Mbi121 13 f12ctrlgrthnotes

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Mbi121 13 f12ctrlgrthnotes

  1. 1. Controlling Microbial Growth Chapter 12
  2. 2. Most microbes good, but…• where they are growing critical• yogurt = good• bloodstream = BAD• Nosocomial infections• Hygiene Hypothesis
  3. 3. Binary fission in bacteriaTo control growth, we need to stop or slow down this process Fig. 5.8
  4. 4. Cidal vs. Static
  5. 5. Control Methods
  6. 6. Physical Control• Heat: incineration vs. steam• Filtration• Temperature• Radiation• Desiccation (oven)
  7. 7. Physical Control - Heat• Bacteria can’t tolerate extreme temp changes – Fever• Protein denaturation - high fever
  8. 8. Heat• Dry heat – incineration
  9. 9. Heat• Dry heat - incineration• Moist heat - boiling water/steam – Kills most in seconds – Pasteurization - temp & time – What about endospores?
  10. 10. How can you get temp above boiling water?Temperature and the Physical Control of Microbes
  11. 11. Operation of an Autoclave
  12. 12. What types of items go in?• Medical instruments – Surgical – Dental – Piercing• Microbial media• Anything metal, some types of plastic
  13. 13. Physical Control• Refrigeration/freezing - microbes still there – cold temp slows down – Microbes can freeze/thaw and still reproduce
  14. 14. Physical Control• Radiation – UV – Ionizing
  15. 15. The Ionizing and Electromagnetic Spectrum of Energies Fig. 5.7
  16. 16. Physical Control - radiation• Radiation damages DNA• UV radiation (ultraviolet light) – UV lamps for disinfection – Causes T-T dimers – Cell death – What happens in humans?
  17. 17. Mutations block DNA processes• TT dimer distorts DNA• No replication• No transcription• High dose = death
  18. 18. Physical Control - radiation• Ionizing radiation (solar rays, radioactive) – 10K times more energy than UV – ionization of water (OH- & H3O+ ) – DNA breaks apart – Sterilize plastics, food, destroy viruses (Ebola) – What happens to humans exposed to IR? • Acute exposure - • Chronic exposure - • How do we know this???
  19. 19. Physical Control - desiccation• All living things need water• Dry out grains, meat, fish to preserve
  20. 20. Disinfectants/Antiseptics• Ancient Egypt - chemicals for embalming• 1800’s - Iodine used in medicine• Joseph Lister - 1860’s – Read Pasteur – soaked instruments in phenol – Knighted in 1912
  21. 21. Halogens • Halogens - extremely reactive • Interacts with amino acids - destroys cell membrane • Iodine – w/detergent • Chlorine – disinfect H2O
  22. 22. Alcohols• Denature proteins• Dry cells out• Disrupt lipid bilayer• No effect on endospores& some viruses
  23. 23. Phenolic Compounds• highly reactive – acidic• denature proteins – destroys cell membrane• first used by Lister – Lysol – Trichlosan - milder • potential for resistance?
  24. 24. Heavy Metals• Used as disinfectants - poison• Specific enzymes inhibited
  25. 25. Heavy Metals• Silver – Silver nitrate - eye infections (gonorrhea)• Copper – Copper Sulfate - swimming pools; antifungal• Mercury – antiseptics, pesticides
  26. 26. Antimicrobial Chemotherapy• Antibiotic control
  27. 27. Pre-antibiotic era• Medicine was a gruesome business• Civil war - more than 2/3 of all deaths due to disease, not wounds• Paul Erlich - early 1900s – Arsenic compounds as syphilis treatment – Fell out of favor b/c toxic
  28. 28. Sulfanilamide - sulfa drugs• 1932 - “prontosil” developed by Gerhard Domagk• Effective in treating Gram-positive bacterial infections• Gave push to development of newer & better antibiotics Bacteria need This PABA to make looks like folic acid PABA
  29. 29. Development of penicillin• Alexander Fleming• 1929 - Penicillium mold prevented S. aureus growth• Extract killed Gram-positive bacteria• 1939 - Florey & Chain• Mass produced in USA
  30. 30. Penicillin & derivatives• One of the most widely used antibiotics• Best against Gram-pos; some Gram-neg (gonorrhea)• ~ 10% of population allergic• Works on rapidly dividing cells – No effect on endospores!
  31. 31. Penicillin Derivatives
  32. 32. Penicillin Resistance• Many bacterial species have developed resistance• MRSA - methicillin resistant Staph. aureus
  33. 33. Streptomyces - natural antibiotic R&DSoil bacterium - lots of genes for making antibiotic compounds• Aminoglycoside (streptomycin, gentamycin) – Good if allergic to penicillin – Inhibits protein synthesis – Erythromycin: Zithromax, Biaxin – Vancomycin - last resort for MDR Gram-pos
  34. 34. Broad Spectrum antibiotics• Selective Toxicity• Chloramphenicol first one isolated – Effective against Gram-pos &neg, chlamydiae, some fungi – Nasty side effects - hemolytic (last resort)• Tetracycline – Very few side effects (short term) - overprescribed – Yeast infections common – Discoloration of teeth/stunted bones in children
  35. 35. Antibiotic Resistance• Emerging danger• Natural selection of resistant strains thru overuse – Overprescibing meds – Used in livestock feed
  36. 36. • Take entire course of prescription• Do not take higher dose of samemed if no improvement• Do not take antibiotics for viralinfection
  37. 37. How bacteria become resistant:
  38. 38. Antifungal meds• Fungal infections big problem for immune suppressed individuals• Antifungals - not many choices – Nystatin, miconazole - interfere w/sterols (cell membrane) – Amphotericin B - used for serious internal organ infection – Griseofulvin - ringworm treatment
  39. 39. Antiviral meds - not antibiotics• Antivirals target different stages of viral replication – amantadine - prevents attachment – acyclovir - interferes w/viral DNA replication

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