Antibiotics: Introduction, History, Mechanism and Applications

Antibiotics are chemical compounds designed to fight bacterial infections. Unlike antiviral medications (which target viruses) or antifungal drugs (which treat fungal infections), antibiotics specifically act against bacteria—unicellular organisms that can reproduce on their own.

1. Antibiotics: Introduction, History, Mechanism and
Applications
learnmicrobiology.com/antibiotics-introduction-history-mechanism-and-applications/
Introduction
Antibiotics are chemical compounds designed to fight bacterial infections. Unlike
antiviral medications (which target viruses) or antifungal drugs (which treat fungal
infections), antibiotics specifically act against bacteria—unicellular organisms that can
reproduce on their own.
Depending on their mechanism of action, antibiotics can either:
Kill bacteria outright (bactericidal), or
Inhibit bacterial growth and reproduction (bacteriostatic).
Antibiotics can be:
Natural – produced by bacteria or fungi to compete with other microbes.
Semisynthetic – modified from natural compounds to improve stability or activity.
Synthetic – completely manufactured in laboratories.
The key advantage of antibiotics is that they exploit biological differences between
bacterial and human cells, allowing them to eliminate infections without severely
harming the host—although side effects sometimes occur.
History of Antibiotics
The story of antibiotics begins with an accident. In 1928, Scottish bacteriologist
Alexander Fleming observed that a mold contaminant, later identified as Penicillium
notatum, inhibited the growth of Staphylococcus bacteria in his petri dish. He named the
active substance penicillin.
However, Fleming’s discovery remained a laboratory curiosity until the 1940s, when
Howard Florey, Ernst Chain, and Norman Heatley developed methods for mass
production. During World War II, penicillin became a miracle cure, saving thousands of
soldiers from infections that once killed more soldiers than bullets.
This success triggered the “Golden Age of Antibiotics” (1940s–1960s), during which
scientists discovered many new antibiotic classes, including:
Streptomycin – the first drug effective against tuberculosis.
Tetracyclines – broad-spectrum antibiotics.
Erythromycin – a macrolide alternative for penicillin-allergic patients.
By the 1970s, antibiotics had become an integral part of modern medicine.
1/11

2. Mechanism of Action of Antibiotics
Antibiotics work by targeting specific bacterial structures or metabolic pathways.
Below are the main categories:
1. Inhibitors of Cell Wall Synthesis
2. Disruptors of the Cell Membrane
3. Protein Synthesis Inhibitors
4. Inhibitors of Nucleic Acid Synthesis
5. Folate Pathway Inhibitors (Antimetabolites)
1. Inhibitors of Cell Wall Synthesis
Method: By blocking crosslinking or precursor transport, these antibiotics kill bacteria and
disrupt the synthesis of the bacterial peptidoglycan cell wall, resulting in cell lysis.
Examples:
Beta-lactams → penicillins, cephalosporins (ceftriaxone, cefotaxime), carbapenems,
monobactams
Glycopeptides → vancomycin
Others → bacitracin
2. Disruptors of the Cell Membrane
Mechanism: The mechanism involves the use of bactericidal compounds to disrupt the
bacterial cell membrane, which increases permeability and results in the release of
essential intracellular components.
Examples:
2/11

3. Polymyxins (effective against Gram-negative bacteria)
Gramicidin, Tyrocidine (Gram-positive bacteria)
3. Protein Synthesis Inhibitors
Mechanism: By targeting the bacterial 30S or 50S ribosomal subunits, these might be
either bactericidal or bacteriostatic.
Examples:
50S inhibitors → erythromycin (macrolide), chloramphenicol, linezolid
(oxazolidinone)
30S inhibitors → tetracyclines, streptomycin, gentamicin, amikacin
4. Inhibitors of Nucleic Acid Synthesis
Mechanism:  Killing bacteria with substances that disrupt DNA transcription or replication.
Examples:
DNA inhibitors → nalidixic acid, ciprofloxacin, norfloxacin, novobiocin
RNA inhibitors → rifampicin
5. Folate Pathway Inhibitors (Antimetabolites)
Mechanism:  These substances are bacteriostatic, preventing vital enzymes in the folic
acid pathway that are necessary for the production of DNA and RNA.
Example:
Sulfonamides: Prevents the conversion of PABA to dihydrofolic acid.
Trimethoprim: Blocks the conversion of dihydrofolate reductase (DHF) to
tetrahydrofolate (THF).
Applications of Antibiotics
1. Antibiotics that kill tumors
Some antibiotics, like actinomycin D and mitomycin C, are used as chemotherapeutic
agents due to their ability to damage DNA in rapidly dividing cancer cells.
2. In Human Medicine
Antibiotics revolutionized healthcare by treating diseases such as pneumonia,
tuberculosis, syphilis, meningitis, and sepsis.
3/11

4. 3. Antibiotics that preserve food
The canning industry uses some antibiotics (such as chlortetracycline), while the
preservation of fish, meat, and poultry makes use of others (such as Pimaricin
nisin).
Governments typically regulate the use of antibiotics in food preservation.
4. Uses of antibiotics in veterinary medicine and animal feed
Up until a while ago, antibiotics (penicillins, tetracyclines, erythromycins) were used
extensively in the production of animal feeds. Due to this indiscriminate usage,
antibiotic resistance has emerged in both humans and animals.
A new class of antibiotics, such enduracidin and tylosin, have been created for use
in animal feed.
In a similar vein, some antibiotics, such as hygromycin B, theostrepton, and
salinomycin, have been created for use only in veterinary medicine.
5. Using antibiotics to manage plant diseases
Several antibiotics have been created in recent years for the sole purpose of treating
plant diseases, such as blasticidin, tetranactin, and polyoxin.
6. The Use of Antibiotics as Tools in Molecular Biology
At the molecular level, some antibiotics are able to target particular biological
processes.
In reality, these antibiotics are useful instruments for learning about the life sciences.
As a result, a few key details about DNA replication, transcription, and translation
have been gleaned from the usage of particular antibiotics.
Examples of Main Antibiotics
1. Penicillins → Penicillin G, Amoxicillin, Ampicillin
2. Cephalosporins → Cefalexin, Ceftriaxone, Cefepime
3. Carbapenems → Imipenem, Meropenem
4. Monobactams → Aztreonam
5. Glycopeptides → Vancomycin, Teicoplanin
6. Aminoglycosides → Streptomycin, Gentamicin, Amikacin
7. Tetracyclines → Doxycycline, Minocycline
8. Macrolides → Erythromycin, Azithromycin
9. Chloramphenicol → Chloramphenicol
10. Lincosamides → Clindamycin
11. Fluoroquinolones → Ciprofloxacin, Levofloxacin
12. Rifamycins → Rifampicin
13. Sulfonamides & Trimethoprim → Co-trimoxazole
14. Polypeptides → Polymyxin B, Colistin
4/11

5. Sources of Antibiotics
Antibiotics are natural, semisynthetic, or synthetic compounds that inhibit or kill bacteria.
Their sources can be grouped into three main categories:
1. Microbial Sources (Natural Antibiotics)
2. Semisynthetic Antibiotics
3. Synthetic Antibiotics
1. Microbial Sources (Natural Antibiotics)
Many antibiotics are produced by microorganisms as part of their survival strategy to
outcompete other microbes.
a) Bacteria
Actinomycetes (especially Streptomyces) → Produce more than 60% of known
antibiotics.
Streptomyces griseus → Streptomycin
Streptomyces venezuelae → Chloramphenicol
Streptomyces aureofaciens → Tetracyclines
Bacillus species
Bacillus subtilis → Bacitracin
Bacillus polymyxa → Polymyxins
b) Fungi
Penicillium notatum → Penicillin
Cephalosporium acremonium → Cephalosporins
2. Semisynthetic Antibiotics
Derived by chemically modifying natural antibiotics to improve stability, spectrum,
or resistance to bacterial enzymes.
Examples:
Amoxicillin & Ampicillin (from Penicillin G)
Methicillin (penicillin derivative resistant to penicillinase)
Cephalexin (from cephalosporins)
3. Synthetic Antibiotics
Entirely manufactured in laboratories using chemical synthesis, not produced by
microbes.
5/11

6. Examples:
Sulfonamides
Fluoroquinolones (Ciprofloxacin, Norfloxacin)
Oxazolidinones (Linezolid)
Antibiotic Resistance: A Global Threat
While antibiotics save millions of lives, misuse and overuse have accelerated the rise of
antimicrobial resistance (AMR). Resistant strains such as MRSA (Methicillin-resistant
Staphylococcus aureus) and multidrug-resistant tuberculosis (MDR-TB) highlight the
urgent need for responsible antibiotic use.
Strategies to combat resistance include:
Limiting unnecessary prescriptions.
Completing full treatment courses.
Developing new antibiotics and alternatives (phage therapy, antimicrobial
peptides, CRISPR-based antimicrobials).
Frequently Asked Questions (FAQ)
Q1. What are antibiotics?
Antibiotics are medications used to treat bacterial infections by killing bacteria or inhibiting
their growth. They are ineffective against viral infections.
6/11

7. Q2. Who discovered antibiotics?
Alexander Fleming discovered penicillin in 1928, later developed into medicine by Florey,
Chain, and Heatley.
Q3. How do antibiotics work?
Antibiotics function by targeting specific bacterial processes or structures, such as cell
wall synthesis or protein production, thereby disrupting the bacteria's ability to survive and
reproduce.
Q4. What are the common side effects of antibiotics?
Common side effects of antibiotics may include nausea, diarrhea, vomiting, and allergic
reactions. It's important to consult a healthcare provider if side effects are severe or
persistent.
Q5. Can antibiotics be used to treat viral infections?
No, antibiotics are not effective against viral infections such as the common cold or flu.
Antiviral medications are required for treating viral illnesses.
Q6. Why is it important to complete a prescribed course of antibiotics?
Completing a prescribed course of antibiotics is crucial to ensure all bacteria are
eliminated, reducing the risk of developing antibiotic resistance and preventing the
infection from returning.
Q7. What should I do if I miss a dose of antibiotics?
If you miss a dose of antibiotics, take it as soon as you remember. If it's close to the time
of your next dose, skip the missed dose and continue with your regular schedule. Do not
double the dose.
Conclusion
Since the invention of penicillin, antibiotics have revolutionized medicine by providing
effective treatment for bacterial infections and saving millions of lives. Their mechanisms
of action are varied, including interfering with metabolic routes, blocking protein or nucleic
acid production, and disrupting cell walls.
In addition to human health, antibiotics have uses in molecular biology, agriculture, food
preservation, and veterinary medicine. Antibiotic misuse and overuse, on the other hand,
have resulted in the development of antibiotic resistance, which poses a significant threat
to public health worldwide.
As a result, even if antibiotics are still one of the most significant medical advances, their
sensible and prudent use is necessary to maintain their efficacy for future generations.
7/11

8. Also Read
HIV and AIDS: Structure, Transmission, Symptoms, Diagnosis and Prevention
Detection of Viruses: Modern Methods, Applications, and Advancements
Single Cell Protein (SCP): Sources, Production, Advantages, Disadvantages &
Applications
Molecular Blotting: Techniques, Uses, and Significance
Microbiology: From Microorganisms to Career Opportunities
Immune System Cells: The Body’s Cellular Defenders
Medical Microbiology Quiz
Basic Microbiology Quiz
Microbiology Notes
Reference and Sources
https://www.sciencenewstoday.org/what-is-an-antibiotic-definition-types-uses-how-
theywork
https://medical-news.org/the-concerning-truth
https://www.biologydiscussion.com/antibiotics/
www.sciencenewstoday.org/what-is-an-antibiotic-definition-types-uses-how-they-
work
www.theportlandclinic.com/antibiotics-side-effects-and-strategies/
https://pmc.ncbi.nlm.nih.gov/articles
https://www.healthline.com/health/missed-antibiotic-dose
clinicalsci.info/antimicrobial-mechanism-of-action/
https://www.britannica.com/science/antibiotic
https://www.msdmanuals.com/…/overview-of-antibiotics
bing.com/videos
https://biologyinsights.com/folate-synthesis
pharmacyfreak.com/mechanism-of-action-of-sulfonamides/
https://iloveveterinary.com/blog/animal
Test Your Knowledge
Medical Microbiology Quiz
Medical Microbiology Quiz is designed to test and enhance your understanding of
microbes that cause human disease. Covering topics like bacterial pathogens, viral
infections, diagnostic techniques, antimicrobial resistance, and host immune responses,
this quiz is ideal for medical, nursing, and life science students preparing for exams or
clinical practice.
Each question is crafted to reflect real-world medical relevance, helping you link
microbiological concepts with disease mechanisms, diagnosis, and treatment.
8/11

9. Strengthen your clinical microbiology foundation — one question at a time.
1 / 30
Which bacterial infection is diagnosed by the Widal test?
2 / 30
What causes pseudomembranous inflammation in diphtheria?
3 / 30
Which of the following causes gas gangrene?
4 / 30
What is the mode of transmission of Leptospira interrogans?
5 / 30
Which of the following organisms is catalase-positive?
6 / 30
Which bacterial structure is responsible for antibiotic resistance transmission?
7 / 30
Which of the following is an opportunistic fungal pathogen?
8 / 30
Which virus causes infectious mononucleosis?
9 / 30
Which test differentiates Staphylococcus aureus from Staphylococcus epidermidis?
10 / 30
Which organism is associated with peptic ulcers?
11 / 30
Which antibody appears first during an acute infection?
12 / 30
What test is used for diagnosis of Streptococcus pyogenes throat infections?
13 / 30
Which is the most common method for sterilizing surgical instruments?
9/11

10. 14 / 30
Which microorganism is the most common cause of urinary tract infections (UTIs)?
15 / 30
What is the purpose of ELISA in microbiology?
16 / 30
Which organism causes rice-water stools?
17 / 30
Which fungus causes meningitis in AIDS patients?
18 / 30
Which helminth causes perianal itching?
19 / 30
Which of the following bacteria is Gram-positive?
20 / 30
Which of these is a nosocomial infection?
21 / 30
Which test is used to detect latent tuberculosis infection?
22 / 30
What causes antibiotic-associated colitis?
23 / 30
Which viral infection can lead to cervical cancer?
24 / 30
What is the main virulence factor of Streptococcus pneumoniae?
25 / 30
What is the causative agent of Q fever?
26 / 30
Which stain is used to identify Mycobacterium tuberculosis?
10/11

11. 27 / 30
What is the major component of bacterial endotoxin?
28 / 30
Which medium is used for culturing Mycobacterium tuberculosis?
29 / 30
Which of the following organisms causes malaria?
30 / 30
What type of virus is Hepatitis B?
Your score is
The average score is 54%
0%
11/11