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Mbi121 13 f12ctrlgrthnotes
This document discusses various methods for controlling microbial growth, including physical, chemical, and antibiotic-based approaches. Physical methods include heat, filtration, temperature control, radiation, and desiccation. Chemical disinfectants and antiseptics discussed are halogens, alcohols, phenolic compounds, heavy metals, and antimicrobial drugs like sulfanilamide and penicillin. The development of antibiotic resistance in bacteria is also covered.
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Mbi121 13 f12ctrlgrthnotes
- 1. Controlling Microbial Growth Chapter 12
- 2. Most microbes good,but… • where they are growing critical • yogurt = good • bloodstream = BAD • Nosocomial infections • Hygiene Hypothesis
- 3. Binary fission inbacteria To control growth, we need to stop or slow down this process Fig. 5.8
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- 6. Physical Control • Heat: incineration vs. steam • Filtration • Temperature • Radiation • Desiccation (oven)
- 7. Physical Control -Heat • Bacteria can’t tolerate extreme temp changes – Fever • Protein denaturation - high fever
- 8. Heat • Dry heat– incineration
- 9. Heat • Dry heat- incineration • Moist heat - boiling water/steam – Kills most in seconds – Pasteurization - temp & time – What about endospores?
- 10. How can youget temp above boiling water? Temperature and the Physical Control of Microbes
- 11. Operation of anAutoclave
- 12. What types ofitems go in? • Medical instruments – Surgical – Dental – Piercing • Microbial media • Anything metal, some types of plastic
- 13. Physical Control • Refrigeration/freezing- microbes still there – cold temp slows down – Microbes can freeze/thaw and still reproduce
- 14. Physical Control • Radiation – UV – Ionizing
- 15. The Ionizing andElectromagnetic Spectrum of Energies Fig. 5.7
- 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. Mutations block DNA processes • TT dimer distorts DNA • No replication • No transcription • High dose = death
- 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. Physical Control -desiccation • All living things need water • Dry out grains, meat, fish to preserve
- 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. Halogens • Halogens - extremely reactive • Interacts with amino acids - destroys cell membrane • Iodine – w/detergent • Chlorine – disinfect H2O
- 22. Alcohols • Denature proteins • Dry cells out • Disrupt lipid bilayer • No effect on endospores& some viruses
- 23. Phenolic Compounds • highlyreactive – acidic • denature proteins – destroys cell membrane • first used by Lister – Lysol – Trichlosan - milder • potential for resistance?
- 24. Heavy Metals • Usedas disinfectants - poison • Specific enzymes inhibited
- 25. Heavy Metals • Silver – Silver nitrate - eye infections (gonorrhea) • Copper – Copper Sulfate - swimming pools; antifungal • Mercury – antiseptics, pesticides
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- 27. Pre-antibiotic era • Medicinewas 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
- 30. Sulfanilamide - sulfadrugs • 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
- 31. Development of penicillin •Alexander Fleming • 1929 - Penicillium mold prevented S. aureus growth • Extract killed Gram-positive bacteria • 1939 - Florey & Chain • Mass produced in USA
- 32. 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!
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- 34. Penicillin Resistance • Manybacterial species have developed resistance • MRSA - methicillin resistant Staph. aureus
- 35. Streptomyces - naturalantibiotic R&D Soil 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
- 36. 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
- 37. Antibiotic Resistance • Emergingdanger • Natural selection of resistant strains thru overuse – Overprescibing meds – Used in livestock feed
- 38. • Take entirecourse of prescription • Do not take higher dose of same med if no improvement • Do not take antibiotics for viral infection
- 40. How bacteria becomeresistant:
- 41. Antifungal meds • Fungalinfections 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
- 42. Antiviral meds -not antibiotics • Antivirals target different stages of viral replication – amantadine - prevents attachment – acyclovir - interferes w/viral DNA replication