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Antibiotic Definition - Types & Side Effects

Antibiotic Definition - Types & Side Effects

Edited By Irshad Anwar | Updated on Jul 02, 2025 05:22 PM IST

Antibiotics are drugs synthesized from other organisms (for example, moulds, fungi, and some soil bacteria) to help fight harmful microorganisms. However, they are not very useful against some microbes, including viruses. Antibiotics are made on a very large scale with the help of the fermentation process. A large tank is made available with the growth medium that secretes nutrition for the microorganism’s growth. Regulation of temperature, pH levels, oxygen levels, and nutrient parameters in the fermentation tank is the most important step in producing antibiotics. Antibiotics are one of the important topics in biology which comes under chapter microbes in human welfare class 12th. The topic carries weightage of 5 to 6% of total marks in NEET, Paramedical or Pharmacy entrance exams.

This Story also Contains
  1. Antibiotic Definition
  2. History Of Antibiotic Production
  3. Different Types Of Antibiotics
  4. Mechanism Of Action Of Antibiotics
  5. Side Effects Of Antibiotics
  6. Tips, Tricks, And Strategies To Prepare For Antibiotics
  7. Types Of Questions Asked On Antibiotics
  8. Weightage Of Antibiotics In Different Entrance Exams
  9. Recommended Video

Also Read

Antibiotic Definition

Antibiotics are defined as the chemical compounds that are responsible for killing or stopping the growth of bacteria. Truly speaking, antibiotics are defined as a further class of organic anti-infective agents that are usually produced from bacteria or moulds that are toxic to many other bacteria and can kill them. However the term "antibiotic" is now used in an easy way to refer to anti-infectives produced from synthetic and semisynthetic compounds.

History Of Antibiotic Production

Going back to 1928, Scottish bacteriologist Alexander Fleming saw some colonies of bacteria that were growing on a culture plate, and these colonies had been affected by a mould species. Some more important events related to the antibiotic invention and its production are discussed below:

  • Another biochemist Ernst Chain, Australian Pathologist Howard Florey, and other scientists later on invented that isolated active ingredient that was responsible for killing the bacteria. They named it penicillium.

  • The penicillium species were formed on the contaminated bacterial culture and it killed the bacteria which were surrounding it.

  • Later on, penicillium was one of the most effective tools against some of the serious bacterial infections.

  • There are different types of penicillin available today to treat different bacterial infections.

  • By the 1950s there had been several chemical modifications made to the penicillin molecule which led to the formation of semisynthetic penicillin.

Different Types Of Antibiotics

There have been several modifications made to penicillin since it was developed. Several forms of antibiotics were formed to fight several diseases which are based on bacterial infections. Some of the major antibiotics and their backgrounds and treatments are discussed below:

TypeKey FeaturesCommon UsesBackground
PenicillinsFirst discovered antibiotics; effective against many bacteria.Sore throat, skin infections, respiratory issues.Discovered by Alexander Fleming; works by disrupting bacterial cell walls.
TetracyclinesBroad-spectrum; inhibits protein synthesis; photosensitive.Acne, UTIs, STDs, eye infections.Effective against a wide range of bacteria; not recommended for young children due to dental effects.
CephalosporinsSimilar to penicillins; effective against gram-negative bacteria.Ear infections, UTIs, lung infections.Used for patients allergic to penicillin; kills bacteria effectively.
MacrolidesGood for respiratory and skin infections; inhibits protein synthesis.Pneumonia, whooping cough, skin infections.Alternative for those allergic to penicillins; effective against community-acquired infections.
SulfonamidesWorks against both gram-positive and gram-negative bacteria; inhibits folic acid production.UTIs, pneumonia, ear infections.Can cause allergic reactions and kidney stones with long-term use.
GlycopeptidesTargets serious infections from gram-positive bacteria like MRSA.MRSA infections, endocarditis, C. difficile.Inhibits cell wall formation; Vancomycin is a key example; may cause red man syndrome with prolonged use.


Mechanism Of Action Of Antibiotics

The table mentioned below contains all the steps which are involved in the mechanism of antibiotics.

Process

Stages

Target recognition

  • The antibiotics enter the bacterial cell and recognise a specific target that can be either cell wall, ribosome, DNA or some kind of metabolic enzyme.

Binds to the Target

  • After recognising the target the antibiotic attaches itself to the target.

  • These targets can be of different chemical formulations such as cell wall replication enzymes, folic acid synthesis enzymes and sometimes even the DNA.

Growth/inhibition or Death

  • In this stage, the antibiotic directly kills the bacteria. These are also known as Bactericidal Antibiotics.


  • There are also antibiotics which are bacteriostatic which means they inhibit bacterial growth.

  • Attack on the immune system to eliminate the bacteria. (e.g: tetracyclines)

Elimination of the bacteria

  • After the bacteria has been killed our immune system discards the dead bacteria.

  • This helps in saving the immune system and body from severe bacterial disease.


Side Effects Of Antibiotics

Regular use of antibiotics can lead to certain side effects which can be serious. Antibiotics with their side effects are mentioned in the table below:

Type of antibiotic

Common side effects after long-term use

All Antibiotics

Diarrhea, nausea, vomiting and rashes

Tetracyclines

Photosensitivity ( redness in the sunlight)

Fluoroquinolone

Muscle and skeletal tissue pains.

Lower Spine region pain.

Macrolides

Ear problems ( loss of hearing)

Penicillin

Low white blood cell count.

Sulfonamides

Kidney stones formation.


Tips, Tricks, And Strategies To Prepare For Antibiotics

It's hard to remember everything in a single go. We made the entire problem easy. Some of the tricks regarding antibiotics are given below which you can use to memorize the important points.

ANTIBIOTICS: Important Points

  • A: Antimicrobial

  • N: Not for Viruses

  • T: treatment for Bacterial Infections

  • I: inhibits the growth of Bacteria

  • B: works against Bacterial Resistance

  • O: oral / IV use

  • T: Test for Effectiveness

  • I: interactions

  • C: Common side effects are nausea, diarrhoea and allergic reactions.

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Classification of Antibiotics

  • P: Penicillin

  • C: cephalosporins

  • T: tetracycline

  • M: Macrolides

  • S: Sulfonamides

Side effects mnemonics

  • N: Nausea

  • D: Diarrhea

  • A: Allergic reactions

  • H: Hearing Loss

  • K: Kidney Stones

Types Of Questions Asked On Antibiotics

During the preparation of the exam, there are different types of questions asked about Antibiotics in different forms. The table given below contains the different patterns of questions asked in different exams.

Exam type

Types of questions asked

CBSE

  • Definition of Antibiotics and its types.

  • Benefits.

  • Uses of Antibiotics.

  • Side effects of Antibiotics.

NEET

  • Mechanism of Action of Antibiotics.

  • Use of Antibiotics in Treatments.

  • Different types of antibiotics.

  • Use of different types of antibiotics.

Paramedical

  • Medications based on antibiotics.

  • Types of antibiotics.

  • Side effects of antibiotics.

  • Treatment of side effects of antibiotics.


Weightage Of Antibiotics In Different Entrance Exams

It is important to keep weightage of the topic in mind throughout the preparation. The weightage of antibiotics in different exams is mentioned below in the table:

Exam

Weightage

CBSE

5%

NEET

7%

Paramedical

4%

Pharmacy

6%


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Frequently Asked Questions (FAQs)

1. What are the different types of penicillin?

There are usually two different types of penicillin.

Penicillin VK: It is responsible for fighting against bacterial infections. Examples include ear infections.

Penicillin G is effective against both gram-positive and gram-negative Cocci bacterial infections.Examples of this include susceptible bacterial infections in the stomach.

2. What are the different types of antimicrobial therapies available now?

There are two different types of antimicrobial therapies that are available:

 Microbicidal therapy is  responsible for killing microorganisms.

Microbiostatic therapy is only used to prevent microbial growth and does not kill microorganisms.

3. What is the difference between immunosuppressants and antibiotics?

Immunosuppressants are defined as any agent in a class of drugs that is responsible for inhibiting the immune system. Immunosuppressants are helpful to prevent the rejection of an organ after the process of transplantation and in the treatment of autoimmune diseases.

 Antibiotics are defined as the chemical compounds that are responsible for killing or stopping the growth of bacteria.

4. Name the organism against which antibiotics are not effective.

Antibiotics are not effective against viruses. These are acellular organisms that do not exist outside of the human body but multiply within it.They multiply so rapidly that antibiotics are not effective against viruses.

5. Name a broad-spectrum antibiotic.

Tetracyclines are defined as broad-spectrum antibiotics that are effective against many bacteria.

6. What is the definition of antibiotics?

Antibiotics are antimicrobial agents that are used to kill bacteria and treat bacterial infections.  

7. What is an antibiotic's simple definition?

Antibiotics are simple medications that help treat bacterial infections by preventing their growth

8. What are antibiotics with an example?

Antibiotics are simple drops that are used to fight back serious infections such as penicillin is the most common antibiotic used against pneumonia.  

9. What is the difference between broad-spectrum and narrow-spectrum antibiotics?
Broad-spectrum antibiotics are effective against a wide range of bacterial species, while narrow-spectrum antibiotics target specific types of bacteria. Broad-spectrum antibiotics are often used when the exact pathogen is unknown, but they can also disrupt beneficial bacteria in the body. Narrow-spectrum antibiotics are more targeted but require accurate diagnosis of the infection.
10. What is the difference between bactericidal and bacteriostatic antibiotics?
Bactericidal antibiotics kill bacteria directly, while bacteriostatic antibiotics inhibit bacterial growth without necessarily killing them. Bactericidal antibiotics (like penicillins) are often preferred for severe infections or in immunocompromised patients, while bacteriostatic antibiotics (like tetracyclines) may be used for less severe infections.
11. How do tetracycline antibiotics work and what are their unique properties?
Tetracyclines work by binding to bacterial ribosomes and inhibiting protein synthesis. They are broad-spectrum antibiotics effective against many bacteria, some protozoa, and even some viruses. Tetracyclines have the unique property of being able to accumulate in bones and teeth, which is why they're not typically given to children or pregnant women.
12. How do aminoglycoside antibiotics work and what are their potential side effects?
Aminoglycosides work by binding to bacterial ribosomes and interfering with protein synthesis. They are bactericidal and effective against many gram-negative bacteria. However, they can have serious side effects, including kidney damage (nephrotoxicity) and hearing loss (ototoxicity), so their use is carefully monitored.
13. What is the "ESKAPE" group of pathogens and why are they significant?
ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are a group of bacteria known for their ability to "escape" the effects of antibiotics through various resistance mechanisms. They are significant because they represent some of the most challenging antibiotic-resistant infections in clinical settings.
14. What are antibiotics and how do they work?
Antibiotics are substances that kill or inhibit the growth of bacteria. They work by targeting specific structures or processes in bacterial cells, such as cell walls, protein synthesis, or DNA replication. Antibiotics are ineffective against viruses, fungi, or other non-bacterial pathogens.
15. How do antibiotics distinguish between human cells and bacterial cells?
Antibiotics target structures or processes that are unique to bacterial cells or are significantly different from those in human cells. For example, many antibiotics target bacterial cell walls, which human cells don't have. This selectivity allows antibiotics to kill bacteria without harming human cells.
16. How do beta-lactam antibiotics work?
Beta-lactam antibiotics, which include penicillins and cephalosporins, work by interfering with bacterial cell wall synthesis. They contain a beta-lactam ring that binds to and inhibits enzymes needed for cell wall formation, causing the bacteria to burst and die.
17. How do macrolide antibiotics differ from beta-lactams in their mechanism of action?
While beta-lactams target cell wall synthesis, macrolide antibiotics (like erythromycin) inhibit protein synthesis in bacteria. They bind to the bacterial ribosome, preventing the addition of new amino acids to growing peptide chains, thus stopping bacterial growth.
18. What is the "minimum inhibitory concentration" (MIC) in antibiotic therapy?
The minimum inhibitory concentration (MIC) is the lowest concentration of an antibiotic that prevents visible growth of a bacterium. It's used to determine the effectiveness of an antibiotic against a specific bacterial strain and to guide dosing in clinical settings.
19. What are some common side effects of antibiotics?
Common side effects of antibiotics include digestive issues (nausea, diarrhea, stomach pain), fungal infections (like yeast infections), and allergic reactions. Some antibiotics can also cause more serious side effects like liver damage or blood disorders, though these are less common.
20. How do antibiotics affect the human microbiome?
Antibiotics can significantly disrupt the human microbiome by killing both harmful and beneficial bacteria. This disruption can lead to short-term side effects like diarrhea and potentially contribute to longer-term health issues. The microbiome usually recovers over time, but repeated antibiotic use can lead to lasting changes.
21. What is antibiotic-associated diarrhea and why does it occur?
Antibiotic-associated diarrhea occurs when antibiotics disrupt the normal balance of gut bacteria. This can allow harmful bacteria like C. difficile to overgrow or cause changes in metabolism of carbohydrates, leading to diarrhea. It's a common side effect of antibiotic use, especially with broad-spectrum antibiotics.
22. Why are antibiotics considered a "double-edged sword" in medicine?
Antibiotics are considered a double-edged sword because while they are effective in treating bacterial infections, their overuse or misuse can lead to antibiotic resistance. This means bacteria evolve to become immune to the effects of antibiotics, making infections harder to treat and potentially creating "superbugs."
23. How do fluoroquinolone antibiotics work?
Fluoroquinolones work by inhibiting bacterial DNA gyrase and topoisomerase IV, enzymes essential for DNA replication. This prevents the bacteria from reproducing, effectively killing them. However, fluoroquinolones can have serious side effects and are often reserved for more severe infections.
24. How do probiotics relate to antibiotic use?
Probiotics are beneficial bacteria that can help restore the balance of gut microbiota disrupted by antibiotics. Taking probiotics during or after antibiotic treatment may help reduce side effects like diarrhea and prevent opportunistic infections like C. difficile.
25. What is the concept of "antibiotic cycling" in hospitals?
Antibiotic cycling is a strategy where different classes of antibiotics are rotated in a healthcare setting over time. The goal is to reduce selective pressure on bacteria and slow the development of resistance. However, its effectiveness in practice is debated, as resistance genes can persist in bacterial populations.
26. What is the concept of "persister cells" in bacterial populations?
Persister cells are a small subset of bacterial cells that enter a dormant, non-dividing state, making them highly tolerant to antibiotics. Unlike resistant cells, persisters don't have genetic changes; their tolerance is due to their metabolic state. They can survive antibiotic treatment and later "wake up" to repopulate, contributing to recurrent infections.
27. What is the role of plasmids in antibiotic resistance?
Plasmids are small, circular DNA molecules that can replicate independently of chromosomal DNA. They often carry antibiotic resistance genes and can be easily transferred between bacteria, even of different species. This horizontal gene transfer via plasmids is a major mechanism for the spread of antibiotic resistance.
28. How do antibiotics impact the risk of fungal infections?
Antibiotics can increase the risk of fungal infections, particularly yeast infections, by disrupting the normal balance of microorganisms in the body. When bacteria are killed off by antibiotics, it can create an opportunity for fungi, which are not affected by antibiotics, to overgrow and cause infection.
29. What are the challenges in developing new antibiotics?
Developing new antibiotics faces several challenges: high research and development costs, low return on investment due to controlled use of new antibiotics, difficulty in finding new mechanisms of action, and regulatory hurdles. Additionally, bacteria can quickly develop resistance to new antibiotics, shortening their effective lifespan.
30. What is antibiotic cross-resistance and why is it a concern?
Antibiotic cross-resistance occurs when bacteria resistant to one antibiotic are also resistant to other antibiotics, often with similar structures or mechanisms of action. It's a concern because it limits treatment options and can lead to the rapid spread of multi-drug resistant bacteria.
31. How do antibiotics impact horizontal gene transfer in bacteria?
Antibiotics can stimulate horizontal gene transfer (HGT) between bacteria. HGT is a process where genetic material is transferred between organisms in ways other than traditional reproduction. Antibiotics can induce stress responses in bacteria that increase HGT, potentially spreading antibiotic resistance genes.
32. How do biofilms contribute to antibiotic resistance?
Biofilms are communities of microorganisms that adhere to surfaces and secrete a protective extracellular matrix. This matrix can prevent antibiotics from reaching the bacteria, while the altered metabolic state of bacteria in biofilms can make them less susceptible to antibiotics. Biofilms are a major factor in chronic and device-associated infections.
33. What is the "post-antibiotic effect" and why is it important in dosing?
The post-antibiotic effect refers to the continued suppression of bacterial growth after antibiotic concentrations have fallen below the minimum inhibitory concentration. This effect varies among antibiotics and is important in determining dosing intervals, as it allows for less frequent dosing of some antibiotics while maintaining effectiveness.
34. What is antibiotic resistance and how does it develop?
Antibiotic resistance occurs when bacteria evolve to survive exposure to antibiotics. It develops through natural selection: bacteria with genetic mutations that allow them to survive antibiotics reproduce, passing on their resistance genes. Overuse and misuse of antibiotics accelerate this process by creating more opportunities for resistant bacteria to thrive.
35. Can antibiotics treat viral infections like the common cold or flu?
No, antibiotics are not effective against viral infections like the common cold or flu. Antibiotics specifically target bacteria and have no effect on viruses. Using antibiotics for viral infections is ineffective and can contribute to antibiotic resistance.
36. What is antibiotic stewardship and why is it important?
Antibiotic stewardship refers to coordinated programs and interventions designed to improve and measure the appropriate use of antibiotics. It's important because it helps preserve the effectiveness of antibiotics, reduces adverse events, and combats the spread of antibiotic-resistant bacteria.
37. What is antibiotic prophylaxis and when is it used?
Antibiotic prophylaxis is the preventive use of antibiotics before potential exposure to harmful bacteria. It's commonly used before certain surgical procedures, in immunocompromised patients, or after exposure to certain infectious diseases. However, it must be used judiciously to prevent contributing to antibiotic resistance.
38. What is the role of efflux pumps in antibiotic resistance?
Efflux pumps are protein structures in bacterial cell membranes that can expel antibiotics from the cell. Some bacteria develop increased expression of these pumps as a mechanism of antibiotic resistance, effectively reducing the concentration of antibiotics inside the cell to non-lethal levels.
39. How do antibiotics affect the development of the immune system in children?
Early and frequent exposure to antibiotics in children may alter the development of their microbiome, which plays a crucial role in immune system development. This disruption has been associated with increased risks of allergies, asthma, and other immune-mediated disorders later in life.
40. How do antibiotics interact with the immune system?
Antibiotics can have complex interactions with the immune system. While they primarily work by directly killing or inhibiting bacteria, some antibiotics also have immunomodulatory effects. For example, macrolides can reduce inflammation, while some antibiotics may temporarily suppress certain immune functions.
41. How do antibiotics affect gut-brain communication?
Antibiotics can disrupt the gut microbiome, which plays a crucial role in gut-brain communication. This disruption can potentially affect mood, behavior, and cognitive function. Research suggests that antibiotic use, especially in early life, may be associated with neurodevelopmental and mental health outcomes.
42. How do antibiotics affect bacterial evolution?
Antibiotics exert strong selective pressure on bacterial populations, favoring the survival and reproduction of resistant individuals. This can lead to rapid evolution of resistance mechanisms. Additionally, antibiotics can increase mutation rates in bacteria through stress responses, potentially accelerating evolution.
43. What is the "mutant selection window" in antibiotic therapy?
The mutant selection window is the range of antibiotic concentrations between the minimum inhibitory concentration (MIC) and the mutant prevention concentration (MPC). Within this window, antibiotic-resistant mutants can be selectively amplified. Proper dosing aims to minimize time in this window to reduce the development of resistance.
44. How do sulfonamide antibiotics work and what are their limitations?
Sulfonamides work by inhibiting bacterial folate synthesis, which is necessary for DNA replication. They compete with para-aminobenzoic acid (PABA), a substrate in the folate synthesis pathway. While effective against many bacteria, resistance to sulfonamides is common, and they can cause allergic reactions in some patients.
45. What is the role of bacteriophages in antibiotic resistance?
Bacteriophages (viruses that infect bacteria) can contribute to antibiotic resistance by transferring resistance genes between bacteria through transduction. However, phages are also being researched as potential alternatives to antibiotics, as they can be used to specifically target and kill bacteria without affecting other microorganisms.
46. How do antibiotics affect wound healing?
While antibiotics can prevent or treat infections in wounds, they can also impact the wound healing process. Some antibiotics may slow wound healing by interfering with cell proliferation or collagen synthesis. Additionally, disruption of the normal microbiome on the skin can affect the wound healing environment.
47. What is the concept of "collateral sensitivity" in antibiotic resistance?
Collateral sensitivity occurs when bacteria that develop resistance to one antibiotic become more susceptible to another. This phenomenon is being studied as a potential strategy to combat antibiotic resistance, as it suggests that carefully designed antibiotic cycling or combination therapies could exploit these trade-offs in resistance.
48. How do antibiotics impact the development of the gut-associated lymphoid tissue (GALT)?
Antibiotics, especially when given early in life, can disrupt the normal development of gut-associated lymphoid tissue (GALT), a crucial part of the immune system. This disruption can alter immune responses and potentially increase susceptibility to certain diseases later in life, highlighting the importance of judicious antibiotic use in infants and children.
49. What is the "inoculum effect" in antibiotic therapy?
The inoculum effect refers to the phenomenon where the effectiveness of an antibiotic decreases as the initial bacterial density increases. This effect is particularly relevant for some beta-lactam antibiotics and can impact the choice of antibiotic and dosing strategies in severe infections with high bacterial loads.
50. How do antibiotics affect bacterial communication (quorum sensing)?
Some antibiotics can interfere with quorum sensing, the process by which bacteria communicate and coordinate their behavior. This interference can affect bacterial virulence, biofilm formation, and other group behaviors. Understanding these effects could lead to new strategies for combating bacterial infections.
51. What is the role of efflux pump inhibitors in combating antibiotic resistance?
Efflux pump inhibitors are compounds that block bacterial efflux pumps, which are a major mechanism of antibiotic resistance. By inhibiting these pumps, they can increase the intracellular concentration of antibiotics, potentially restoring the effectiveness of antibiotics against resistant bacteria. They are being researched as potential adjuvants to antibiotic therapy.
52. How do antibiotics impact the metabolism of other drugs?
Some antibiotics can affect the metabolism of other drugs by interacting with liver enzymes, particularly cytochrome P450 enzymes. This can lead to increased or decreased levels of other medications, potentially causing adverse effects or reduced efficacy. For example, erythromycin can inhibit the metabolism of certain statins, increasing their concentration in the blood.
53. What is the concept of "antibiotic tolerance" and how does it differ from resistance?
Antibiotic tolerance refers to the ability of bacteria to survive exposure to antibiotics without having specific resistance mechanisms. Tolerant bacteria are not killed by antibiotics but merely stop growing in their presence. This differs from resistance, where bacteria can grow and multiply in the presence of antibiotics. Tolerance can lead to persistent infections that are difficult to treat.
54. How do antibiotics affect the production of bacterial toxins?
Antibiotics can sometimes paradoxically increase the production of bacterial toxins. For example, some antibiotics that disrupt cell wall synthesis in certain bacteria can trigger increased toxin release. This effect, known as antibiotic-induced toxin release, is particularly relevant for infections caused by toxin-producing bacteria like Clostridium difficile.
55. What is the "Eagle effect" in antibiotic therapy?
The Eagle effect, also known as the paradoxical effect, is a phenomenon where higher concentrations of certain antibiotics (particularly beta-lactams) can be less effective at killing bacteria than lower concentrations. This counterintuitive effect is thought to occur due to rapid lysis of bacteria at high antibiotic concentrations

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