The document discusses antimicrobial chemotherapy and antibiotic sensitivity testing. It provides definitions of antibiotics and antimicrobial agents, and describes the discovery of penicillin by Alexander Fleming in 1928. It then summarizes various classes of antibiotics including beta-lactams like penicillins and cephalosporins, aminoglycosides, tetracyclines, chloramphenicol, and others. The document also discusses mechanisms of action, resistance, and methods for detecting antibiotic sensitivity and resistance including disk diffusion, dilution, and E-test gradient testing.

1. Antimicrobial Chemotherapy and Antibiotic Sensitivity TestingDr.T.V.Rao MD
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2. Uses of Antimicrobial Agents
•Antimicrobial agents are widely employed to cure bacterial diseases
•Definition of Antibiotic –Antibiotics are substances that are derived from a various species of microorganisms and are capable of inhibiting the growth of other microorganism even in small concentrations.
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3. Beginning of Antibiotics with Discovery of Pencillin
•The discovery of penicillinhas been attributed to Scottish scientist Alexander Flemingin 1928 and the development of penicillin for use as a medicine is attributed to the Australian Nobel Laureate Howard Walter Florey.
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4. Discovery of Pencillin
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5. Discovery of Pencillin Awarded Nobel Prize
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6. Chemotherapeutic Agents
•Antimicrobial agents –that are produced synthetically but have action similar to that of antibiotics and are defined as chemotherapeutic agents
•Eg Sulphonamides, Quinolones. 11/1/2014 Dr.T.V.Rao MD 6

7. Definition
•Bacteriostatic-Antimicrobial agents that reversibly inhibit growth of bacteria are called as bacteriostic ( Tetracyclnes, Chloramphenicol )
•Bactericical –Those with an irreversible lethal action on bacteria are known as bactericidal ( Pencillin, Isoniazid )
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8. How Drugs Act
•Drugs differ on their capabilities to act at different sites on bacteria.
•Some drugs have more than one site of action
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9. Major mechanisms of antimicrobial drugs
•1 Inhibition of cell wall synthesis
•2 Inhibition of cell membrane function
•3 Inhibition of protein synthesis ( inhibition of translation and transcription of genetic material)
•4 Inhibition of nucleic acid synthesis.
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10. Pencillin
•Pencillin and cephalosporins act inhibiting Trans peptidases, the enzyme catalyses the final linking step in synthesis of peptidoglycan.
•Due to this reason Pencillin in bactericidal for grwoing bacteria since new peptidoglycan is synthesized at that stage only.
•In nongrwoing cells pencillin is inactive
•An intact beta –lactum is essential for antibacterial activity of pencillins
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11. Classification of Pencillins
•Natural
Benzyl pencillin
Phenoxymethyl pencillin Pencillin v
Semi synthetic and pencillase resistant
1 Methicillin
2 Nafcillin
3 Cloxacillin
4 Oxacillin
5 Floxacillin
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12. Extended spectrum pencillins
Aminopencillins -Ampicillin, Amoxycillin
Carboxypencillins –Carbencillin, Ticarcillin
Ureidopencillin -Piperacillin
Resistance to pencillin is due to pencillinase commonly called as ßlactamase
The enzyme opens Betalactam ring hydrolytically and thus converts the antibiotic to inactive pencillonic acid.
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13. Inhibitors to Beta lactamase
•Clavulinic acid which is a product of Strept.clavuligerus
•Acts against the Staphylococcal beta ßlactamase.
•And plasmid mediated Betalactamase of Gram negative bacteria.
•Salbactum –this is a semisyntetic sulfone derivative with weak antibacterial activity
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14. •Tazobactam –A penicillonic acid sulfone derivative acts well when combined with piperacillin.
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15. Cephalosporins
•Like pencillin acts similar
•Products of the molds of genus Cephalosporium except cefoxilin
•Divided into 4 generation of cephalosporins depending on the spectrum of activity.
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16. Different Generations of Cephalosporins
•Cephalosporins are grouped into "generations" based on their spectrum of antimicrobial activity. The first cephalosporins were designated first generation while later, more extended spectrum cephalosporins were classified as second generation cephalosporins.
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17. Major generations of Cephalosporins
•Cephalosporins are divided into 3 generations:
•1st generation: Cephelexin, cefadroxil, cephradine
•2nd generation: Cefuroxime, cefaclor
•3rd generation: cefotaxime, Ceftazidime, cefixime -these give the best CNS penetration
•4thgeneration Cephalosporins are already available
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18. Basis of generations in Cephalosporins
•Cephalosporins are grouped into "generations" based on their spectrum of antimicrobial activity. The first cephalosporins were designated first generation while later, more extended spectrum cephalosporins were classified as second generation cephalosporins.
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19. Advantages with Newer generations
•Each newer generation of cephalosporins has significantly greater gram-negative antimicrobial properties than the preceding generation, in most cases with decreased activity against gram-positive organisms. Fourth generation cephalosporins, however, have true broad spectrum activity
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20. Other Beta-lactams include
•Other beta-lactams include:
•Aztreonam: a monocytic beta-lactam, with an antibacterial spectrum which is active only against Gram negative aerobes, including Pseudomonas aeruginosa, Neisseria meningitidisand N. gonorrhoea.
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21. Other drugs
•Imipenem: a carbapenem with a broader spectrum of activity against Gram positive and negative aerobes and anaerobes. Needs to be given with cilastatin to prevent inactivation by the kidney.
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22. Quinolones
•Quinolones are the first wholly synthetic antimicrobials. The commonly used Quinolones.
•Act on the DNA gyrase which prevents DNA polymerase from proceeding at the replication fork and consequently stopping synthesis.
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23. Aminoglycosides
•Aminoglycosides are group of antibiotics in which amino sugars liked by glycoside bonds
•Eg Streptomycin,
•Act at the level of Ribosome's and inhibits protein synthesis
•Other Aminoglycosides –
Gentamycin, neomycins,paromomycins,tobramycins Kanamycins and spectinomycins
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24. Tetracycline's
•Broad spectrum antibiotic produced by Streptomyces species
•1. Oxytetracycle, chlortetracycle and tetracycline
•Tetracyclnes are bacteriostatic drugs inhibits rapidly multiplying organisms
•Resistance develops slowly and attributed to alterations in cell membrane permeability to enzymatic inactivation of the drug
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25. Choramphenicol
•Choramphenicol is bacteriostatic drug
•Can produce bone marrow depression
•Chloramphenicol interferes with protein synthesis.
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26. Macrolides,Azalides,Ketolides
•Contain macro cyclic lactone ring Erythromycin. Is popularly used drug
•Other drugs Roxithromycin,Azithromycin
•Inhibits the protein synthesis.
•Used as alternative to pencillin allergy patients.
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27. Other Antimicrobial agents
•Lincomycins
Clindamycin resembles Macrolides in biting site and antimicrobial activity.
Streptogramins
Quinpristin / dalfopristin
useful in gram postive bacteria
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28. Antibiotics in Anaerobes
•Major anaerobes –Anaerobic cocci, clostridia and Bacteroides are susceptible to Benzyl pencillin
•Bact.fragilis as well as many other anaerobes are treatable with Erythromycin,Lincomycin, tetracycline and Chloramphenicol
•Clindamycin is effective against many strains of Bacteroides
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29. Metronidazole in Anaerobic Infections
•Since the discovery of Metronidazole in 1973 since then it was identified as leading agent anaerobes.
•But also useful in treating parasitic infections
Trichomonas, Amoebiasis and other protozoan infections.
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30. Antiviral drugs
•Acyclovir
•Ribavirin
•Azidothymidine
•Amantidine
•Idoxuridine
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31. Antifungal Agents
•Grisofulvin
•Imidazole
•Polyenes Nystatin, Amphotericin B
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32. Antibiotic resistance
•Antibiotic resistanceis the ability of a micro organism to withstand the effects of antibiotics. It is a specific type of drug resistance. Antibiotic resistance evolves naturally via natural selectionacting upon random mutation, but it can also be engineered by applying an evolutionary stress on a population. Once such a geneis generated, bacteria can then transfer the genetic information in a horizontal fashion (between individuals) by plasmidexchange.
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33. Detection of Antibiotic sensitivity and Resistance
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34. Routine Susceptibility Tests
•Disk diffusion (Kirby Bauer)
•Broth micro- dilution MIC
–NCCLS reference method
•Etest
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35. •Diffusion method
–Put a filter disc, or a porous cup/a bottomless cylinder containing measured quantity of drugs on the a solid medium that has been seeded with test bacteria
•Dilution method
–vary amount of antimicrobial substances incorporated into liquid or solidmedia
–followed by inoculation of test bacteria Dr.T.V.Rao MD 35
Antimicrobial Susceptibility Testing
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36. Susceptibility Testing MethodsInnoculateMH platePlace diskson agar plateIncubate plate18-24 hr, 35 CMeasure and record zone of inhibition around each disk 11/1/2014 Dr.T.V.Rao MD 36

37. Antimicrobial susceptibility tests
Minimum inhibitory concentration [MIC]
–The smallest concentration of antibiotic that inhibits the growth of organism
Liquid media (dilution) allows MIC estimation
Solid media (diffusion)
–Disk diffusion (Kirby-Bauer)
–E-tests
–Allows MIC estimation
Beta lactamase production: quick screening method 11/1/2014 Dr.T.V.Rao MD 37

38. Disk Diffusion Susceptibility Testing
Improper agar & disk placement
Mueller Hinton agar &
good disk placement
Use Mueller Hinton agar
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39. Antimicrobial susceptibilitytesting using micro-broth dilutions
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• 96 well microtiter plateug/ml64 32 16 8 4 2
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40. Dilution in liquid broth
•Tubes containing increasing antibiotic concentrations
•Incubation during 18 hr at 37°C
•Tedious
0 (Control) 0,25 0,50 1 2 4 8mg/l
MIC
Bacterial growth
Inhibition
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41. Kirby-Bauer disc testing
Antibiotic-impregnated discs placed on an agar plate at the
interface between test organism and susceptible control organism
Resulting zones of inhibition compared, use of controls
Susceptibility is inferred (standard tables)
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42. Antimicrobial Gradient TestingE-test® Read platesafter recommendedIncubationRead MICwhere elipseintersectsscale
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43. Dr.T.V.Rao MD 43
E test –MIC Reports are helpful in Critical management decisions
•Quantitative MIC data is a prerequisite for the management of critical infections, including sepsis, especially among critical care patients. Etestis
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44. E-test
Plastic strips with a predefined
gradient of
– One antibiotic
– One antifungal
Only one manufacturer
One strip per antibiotic
Wide range of antibiotics
Easy to use
Storage at -20°C
Short shelf life, expensive

45. Reading E-tests
Susceptible <1
Resistant >4 ug/ml
Ciprofloxacin for Yersinia pestis
Intermediate 1-4 ug/ml
Upper reading
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46. Are we overusing Antibiotics
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47. Choose the Appropriate Antibiotic
Think before prescribing Are we using Right drug for the Right bug ?
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48. •Program created by Dr.T.V.Rao MD for Medical and Paramedical Students in the Developing world
•Email.
•doctortvrao@gmail.com
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