29 Questions
Which type of antibiotics acts by inhibiting bacterial multiplication?
Bacteriostatic
Which pharmacological feature is characteristic of antibiotics?
Pass through into tissues and body fluids
Which enzyme is responsible for making chains and cross-links in the peptidoglycan structure of the bacterial cell wall?
Transpeptidase
What is the main content of the bacterial cell wall?
Peptidoglycan chain
Which type of antibiotics can act on only a few different pathogens?
Narrow-spectrum drugs
Which antibiotic feature refers to its ability to target specific pathogens without harming the host.
Selective toxicity
Which type of antibiotics can act on many different pathogens?
Broad spectrum drugs
What is the main feature of antibiotics that allows them to target bacteria without harming the host?
Selective toxicity
Which pharmacological feature ensures that antibiotics do not harm the host?
Selective toxicity
Which enzyme is a member of serine proteases and referred to as penicillin binding proteins (PBPs)?
Transpeptidase
Which antibiotic binds irreversibly to the 30S ribosomal subunit and causes misreading of mRNA?
Tetracycline
What is the mechanism of action of polymyxins like Polymyxin B and Polymyxin E (colistin)?
Inhibition of cytoplasmic membrane function
Which antibiotic is primarily used for Gram-negative bacteria and has a severe nephrotoxicity effect if used systemically?
Colistin
What is the primary mode of action of Aminoglycosides like Gentamicin and Tobramycin?
Inhibition of protein synthesis
Which antibiotic binds to the D-Ala-D-Ala chain and prevents the bridging between peptidoglycan chains?
Vancomycin
What is the primary mechanism of action of beta-lactam antibiotics combined with clavulanic acid, sulbactam, or tazobactam?
Inhibition of cell wall synthesis
Which antibiotic is highly effective against staphylococci and is commonly resistant in both hospital and community-acquired isolates?
Methicillin
What is the primary target of cephalosporins like Cefotaxime, Ceftazidime, and Ceftriaxone?
$50S$ ribosome subunit
$Imipenem$, $Doripenem$, $Ertapenem$, and $Meropenem$ have broad-spectrum activity. Which antibiotic class do they belong to?
$Carbapenems$
What is the primary function of Bacitracin when used in the treatment of skin infections caused by Gram-positive bacteria?
Inhibition of cell wall synthesis
Which antibiotic is replaced by cipro, levo, and moxifloxacin (fluoroquinolones)?
Sulfonamids
What is the mechanism of action of fluoroquinolones like cipro, levo, and moxifloxacin?
Prevents the initiation of RNA synthesis
In which condition is cipro, levo, and moxifloxacin used orally for treatment?
Urinary tract infection
What is the mechanism of action of Sulfonamids?
Competes with p-aminobenzoic acid
How do Sulfonamids inhibit the first step of folic acid synthesis?
By inhibiting dihydropteroate synthetase enzyme
What is the mechanism of action of Trimethoprim?
Inhibits dihydrofolate reductase enzyme
Fluoroquinolones like cipro, levo, and moxifloxacin are ineffective against aerobic and facultative anaerobic bacteria.
False
Sulfonamids work by breaking down bacterial DNA.
False
Trimethoprim prevents the formation of tetrahydrofolic acid from dihydrofolic acid by inhibiting the dihydrofolate reductase enzyme.
True
Study Notes
Inhibitors of Bacterial Cell Wall
- Inhibit the last step of peptidoglycan synthesis (transpeptidation reaction)
- Examples:
- Clavulanic acid
- Sulbactam
- Tazobactam
- They act by inhibiting the β-lactamase enzyme, which breaks the β-lactam ring
Beta-Lactam Antibiotics
- Combined use with β-lactamase inhibitors
- Examples:
- Penicillins
- Cephalosporins
- Cephamycins
Penicillins
- Natural penicillins:
- Penicillin G: inactivated by stomach acid, IV use possible for limited susceptible bacteria
- Penicillin V: acid-resistant, oral form can be used
- Penicillinase-resistant penicillins:
- Methicillin
- Oxacillin
- Cloxacillin
- Dicloxacillin
- Similar to natural penicillins, highly effective against staphylococci
- Methicillin-resistant isolates are common in both hospital and community-acquired (MRSA)
Aminopenicillins
- Broad-spectrum penicillins
- Examples:
- Ampicillin
- Amoxicillin
Other Penicillins
- Carbenicillin
- Ticarcillin
- Piperacillin
- Broader spectrum of action, including Gram-negative bacteria (Klebsiella, Enterobacter, and Pseudomonas species)
Cephalosporins and Cephamycins
- First isolated from Cephalosporium mold
- Cephamycins are similar to cephalosporins but more resistant to β-lactamase hydrolysis
- Examples:
- 1st Generation Cephalosporins:
- Cephalexin
- Cephalothin
- Cefazolin
- Cefapirin
- Cefradin
- 2nd Generation Cephalosporins:
- Increased Gram-negative activity
- Cefochlor
- Cefuroxime
- 3rd Generation Cephalosporins:
- More resistant to β-lactamases
- Cefoxitin
- Cefotetan
- 4th Generation Cephalosporins:
- Pass through the outer membrane of Gram-negative bacteria easier and faster
- Cefotaxime
- Ceftazidime
- Ceftriaxone
- Cefixime
- 5th Generation Cephalosporins:
- Increased Gram-negative activity
- Cefepime
- Cefpirom
- 1st Generation Cephalosporins:
Carbapenems
- Examples:
- Imipenem
- Doripenem
- Ertapenem
- Meropenem
- Frequently prescribed, broad-spectrum
Monobactams
- Narrow-spectrum drugs, only aerobic Gram-negative activity
- Example:
- Aztreonam
Inhibitors of Bacterial Cell Wall
- Vancomycin
- Teicoplanin
- Ineffective against Gram-negative bacteria
- Bind to D-Ala-D-Ala chain, preventing bridging between peptidoglycan chains
- Bactericidal effect
Polypeptides
- Bacitracin
- Isoniazid
- Ethionamide
- Ethambutol
- Cycloserine
- Cell wall-effective antibiotics used in the treatment of Mycobacteria sp.
Inhibitors of Cytoplasmic Membrane Function
- Polymyxins (A, B, C, D, E)
- Obtained from Bacillus polymyxa
- Act as a detergent, binding to the outer membrane, increasing cell permeability, and causing cell death
- Polymyxin B and E (colistin) have severe nephrotoxicity, used systemically in isolates sensitive to only colistin (e.g., Acinetobacter and Pseudomonas)
Daptomycin
- Effective against Gram-positive bacteria
- Cannot pass through the Gram-negative cell wall and reach the cytoplasmic membrane
- Binds irreversibly to the cytoplasmic membrane, causing disruption in depolarization and ion exchange, leading to cell death
- Used against Staphylococci, Streptococci, and Vancomycin-resistant Enterococci (VRE)
Protein Synthesis Inhibition
- Aminoglycosides (bactericidal)
- Tetracyclines (bacteriostatic)
- Glycylcyclines (bacteriostatic)
- Aminoglycosides:
- Streptomycin
- Neomycin
- Kanamycin
- Tobramycin
- Gentamicin
- Sisomycin
- All bind irreversibly to the 30S ribosomal subunit, causing misreading of mRNA and early separation of mRNA from the ribosome
Tetracyclines
- Bacteriostatic
- Reversible attachment to 30S, inhibiting aminoacyl-tRNA binding to the 30S ribosome-mRNA complex
- Examples:
- Tetracycline
- Doxycycline
- Minocycline
Macrolides
- Erythromycin
- Modifications:
- Azithromycin
- Clarithromycin
- Roxithromycin
- Binds reversibly to the 50S ribosomal subunit, blocking polypeptide elongation
Quinolones
- Examples:
- Nalidixic acid
- Ciprofloxacin
- Levofloxacin
- Moxifloxacin
- Inhibit DNA topoisomerase type II (DNA gyrase) or type IV enzymes necessary for DNA replication, recombination, and DNA repair
Antimicrobic Features
- Selective toxicity
- Broad-spectrum effect
- Bacteriosidal effect
- Pharmacological features:
- Not toxic to the host
- Pass through into tissues and body fluids
Test your knowledge about antibiotics and antimicrobics used in the treatment of infectious diseases. Learn about the pharmacological features, types, and effects of antibiotics in this quiz.
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