which of the Following Antibiotics is Most Likely to Cause Depression of the Bone Marrow:

a) Streptomycin

b) PencillinG

c) Tetracycline

d) Trimethoprim

e) Amphotericin B

Answer: Amphotericin B


12. Which of the Following Does not Affect the Activity of Penicillin?

a) Bile

b) Hydrochloric acid

c) Cysteine

d) Sodium hydroxide

Answer: Bile


13.  Benzylpenicillin is the Chemical Name for Which of the Following Penicillin?

a) Penicillin G

b) Penicillin V

c) Penicillin F

d) Phenethicillin

Answer: Penicillin G


14.  Which of the Following Does not Affect the Activity of Penicillin?

a) Bile

b) Hydrochloric acid

c) Cysteine

d) Sodium hydroxide

Answer: Bile


15. Streptomyces Orientalis Produces Which of the Following Antibiotics?

a) Cephalosporins

b) Cycloserine

c) Bacitracin

d) Vancomycin

Answer: Vancomycin


16. Which of the Following Fermentation Processes is Used in the Production of Penicillin?

(a) Aerobic fermentation followed by anaerobic fermentation

(b) Anaerobic fermentation

(c) Aerobic fermentation

(d) Anaerobic fermentation followed by aerobic fermentation

Answer: Aerobic fermentation


17. Which of the Following Interferes with the Regeneration of the Monophosphate Form of Bactoprenol from the Pyrophosphate Form?

a) Vancomycin

b) Ampicillin

c) Bacitracin

d) Cephalosporins

Answer: Bacitracin


18. After the Fermentation Process, Penicillin is Recovered as

a) Penicillin

b) Sodium penicillin

c) Calcium penicillin

d) Potassium penicillin

Answer: Potassium penicillin


19. Streptomycin is Produced by Which of the Following Organisms?

a) Streptomyces noursei

b) Streptomyces nodosus

c) Streptomyces fradiae

d) Streptomyces griseus

Answer: Streptomyces griseus


20.  Tyrocidines are More Effective Against Which Organism:

a) Gram-positive organisms

b) Gram-negative organisms

c) Mycoplasmas

d) Spirochetes

Answer: Gram-positive organisms


21. Multiple Drug Resistance is Most Closely Related to Which of the following: 

a) Plasmids

b) Viruses

c) Transformation

d) Cell chromosome

Answer: Plasmids


22. Which of the Following Penicillin has Bes Gram-Negative Spectrum:

a) Nafcillin

b) Ampicillin

c) Methicillin

d) Penicillin V

Answer: Ampicillin


23. Cell-wall Biosynthesis is Inhibited by Antibiotics by Inhibiting the Biosynthesis of Which of the following?

a) Lipopolysaccharide

b) Cellulose

c) Peptidoglycan

d) Proteins

Answer: Peptidoglycan


24. What is the Typical Drug of Choice for Most Orofacial Infection:

a)  Penicillin

b) Tetracycline

c) Trimethoprim

d) Ciprofloxacin

Answer: Penicillin


25. The High Yield of Chlortetracycline Requires Which Among the Following:

(a) No aeration

(b) Controlled aeration

(c) Continuous aeration

(d) Aeration which does not affect the yield

Answer: Continuous aeration


26. Which of the Following Interferes with the Regeneration of the Monophosphate Form of Bactoprenol from the Pyrophosphate Form:

a) Vancomycin

b) Ampicillin

c) Bacitracin

d) Cephalosporins

Answer: Bacitracin


27. Streptomycin is Produced by Which of the Following Organisms?

a) Streptomyces noursei

b) Streptomyces nodosus

c) Streptomyces fradiae

d) Streptomyces griseus

Answer: Streptomyces noursei


28.  Tyrocidines are More Effective Against:

a) Gram-positive organisms

b) Gram-negative organisms

c) Mycoplasmas

d) Spirochetes

Answer: Gram-positive organisms


29. Which of the Following Events Occurs During the Second Phase of Growth of Penicillium chrysogenum?

(a) pH increase

(b) Mycelial mass increases

(c) Both (a) and (b)

(d) Synthesis of penicillin is high

Answer: Both (a) and (b)


30. Streptomycin is Produced by Which of the Following Organisms?

a) Streptomyces noursei

b) Streptomyces nodosus

c) Streptomyces fradiae

d) Streptomyces griseus

Answer: Streptomyces griseus


31. Which of the Following Statements are True about Penicillin at Acidic pH?

a) Penicillin precipitates

b) Penicillin remains in the aqueous phase

c) Penicillin remains in the solvent phase

d) None of the above

Answer: At acidic pH, penicillin remains in the solvent phase.

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FAQs on MCQs on Antibiotics

1. What is the mode of action of antibiotics?

The modes of action of antibiotics can be classified on the basis of the target site and, to some extent, to the alterations in structure produced.It is characterized by their action on the ribosome, resulting in the alteration of protein synthesis. Some antibiotics function by attaching to components involved in DNA or RNA synthesis, interfering with normal cellular processes and, as a result, compromised bacterial proliferation and survival. Quinolones, metronidazole, and rifampin are other examples. Antibiotics disrupt essential processes or structures in the bacterial cell. The bacterium is either killed or its development is slowed as a result of this. Antibiotics are classified as bactericidal or bacteriostatic based on their actions.


2. What is the antibiotic's minimum inhibitory concentration?

The lowest concentration of a substance, generally a medicine, that limits observable development of a bacterium or bacteria is known as the minimum inhibitory concentration (MIC). The MIC is determined by the pathogen, the human person who is being treated (in vivo only), and the antibiotic itself. Micrograms per millilitre (g/mL) or milligrammes per litre (mg/L) are common units of measurement.


  • The medication is bactericidal and has a minimum inhibitory concentration of 1 mg/L. 

  • The medication is bactericidal and has a minimum inhibitory concentration of 2 mg/L. 

  • Antibiotics are antibiotics that kill germs and can heal life-threatening infectious diseases like pneumonia that previously had no effective treatment.

3. What is the classification of antibiotics?

Antibiotics are chemical medicinal medicines of microbial, synthetic, or semi-synthetic origin that prevent the development of other bacteria at low concentrations.

Classification of Antibiotics:

  • On the basis of chemical structure

  • On the basis of origin

  • On the basis of range of activity ( spectrum of activity)

  • On the basis of mode of action

  • On the basis of effects of their activity

  • On the basis of route of administration

Semi-synthetic antibiotics, such as Penicillin V, contain an original chemical molecule from a microorganism but have been further altered. 


Synthetic antibiotics, such as cephalosporins, are made entirely in a laboratory.