1. Antibiotics: Classification and Mechanisms of Action
A/Prof Olga Perovic, Principal Pathologist, Center for Healthcare Associated Infections Antimicrobial Resistance and Mycoses, National Institute for Communicable Diseases at NHLS and Associate Professor at WITS
Date: 2/4/2019
WHO GLASS training workshop on AMR

2. Objectives To explain general principles of antibiotics
To classify antibiotics
To describe and understand mechanisms of action of antibiotics.

3. What are antibiotics by definition?
Antibiotics are substances produced by microorganisms which are antagonistic (opposed) to the growth or life of others bacteria.
Difference between human (eukaryotic) and bacterial (prokaryotic) cell structure allow antibiotics to target bacterial structures but not host cell function-this phenomenon is called as selective toxicity
Bactericidal (killing) and bacteriostatic (growth inhibition)
No harm to patient.
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4. Evolution of antibiotics
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5. Climate and Culture Survey Embracing Diversity, Building Unity
When to use them?
Is antibiotics treatment indicated based on clinical findings?
Evident bacterial infection
Localized infections: pneumonia, pyelonephritis etc.
Infections with characteristic clinical findings: cellulitis, bacterial arthritis.
Inflammatory markers: leukocytosis, neutrophilia, lymphocytopenia, left shift, presence of bands, elevated C-reactive protein (CRP) and procalcitonin (PCT).
2. What is emergency of the patients condition
Non-critical conditions: mild infection, which does not require treatment until the diagnosis is not established
Critical conditions: the patient with suspected severe infection:
Febrile neutropenia
Bacterial meningitis
Necrotizing cellulitis
Severe sepsis and septic shock
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6. Role of the diagnostic stewardship
Have appropriate clinical specimens been obtained, examined and cultured?
MC&S Microscopy Gram stain; Culture - anaerobic and aerobic cultures; Latex agglutination
Antibiotic Susceptibility Testing (AST)-Empirical antibiotic treatment must be modified when the AST becomes available.
In consultation with microbiologist , additional tests such as antibiotic minimum inhibitory concentration (MIC), antibiotic assay, serum bactericidal activity and synergy tests of antibiotic combinations may be useful in serious infections (e.g. endocarditis and in immunocompromised patients). In vitro resistance generally predicts clinical ineffectiveness but not always. The pharmacokinetics and pharmacodynamics (e.g. penetration into relevant tissues) as well as the spectrum of activity of the antibiotic must be considered. Antibiotic pharmacokinetic principles should determine the dosage and frequency of antibiotic regimens.
2. Which organisms are most likely to be causing the infection?
Type of focal infection
Age: bacterial meningitis of newborns – group B streptococci, Gram-negative bacteria
Epidemiologic features: hospital vs. community acquired infections, prior antibiotic use, etc.
3. If multiple antibiotics are available to treat pathogen, which agent would be the best?
Prior antibiotic allergies
Antibiotic penetration - CNS infection, abscesses etc.
pH - aminoglycosides are much more effective in an alkaline medium
Potential side effects - linezolid – occurrence of pancytopenia after month of treatment Bactericidal (bc) vs. bacteriostatic agents - in life-threatening infections or in immunocompromised patients (bc) antibiotics are necessary
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7. General principles, Right X 3
All appropriate microbiological specimens, including blood cultures, should be obtained before commencing antibiotic therapy. An immediate Gram-stained report may indicate the appropriate antibiotic to use;
Blood cultures should be taken from a venepuncture site, after adequate skin antisepsis, and not from an intravenous or arterial catheter.
Antibiotics should be administered without delay.
The decision for empiric therapy, i.e. cover for the most ‘likely’ organisms causing any specific infection, must include various factors such as the site of the infecting organism (respiratory tract pathogens differ from those of abdominal infections), community versus hospital-associated infection; recent previous antibiotic prescription; ward versus ICU-acquired infection and knowledge of the organisms commonly grown in patients in any specific area.
Use a narrow-spectrum antibiotic whenever possible,
appropriate empirical choice for nosocomial sepsis, requires initial broad-spectrum antibiotics, even a combination, until culture and AST results are back and de-escalation should be implemented. Inappropriate and/or delayed appropriate antibiotic use in the ICU has been shown to have an impact on morbidity and mortality.
Evaluate the clinical response to treatment.
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8. Classification of antibiotics
Antibiotic activity
Bactericidal (the agent kills the bacteria) vs. bacteriostatic (the agent inhibits growth of the organism)
Chemical structure
Natural are metabolic by-products of soil microorganisms including fungi.
Semi-synthetic
Synthetic
Mechanisms of action.
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9. Antibiotics mechanisms of action
Effects on cell wall integrity
Inhibition of protein synthesis
Interference with nucleic acid metabolism
Inhibition of enzymes that synthesize folic acid, which automatically decreased synthesis of nucleotides and eventually inhibition of bacterial growth.
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10. Inhibition of cell wall synthesis
ß-lactams and glycopeptides
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11. The structure of cell wall
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12. Mechanism of action of ß-lactams
Penicillin and other ß-lactam antibiotics inactivate a set of transpeptidases (PBPs) that catalyze the final cross-linking reactions of peptidoglycan synthesis.
Penicillin inhibits these enzymes by inactivating them, forming an penicilloyl-enzyme complex.
PBPs are responsible for the assembly, maintenance, and regulation of the peptidoglycan structures
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13. Classification of penicillins and cephalosporins
First generation
Cefazolin
Second generation
Cefuroxim
Cefoxitin
Third generation
Cefotaxime
Ceftriaxone
Ceftazidime
Fourth generation
Cefepime
cefpirome
Natural penicillins
Penicillin G potassium
Penicillin V phenoxymethyl
Semisynthetic Penicillins
Penicillinase-resistant penicillins
Cloxacillin
Methicillin
Aminopenicillins
Ampicillin
Amoxicillin
Carboxypenicillins
Carbenicillin and ticarcillin
Ureidopenicillins
Piperacillin
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14. Other ß-lactam antibiotics
Carbapenems
Ertapenem
Imipenem-high affinity to high-molecular-weight PBPs.
Meropenem
Doripenem
Monobactams
Aztreonam
ß-lacatmase inhibitors protects from the hydrolytic activity of ß-lactamases by “suicide” inactivation (inhibitor is hydrolyzed):
Amoxicillin-clavulanate
Piperacillin-tazobactam
Ampicillin/sulbactam
Ceftolozane-tazobactam
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15. Glycopeptides Mechanism of action
Inhibit second stage of cell wall peptidoglycan synthesis by binding to the (D-alanyl-D-alanine precursor) peptide side chain, which fits into a “pocket” in the vancomycin molecule and that prevents assemble of the murein monomer into peptidoglycan.
These are representative antibiotics:
Vancomycin
Teicoplanin
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16. Inhibition of transpeptidation
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17. Macrolides, Lincosamide and Streptogramins-MLS (chemically unrelated but similar biologic properties) inhibit protein synthesis at 50s ribosomal subunit
Macrolides
Lincosamide
Streptogramins
erythromycin
clindamycin
Streptogramins: quinupristin and dalfopristin for treatment of GRE and GISA
azithromycin
clarithromycin
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18. Inhibition of protein synthesis
By interfering with protein synthesis at the ribosomal level.
By binding of the agent to either the 50s or 30s ribosomal subunit.
The final outcome which result in inhibition or killing of the organism depends on whether this binding is reversible or irreversible.
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19. Macrolides Mechanisms of action
A single molecule of the antibiotic reversibly binds to the 50S ribosomal subunit, and lead to inhibition of protein synthesis.
Other activities
Anti-inflammatory activities
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20. Macrolide members Macrolides are divided into 14, 15, and 16 members:
14-members are erythromycin, clarithromycin.
Ketolides are semisynthetic 14-member-ring macrolides with a 3-keto instead of a 3-OH, and possess:
Strong acid stability
Higher in vitro activity against gram positive cocci
Represented with telithromycin
15-member is azithromycin
16-members are carbomycin, josamycin and rokitomycin.
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21. Lincosamide - clindamycin
Clindamycin binds to 50S ribosomal binding site as other macrolides.
At low concentrations, clindamycin inhibits production of toxic-shock and other toxins by GAS and S. aureus.
Clindamycin is a bacteriostatic agent, but has a concentration-dependent bactericidal activity against staphylococci, streptococci, anaerobes, and H. pylori.
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22. Aminoglycosides Natural Natural-Micromonospora Semisynthetic
streptomycin
gentamicin
amikacin
neomycin
sisomicin
netilmicin
kanamycin
paramomycin
tobramycin
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23. Mechanism of action of aminoglycosides
Inhibition of protein synthesis by irreversible binding to the 30 S bacterial ribosomal subunit.
By displacing the cations (Ca and Mg), which makes outer membrane permeable and providing entry of the antibiotic.
Aminoglycosides interfere with the proofreading process that helps assure the accuracy of translation.
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24. Tetracyclines Mechanism of action
They penetrate by a pH-dependent process (passive diffusion) trough hydrophilic pores.
And trough cytoplasmic membrane by an energy dependent active transport system
Once inside the cell they binds reversibly to the 30S ribosomal subunit.
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25. Antibiotics inhibition of protein synthesis
Fusidic acid
Chloramphenicol
The exact mechanisms by which fusidic acid inhibit protein synthesis have not been fully explained.
Fusidic acid blocks elongation of polypeptide chain, by inhibiting ribosome-elongation factor.
Introduced in 1949, is one of many antibiotics derived from soil organisms of the genus Streptomyces.
Mechanism of action
Interferes with protein synthesis by binding to the prokaryotic 50S ribosomal subunit.
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26. Linezolid- the first oxazolidinone
Linezolid acts as an inhibitor of bacterial protein synthesis by blocking the formation of the 70s ribosomal initiation complex.
Against most susceptible bacterial species, linezolid is bacteriostatic.
Linezolid is bactericidal against pneumococci, GAS and anaerobes.
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27. Linezolid mechanism of action
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28. Antibiotics that interfere with DNA synthesis
Quinolones
Metronidazole
Rifampicin
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29. Mechanism of action of fluoroquinolones
Quinolones acts on enzymes -topoisomerases II (DNA gyrase in gram-negative bacteria) and topoisomerase IV (in gram positive bacteria). DNA gyrase inserts negative supercoils into DNA.
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30. Classification of quinolones
Narrow spectrum
nalidixic acid
Broad spectrum
ciprofloxacin
ofloxacin
norfloxacin
Expanded spectrum
levofloxacin
moxifloxacin
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31. Metronidazole Mechanism of action Enters bacteria via cell diffusion
Activates via single reduction step by bacteria forms radicals reacts with nuclear acid cell death by decreased intracellular concentration of unchanged drug which generates intermediate products which are toxic to the cell. These toxic transitory products interact with DNA, causing standard breaks and unwinding, resulting in cell death.
Spectrum of activity:
Anaerobic bacteria, microaerophilic bacteria, protozoa
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32. Rifampicin In the 1960s derived from Streptomyces mediterranei.
First line treatment of Mycobacterium tuberculosis.
Bactericidal effect by inhibition of DNA synthesis.
Adverse effects
Hepatotoxicity
Early phase hyperglycemia
Immune dysfunction (decreased albumin and T cell counts)
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33. Antibiotics that inhibit folate synthesis
Sulfonamide is similar in structure to para-aminobenzoic acid (PABA), which is used for folic acid synthesis (necessary for synthesis of nucleotides in bacterial and mammalian cells).
Inhibition of bacterial growth by competitively incorporating of PABA into tetrahydropteroic acid.
Trimethoprim (TMP) is a structural analogue of dihydropteroic acid, the first step in the synthesis of dihydrofolic acid sequential inhibitor of folic acid as well.
The combination TMP-SMX is synergistic against a wide spectrum of bacterial species.
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34. Steps trough folate synthesis
Pathway for the synthesis of tetrahydrofolic Acid, a cofactor needed for the synthesis of DNA and RNA nucleotides
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35. Overview of antibiotics and their actions
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36. New Antibiotics Tigecyclines
Broad spectrum glycylcycline
Semi-synthetic derivative of Minocycline
No activity against Pseudomonas aeriginosa due to efflux by MexXY-OprM (Jian Li Lancet infect Dis 2006
Activity against gram negative, gram positive, atypical, anaerobic and resistant bacteria.
This includes activity against MRSA, VRE and penicillin resistant Streptococcus pneumoniae.
Unlike existing tetracyclines, tigecycline is only available as an intravenous preparation, is administered twice daily.
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37. Mechanism of action
Glycylcyclines overcome key mechanisms of resistance
Glycylcyclines bind to the ribosome with five times higher affinity than tetracycline
Binds to the 30S ribosomal and blocks the entry of amino-acyl tRNA to the acceptor site
Inhibit protein synthesis and bacterial growth
Tigecyclines binds to additional sites of the ribosome in a manner not seen before, interfering with the mechanism of ribosomal protection proteins
Tigecyclines is not interfered by macrolide or tetracycline efflux pumps.
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38. Daptomycin
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39. Ceftolozane and tazobactam
Ceftolozane exhibits greater affinity for all essential PBPs 
In clinical trials, some but not all isolates of E. coli and K. pneumoniae producing beta-lactamases were susceptible to ZERBAXA (MIC ≤2 mcg/mL)
ZERBAXA is not active against bacteria that produce serine carbapenemases (K. pneumoniae carbapenemase [KPC]) and metallo-beta-lactamases
As shown in separate, surveillance studies CTX-M is the most prevalent ESBL group
The 3 most prevalent P. aeruginosa mechanisms of resistance are chromosomal AmpC, loss of outer membrane porin, and upregulation of efflux pumps.
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40. Thank you for attention!