ANTIMICROBIAL%20AGENTS - PowerPoint PPT Presentation

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ANTIMICROBIAL%20AGENTS

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Title: ANTIMICROBIAL%20AGENTS


1
ANTIMICROBIAL AGENTS
2
  • ANTIBIOTICS
  • ANTIMICROBIAL AGENTS
  • CHEMOTHERAPEUTIC AGENTS

3
ANTIBIOTICS
  • Natural substances produced by various species of
    microorganisms
  • bacteria
  • fungi
  • actinomycetes
  • suppress growth / kill other microorganisms

4
ANTIMICROBIAL AGENTS
  • Synthetic analogues
  • ANTIMICROBIAL AGENTS
  • includes synthetic as well as naturally obtained
    drugs that attenuate microorganisms

5
CHEMOTHERAPEUTIC AGENTS
  • Drugs in this class differ from all others in
    that they are
  • Designed to inhibit/kill the infecting organism
    and have no/minimal effect on the recipient.

6
  • Classification
  • Of AMAs

7
  • Microorganisms of medical impotance fall into
    four categories
  • Bacteria
  • Viruses
  • Fungi
  • Parasites

8
  • Anti-bacterial
  • Anti-viral
  • Anti-fungal
  • Anti-parasitic agents

9
Mechanism of Action
  • Agents that inhibit synthesis of bacterial cell
    walls
  • Penicillins cephalosporins
  • Cycloserine,
  • Vancomycin
  • Bacitracin
  • Azole antifungal agents (clotrimazole,
    fluconazole, itraconazole)

10
  • Agents that act directly on the cell membranes of
    the microorganisms
  • Polymixin
  • Polyene antifungal agents
  • (Nystatin, Amphotericin B)
  • Alter cell memb. Permeability,
  • leakage of intracellular comp.

11
  • Agents that affect the function of 30S or 50S
    ribosomal subunits to cause a reversible
    inhibition of protein synthesis
  • Bacteriostatic drugs
  • Chloramphenicol, Tetracyclines,
    Erythromycin, Clindamycin, Pristinamycins

12
  • Agents that bind to 30S ribosomal subunit
    alter protein synthesis, which eventually leads
    to cell death
  • Aminoglycosides

13
  • Agents that affect bacterial nucleic acid
    metabolism.
  • Rifamycins which inhibit RNA polymerase
  • Quinolones which inhibit topoisomerases

14
  • Anti-metabolites
  • including trimethoprim sulphonamides
  • Antiviral agents
  • Nucleic acid analogues,
  • Non-nucleoside reverse transcriptase
    inhibitors,
  • Inhibitors of viral enzymes

15
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16
TYPE OF ACTION
  • Bacteriostatic Agents
  • Bactericidal Agents

17
  • Bacteriostatic Agents
  • Sulphonamides
  • Tetracyclines
  • Chloramphenicol
  • Erythromycin
  • Ethambutol

18
  • Bactericidal Agents
  • Penicillins/Cephalosporins/Carbapenems
  • Aminoglycosides
  • Rifampin
  • Isoniazid
  • Pyrazinamide

19
  • Cephalosporins
  • Vancomycin
  • Nalidixic acid
  • Ciprofloxacin
  • Metronidazole
  • Cotrimoxazole

20
  • Some primarily static drugs may become cidal at
    higher concentrations (as attained in the urinary
    tract) vice-versa.

21
SPECTRUM Of ACTIVITY
  • Narrow spectrum
  • Broad spectrum

22
SPECTRUM Of ACTIVITY
  • Narrow spectrum Penicillin G Streptomycin
  • Broad spectrum
  • Tetracyclines
  • Chloramphenicol

23
Successful Antimicrobial Therapy
  • Concentration site of infection
  • Concentration should inhibit microorganisms
  • simultaneously it should be below the level
    toxic to human beings.
  • Host Defences
  • Immunity intact - Bacteriostatic Agents
  • Impaired immunity - Bactericidal Agents

24
Source of antibiotics
  • Fungi
  • Bacteria
  • Actinomycetes.

25
Source of antibiotics
  • Fungi
  • Penicillin, Griseofulvin, Cephalosporin
  • Bacteria
  • Polymyxin B, Colistin, Bacitracin, Aztreonam.
  • Actinomycetes.
  • Aminoglycosides, Macrolides, Tetracyclines,
    Polyenes, Chloramphenicol

26
  • Resistance

27
Bacterial resistance to ANTIMICROBIAL AGENTS
  • 3 general categories
  • Drug does not reach its target
  • Drug is not active
  • Target is altered

28
Drug does not reach its target
  • Porins
  • Absence/mutation
  • Reduce drug entry
  • Reduced effective drug concentration at the
    target site.
  • Efflux pumps
  • Transport drugs out of the cell
  • Resistance to tetracyclines ß-lactam antib

29
Inactivation of Drug
  • Second general mechanism of drug resistance
  • ß-lactam antibiotics - ß-lactamase
  • Aminoglycosides - Aminoglycoside modifying
    enzymes
  • Variant failure of bacterial cell to convert an
    inactive drug to its active metabolite.
    Resistance to INH in mycobacterium TB

30
Alteration of the Target
  • Mutation of natural target
  • Target modification
  • The new target does not bind the drug for native
    target
  • Resulting in resistance to antibiotic.

31
  • Components mediating resistance to ß lactam
    antibiotics in psuedomonas aeruginosa

32
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33
  • ß lactam antibiotics hydrophilic
  • Must cross outer membrane barrier of the cell via
    outer membrane protein (Omp) channel or porins
  • Mutation/missing/deleted
  • Drug entry slow or prevented.

34
  • ß - lactamase concentrated between the inner
    outer membrane in the periplasmic space
  • constitutes an enzymatic barrier
  • Drug destroyed
  • Effective concentration not achieved

35
  • Target PBP penicillin binding protein
  • Low affinity for drug
  • Altered

36
  • Efflux transporter
  • Mex A, Mex B Opr F
  • Pumps the antibiotic across the outer membrane
  • Reduced intracellular concentration of active
    drug
  • RESISTANCE

37
Mutations
  • May occur in
  • Target protein
  • Drug transport protein
  • Protein important for drug activation
  • Random events
  • Survival advantage upon re-exposure to the drug

38
  • Resistance is acquired by horizontal transfer of
    resistance determinants from a donor cell, often
    of another bacterial species by
  • Transduction
  • Transformation
  • Conjugation

39
  • Insatiable need for new antibiotics

40
  • Emergence of antibiotic resistance in bacterial
    pathogens both nosocomially in the community
    setting is a very serious development that
    threatens the end of antibiotic era.

41
  • Responsible approach to the use of antibiotics
  • That are now available new agents that might be
    developed in future
  • Is essential
  • If the end of antibiotic era is to be averted.

42
  • CROSS RESISTANCE

43
CROSS RESISTANCE
  • Acquisition of resistance to one AMA conferring
    resistance to another antimicrobial agent to
    which the organism has not been exposed,is called
    cross resistance
  • Seen b/w chemically or mechanistically related
    drugs.

44
  • Resistance to one sulphonamide means resistance
    to all others
  • Resistance to one tetracyclines means
    insenstivity to all others
  • Complete cross resistance

45
  • Resistance to one aminoglycoside may not extend
    to others, Gentamycin resistant strains may
    respond to amikacin.
  • partial cross resistance

46
  • Sometimes unrelated drugs show partial cross
    resistance,
  • e.g. Tetracyclines
  • Chloramphenicol

47
  • Prevention DRUG RESISTANCE

48
Prevention DRUG RESISTANCE
  • Use of AMAs should not be
  • indiscriminate
  • inadequate
  • unduly prolonged
  • Use rapidly acting narrow spectrum (Selective)
    AMA whenever possible.

49
Prevention DRUG RESISTANCE
  • Combination AMA
  • whenever prolonged therapy is undertaken.
    Tuberculosis, SABE
  • Infection by organism notorious for developing
    resistance Staph, E. Coli, M. Tuberculosis must
    be treated intensively.
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