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MICROBIAL GROWTH

MICROBIAL GROWTH. Requirements for microbial growth. Physical Chemical. Physical. Temperature pH Osmotic pressure. Temperature. -10 to 20 o C, Psychrophiles. Temperature. 0 to 30 o C, Psychrotrophs. Temperature. 10 to 50 o C, Mesophiles Most pathogens. Temperature.

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MICROBIAL GROWTH

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  1. MICROBIAL GROWTH

  2. Requirements for microbial growth • Physical • Chemical

  3. Physical • Temperature • pH • Osmotic pressure

  4. Temperature • -10 to 20o C, Psychrophiles

  5. Temperature • 0 to 30o C, • Psychrotrophs

  6. Temperature • 10 to 50o C, • Mesophiles • Most pathogens

  7. Temperature • 40 to 70o C, thermophiles • 65 to 110o C, Extreme thermophiles

  8. Extreme thermophiles Thermophiles Mesophiles Psychrotrophs Psychrophiles -10 0 10 20 30 40 50 60 70 80 90 100 110 DegreesCentigrade

  9. pH • Most bacteria grow at pH 6.5 to 7.5 • Acidophiles (pH 1.0 - 5.5) Lactobacillus acidophilus

  10. pH • Alkalophiles (pH 8.5 - 11.5) Bacillus alcalophilus

  11. Osmotic Pressure (OP) • Bacteria are better adapted to low OP (i.e. tap water) • Plasmolysis occurs at high OP

  12. Osmotic Pressure (OP) (cont.) • Solutes (i.e. sugar and salt) limit water availability

  13. Osmotolerant Organisms (halophiles) • Less tolerant • Most Gram-negatives • More tolerant • Staphylococcus aureus • Fungi

  14. 2. DEEP-SEA VENT heat-loving microbes (Thermophiles and Hyperthermophiles) Methanopyrus kandleri 3. SULFURIC SPRING acid-loving microbes (Acidophiles) Sulfolobus acidocaldarius 4. SALT LAKE salt-loving microbes (Halophiles) Haloferax volcanii 5. SODA LAKE alkali-loving microbes (Alkaliphiles) Natronobacterium gregoryi 1. SEA ICE cold-loving microbes (Psychrophiles) Polaromonas vacuolata

  15. Chemical Requirements • Carbon (all organic compounds) • Nitrogen (proteins)

  16. Chemical Requirements (cont.) • Sulfur (proteins and vitamins) • Phosphorous (DNA, RNA, ATP)

  17. Trace Elements • Needed in minute amounts -Iron -Copper -Molybdenum -Zinc

  18. Trace Elements (cont.) • Present in high enough amounts in nature • Enzymatic activity • Cofactors

  19. Organic growth factors • Essential for growing • Vitamins • amino acids • Purines and pyrimidines

  20. Oxygen (O2) • Electron acceptor during aerobic respiration • More efficient than other acceptors (NO3, SO4, and CO3)

  21. Oxygen (O2) • Highly reactive oxygen radicals • Singlet oxygen • Superoxide free radicals

  22. Neutralization of oxygen radicals • Superoxide Dismutase (SOD) • Catalase

  23. Culture Medium Forms an oxygen gradient More Oxygen on top O2

  24. O2 Obligate Aerobes • Aerobic only (O2) Mycobacterium tuberculosis

  25. Facultative Anaerobes • Primarily aerobic • Alternatively anaerobic O2 Escherichia coli

  26. Obligate Anaerobes Clostridium spp. • Killed by • oxygen O2

  27. O2 Aerotolerant Anaerobes • Growth not affected by Oxygen Enterococcus faecalis

  28. O2 Microaerophiles • Aerobic • Killed by high (20%) O2 concentration Campylobacterspp.

  29. The Requirements for Growth: Chemical Requirements • Oxygen (O2) Aerotolerant aerobe Facultative anaerobe Microaerophilic Obligate aerobe Obligate anaerobe

  30. Bacterial Growth

  31. Binary fission • Asexualreproduction in which a cell separates into two cells

  32. Resting cell

  33. Cell elongation and DNA replication

  34. Cell wall and cell membrane grow inward

  35. Cell wall and Cell membrane meet

  36. Individual cells are formed

  37. Generation or Doubling Time • Time required for a cell to double in number • Highly variable, 20 minutes to 24 hours

  38. Generation Time (cont.) • Escherichia coli • 20 minutes • Mycobacterium tuberculosis • 12 hours

  39. 32 Escherichia coli’s generation time 16 8 4 2 1 0 20 40 60 80 100 120 140 Minutes Logarithmic growth

  40. Bacterial Growth Curve Number of bacteria Lag phase Time

  41. Bacterial Growth Curve Log Phase Number of bacteria Time

  42. Bacterial Growth Curve Stationary Phase Number of bacteria Time

  43. Bacterial Growth Curve Death Phase Number of bacteria Time

  44. Measurement of Microbial Growth • Plate counts • Pour plates

  45. Direct Measurements of Microbial Growth • Plate Counts: Perform serial dilutions of a sample Figure 6.15, top portion

  46. Serial Dilutions • Transfer of part of a sample through a series of specific volumes of diluent

  47. Serial Dilutions (cont.) • Reduce high numbers of microorganisms gradually (i.e. form 100,000,000 to 10)

  48. Membrane filtration Sterile cup Membrane 0.45 mm Vacuum

  49. Membrane filtration Culture medium

  50. Direct Measurements of Microbial Growth • Filtration Figure 6.17a, b

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