Bacterial Growth Factors

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  • Bacterial Growth Factors

    1. 1. Factors affecting microbial growth
    2. 2. Factors affecting microbial growth <ul><li>pH </li></ul><ul><li>Moisture </li></ul><ul><li>Nutrient Content </li></ul><ul><li>Oxygen </li></ul><ul><li>Light </li></ul>
    3. 3. pH <ul><li>Most spoilage bacteria grow best near neutral pH </li></ul><ul><li>  Pathogenic bacteria even more narrow in tolerance range of near neutral </li></ul><ul><li>  Yeast and moulds have much greater tolerance to acidic (lower) pH </li></ul>
    4. 4. pH <ul><li>The optimum pH range is usually quite narrow so that small changes in the pH can have large effects on the growth rate of the organism </li></ul>
    5. 5. pH <ul><li>Effects of acids on organisms </li></ul><ul><li>energy required to maintain cell's internal pH </li></ul><ul><li>enzyme activity affected </li></ul><ul><li>proteins, DNA, other molecules denatured </li></ul><ul><li>longer lag, less rapid growth </li></ul>
    6. 6. Moisture <ul><li>Microbes must have a supply of of water available </li></ul><ul><li>Bacteria most restricted, then yeasts, then moulds </li></ul><ul><li>Organisms tolerant of low water levels: </li></ul><ul><ul><li>halophilic bacteria osmophilic yeasts </li></ul></ul><ul><ul><li>xerophilic molds </li></ul></ul>
    7. 7. Moisture <ul><li>Effects of low water levels </li></ul><ul><ul><li>longer lag, slower growth </li></ul></ul><ul><ul><li>impaired transport </li></ul></ul><ul><ul><li>loss of membrane fluidity </li></ul></ul>
    8. 8. Nutrient content <ul><li>Required by all organisms: water, carbon, nitrogen, minerals </li></ul><ul><li>Organic growth factors needed to varying degrees: </li></ul><ul><ul><li>Gram + > Gram - > yeasts > moulds </li></ul></ul>
    9. 9. Nutrient content <ul><li>How easily are energy sources metabolized? </li></ul><ul><ul><li>sugar > alcohol > amino acids > complex molecules </li></ul></ul><ul><li>How easily are nitrogen sources metabolized? </li></ul><ul><ul><li>amino acids > proteins </li></ul></ul><ul><ul><li>B vitamins required by many bacteria </li></ul></ul>
    10. 10. Oxygen <ul><li>Obligate aerobes, e.g. Mycobacterium , will grow only in presence of free oxygen </li></ul>
    11. 11. Oxygen <ul><li>Facultative anaerobes, e.g. Saccharomyces (yeast) will grow in the absence of oxygen, but more slowly than if oxygen were present. </li></ul>
    12. 12. Oxygen <ul><li>Obligate anaerobes, e.g. Clostridium will grow only in absence of oxygen which is toxic to them </li></ul>
    13. 13. Light <ul><li>Essential for photoautotrophs. </li></ul><ul><li>As well as its intensity its wavelength may be significant. </li></ul>

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