*Antibiotics - Full Long Explanation* 💊
*Antibiotic* = "Anti = against, Bios = life". Drugs that kill bacteria or stop their
growth. They DO NOT work on viruses like flu, COVID, common cold.
Discovered by Alexander Fleming in 1928 = *Penicillin* from _Penicillium_
fungus. Called "miracle drugs" of 20th century.
*1. How Antibiotics Work - 5 Main Mechanisms*
Antibiotics target parts of bacteria that human cells don’t have. That’s why they
don’t kill us.
Mechanism Target in Bacteria Example Drugs What Happens
**1. Cell wall synthesis** Peptidoglycan cell wall **Penicillin, Amoxicillin,
Cephalosporins** Wall becomes weak → bacteria burst due to osmosis
**2. Protein synthesis** 70S ribosomes of bacteria **Tetracycline,
Erythromycin, Streptomycin** Bacteria can’t make proteins → die
**3. DNA replication** DNA gyrase/topoisomerase **Ciprofloxacin,
Levofloxacin** DNA can’t copy → cell can’t divide
**4. Metabolic pathway** Folic acid synthesis **Sulfonamides,
Cotrimoxazole** Blocks vitamin production → bacteria starve
**5. Cell membrane** Membrane permeability **Polymyxin B** Puts holes in
membrane → contents leak out
*Key*: Human cells have 80S ribosomes + no cell wall + make folic acid from
food. So antibiotics are "selectively toxic" to bacteria.
*2. 2 Types Based on Action*
1. *Bactericidal* = Kill bacteria directly. "Cidal = killing"
Ex: Penicillin, Ciprofloxacin, Aminoglycosides. Used in severe infections like
meningitis, sepsis.
2. *Bacteriostatic* = Stop bacteria from growing/multiplying. Body’s immune
system kills them. "Static = stop"
Ex: Tetracycline, Erythromycin, Sulfonamides. Used in mild infections like acne,
chest infection.
*3. 6 Major Classes of Antibiotics*
Class Common Names Targets Used For
**1. Penicillins** Penicillin G, Amoxicillin, Ampicillin Cell wall Throat infection,
pneumonia, UTIs
**2. Cephalosporins** Ceftriaxone, Cefixime Cell wall Typhoid, meningitis,
surgery prevention
**3. Aminoglycosides** Gentamicin, Streptomycin 70S ribosomes TB, sepsis.
Toxic to kidney/ear
**4. Tetracyclines** Doxycycline, Tetracycline 70S ribosomes Acne, cholera,
*Antibiotic* = "Anti = against, Bios = life". Drugs that kill bacteria or stop their
growth. They DO NOT work on viruses like flu, COVID, common cold.
Discovered by Alexander Fleming in 1928 = *Penicillin* from _Penicillium_
fungus. Called "miracle drugs" of 20th century.
*1. How Antibiotics Work - 5 Main Mechanisms*
Antibiotics target parts of bacteria that human cells don’t have. That’s why they
don’t kill us.
Mechanism Target in Bacteria Example Drugs What Happens
**1. Cell wall synthesis** Peptidoglycan cell wall **Penicillin, Amoxicillin,
Cephalosporins** Wall becomes weak → bacteria burst due to osmosis
**2. Protein synthesis** 70S ribosomes of bacteria **Tetracycline,
Erythromycin, Streptomycin** Bacteria can’t make proteins → die
**3. DNA replication** DNA gyrase/topoisomerase **Ciprofloxacin,
Levofloxacin** DNA can’t copy → cell can’t divide
**4. Metabolic pathway** Folic acid synthesis **Sulfonamides,
Cotrimoxazole** Blocks vitamin production → bacteria starve
**5. Cell membrane** Membrane permeability **Polymyxin B** Puts holes in
membrane → contents leak out
*Key*: Human cells have 80S ribosomes + no cell wall + make folic acid from
food. So antibiotics are "selectively toxic" to bacteria.
*2. 2 Types Based on Action*
1. *Bactericidal* = Kill bacteria directly. "Cidal = killing"
Ex: Penicillin, Ciprofloxacin, Aminoglycosides. Used in severe infections like
meningitis, sepsis.
2. *Bacteriostatic* = Stop bacteria from growing/multiplying. Body’s immune
system kills them. "Static = stop"
Ex: Tetracycline, Erythromycin, Sulfonamides. Used in mild infections like acne,
chest infection.
*3. 6 Major Classes of Antibiotics*
Class Common Names Targets Used For
**1. Penicillins** Penicillin G, Amoxicillin, Ampicillin Cell wall Throat infection,
pneumonia, UTIs
**2. Cephalosporins** Ceftriaxone, Cefixime Cell wall Typhoid, meningitis,
surgery prevention
**3. Aminoglycosides** Gentamicin, Streptomycin 70S ribosomes TB, sepsis.
Toxic to kidney/ear
**4. Tetracyclines** Doxycycline, Tetracycline 70S ribosomes Acne, cholera,
