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Microbe Control

This overview explores the various environmental factors influencing microbial growth and control methods. Key aspects include temperature, radiation, pressure, pH, and moisture levels, which significantly impact microorganisms like *Thermocrinis ruber* and *Deinococcus radiodurans*. It delves into sterilization and disinfection techniques, such as boiling, autoclaving, and irradiation, as well as the pH preferences of different microbes, especially bacteria and molds. Culturing techniques and tests like MacConkey agar are also discussed, highlighting their importance in identifying specific bacteria.

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Microbe Control

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  1. Microbe Control • Environmental Controls • Temperature • Radiation • Pressure • pH • Moisture • Control Methods

  2. Temperature • Growth Temperature • Maximum • Optimum • Minimum • Heat • Cold Thermocrinis ruber

  3. Radiation • Blue Light • UV • X-rays • Gamma Rays • Photoreactivation Deinococcus radiodurans

  4. Pressure • Piezophile • Barophile • Obligate barophiles • Pseudomonas bathecetes

  5. pH • Most • Marine • Molds vs. Bacteria • Molds like lower pH than bacteria • Acidophiles Acidic mud pot in Yellowstone Park – home to the acidophile Sulfolobus acidocaldarius. Credit: US National Park Service http://www.brooklyn.cuny.edu/bc/ahp/CellBio/Growth/MGpH.html

  6. Moisture • Bacteria vs Molds • Bacteria like more moisture than molds • Food Preparation • Dried Foods • Freeze-Dried Foods • “Cured” Foods

  7. Microbe Control Methods • TERMS: • Sterilize • Kill or remove all life present • Disinfect • Kill pathogens present • Germicide • Antiseptic • Sanitize • Make safe to use or eat from

  8. Ways to Sterilize & Disinfect STERILIZE • Burning • Boiling • Autoclave (pressure cook) • Filtration • Irradiation • Chemicals • Iodine • Chlorine DISINFECT • Detergents/Soaps • Acids & Bases • Alcohols • Mercury • Cresols • Hydrogen peroxide • Formalin • Antibiotics

  9. Pasteurization • Louis Pasteur • Internal temperature • Batch (Vat) • HTST • UP

  10. Growth (Culture) of Microbes • Natural media • Extracts • Infusions • Synthetic media • Nutrient broth • Nutrient agar

  11. Broth Solidifiers Which is useful for incubation at human body temperature? Gelatin Animal protein Melts @ 20°C Digested by microbes Agar Plant carbohydrate Melts @ ~100°C, solidifies @ ~42°C NOT digested by (terrestrial) microbes

  12. Culturing Techniques • Researchers use specific compounds and substrates in the culture medium and observe what grows! • MacConkey agar • Isolates enteric, Gram-negative, bacteria based on their ability to ferment lactose

  13. SIM Test • S = Sulfur reduction • I = Indole production • Kovac’s reagent • M = Motility

  14. Simmons Citrate Test • Tests the ability of certain organisms to utilize citrate as a carbon source. • pH indicator = Bromthymol blue • pH > 7.5 turns royal blue • Neutral pH green (just like uninoculated media)

  15. Christensen Urea Test • Some bacteria utilize urea, which results in the formation of ammonia. • Alkaline • Produces a red-pink/red-violet color • A negative reaction will have no color change and the agar medium will remain pale yellow.

  16. Identifying Specific Bacteria

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