antimicrobial chemotherapy


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This is a series of lectures on microbiology useful for undergraduate medical and paramedical students

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antimicrobial chemotherapy

  1. 1. ANTI MICROBIAL CHEMOTHERAPY Dr. Ashish Jawarkar M.D. Consultant Pathologist Parul Sevashram Hospital
  2. 2. Modern era in Antibiotics begins with Fleming.
  3. 3. Definition - Antibiotic      Anti – against Bio – life Originally extracted from compounds produced by living organisms – aminoglycosides Semi synthetic – cephalosporins, carbapenems Synthetic – sulphonamides, quinolones, oxazolidinediones
  4. 4. History of Antibiotic Discovery
  5. 5. Mechanisms of antibacterial action
  6. 6.  1. Inhibition of cell wall synthesis   2. Inhibition of protein synthesis   Aminoglycosides, tetracyclines, chloramphenicol, macrolides 3. Alteration of cell membranes   Penicillin, vancomycin, bacitracin Polymyxin B, Bacitracin 4. Inhibition of nucleic acid synthesis DNA – quinolones, Metronidazole  RNA – Rifampicin, Bacitracin   5. Antimetabolite activity  Sulfonamides
  7. 7. Antimicrobial Resistance    How bacteria survive doses of antibiotics that would otherwise have been lethal Problem – treated with a higher dose, or newer antibiotic Side effects, Newer may not be available
  8. 8. Types of resistance  Intrinsic   Bacteria may not make the protein that antibiotic targets Extrinsic  Due to acquired mutation in DNA or RNA
  9. 9. Causes of Resistance   Overuse/misuse of antibiotics Example is sore throat – Viral , still antibiotics are prescribed Failure to take entire course  Failure to take at correct intervals – two times a day instead of three times 
  10. 10. Antibiotic Susceptibility Testing   Pathogenic bacteria show large variations in susceptibility to antibiotics Particularly marked in case of Staphylococcus and gram negative bacteria
  11. 11. Types   Diffusion tests Dilution tests
  12. 12. Uses of Antibiotic Sensitivity Testing    Antibiotic sensitivity test: A laboratory test which determines how effective antibiotic therapy is against a bacterial infections. Antibiotic sensitivity testing will control the use of Antibiotics in clinical practice Testing will assist the clinicians in the choice of drugs for the treatment of infections.
  13. 13. Components of Antibiotic Sensitivity Testing   1.The identification of relevant pathogens in exudates and body fluids collected from patients 2. Sensitivity tests done to determine the degree of sensitivity or resistance of pathogens isolated from patient to an appropriate range of antimicrobial drugs
  14. 14. Antibiotic Sensitivity Testing Is Essential of selection of Antibiotics
  15. 15. Isolation and Identification of Bacteria precedes the selection of Antibiotic Testing Methods
  16. 16. Uses of Antibiotic Sensitivity Testing    Helps to guide the Physician in choosing Antibiotics The accumulated results on different pathogens their sensitivity will guide the physician in choosing empirical treatment in serious patients before the individual’s laboratory results are analyzed in the Microbiology laboratory. Reveals the changing trends in the local isolates.
  17. 17. Why Need continues for testing for Antibiotic Sensitivity  Bacteria have the ability to develop resistance following repeated or subclinical (insufficient) doses, so more advanced antibiotics and synthetic antimicrobials are continually required to overcome them.
  18. 18. Testing for Antibiotic sensitivity    The method includes several steps including obtaining a bacterial sample; identifying the type of bacteria in the bacterial sample; selecting a set of antibiotics based on the identity of the bacteria in the bacterial sample; obtaining a control sample from the bacterial sample;
  19. 19. What is Resistance in Antibiotic Sensitivity Testing  Resistance implies that the infection is not treatable with the tested Antibiotic because its MIC exceeds achievable safe tissue or urine levels.
  20. 20. Kirby-Bauer methods A commonly used method in basic laboratories  Kirby-Bauer antibiotic testing (KB testing or disk diffusion antibiotic sensitivity testing) is a test which uses antibiotic-impregnated wafers to test whether particular bacteria are susceptible to specific antibiotics
  21. 21. How to perform Kirby- Bauer testing  The basics are easy: The bacterium is swabbed on the agar and the antibiotic discs are placed on top. The antibiotic diffuses from the disc into the agar in decreasing amounts the further it is away from the disc. If the organism is killed or inhibited by the concentration of the antibiotic, there will be NO growth in the immediate area around the disc: This is called the zone of inhibition .
  22. 22. Steps in Antibiotic sensitivity testing
  23. 23. Bacteria are inoculated as lawn culture  Method of inoculationGood results are obtained by placing a standard loopful of inoculum suspension on the plate and then spreading it with a dry sterile swab.
  24. 24. The area of Inhibition is measured with a Scale  Record the results for everyone on your table in the table below.
  25. 25. The disk diffusion methods are commonly used for routine testing
  26. 26. Read the plates in transmitted light
  27. 27. The zone of inhibition guides the right choice of Antibiotic
  28. 28. The strips with multiple Antibiotics can be tested in one go
  29. 29. Other methods of Antibiotic susceptibility testing  Other methods to test antimicrobial susceptibility include the Stokes method, E-test (also based on antibiotic diffusion). Agar and Broth dilution methods for Minimum Inhibitory Concentration determination.
  30. 30. Testing Minimum Inhibitory Concentration  In alternative measure of susceptibility is to determine the Minimum Inhibitory Concentration (MIC) and the Minimum Bactericidal Concentration (MBC) of a drug. A series of broths are mixed with serially diluted antibiotic solutions and a standard inoculum is applied. After incubation, the MIC is the first broth in which growth of the organism has been
  31. 31. What is Minimum Inhibitory concentration  Minimum inhibitory concentration (MIC), in microbiology, is the lowest concentration of an antimicrobial that will inhibit the visible growth of a micro organism after overnight incubation. Minimum inhibitory concentrations are important in diagnostic laboratories to confirm resistance of micro organisms to an antimicrobial agent and also to monitor the activity of new antimicrobial agents.[
  32. 32. The Antibiotics are diluted to various dilution to test the minimum inhibitory concentration
  33. 33. What is E Test  Etest is an antimicrobial gradient technique in which 15 reference MIC dilutions of an antibiotic have been repackaged with innovative dry chemistry technology onto a plastic strip. The predefined gradient provides precise and accurate assessment of antimicrobial activity against both fastidious and non-fastidious microorganisms.  Dr.T.V.Rao MD
  34. 34. The s t ri ps are im pregnat ed w t h vari ous i c onc ent rat i on of Ant i bi ot i c s
  35. 35. E = testing on various isolates
  36. 36. Limitation of Disk Diffusion Methods   Disk diffusion methods are not suitable for slow growing bacterial pathogens The great limitation being for testing on Mycobacterium tuberculosis which needs varied, technically demanding methods
  37. 37. Antibiotic Sensitivity testing can be done with automation
  38. 38. There is a growing need for Automation in Antibiotic sensitivity testing
  39. 39. Limitation of Antibiotic Sensitivity usage Both Microbiologists and Clinician should however bear in mind that the response therapy in vivo may not always reflect the results of testing the sensitivity of patient's pathogen in vitro.
  40. 40. Thank You