Chapter 6

Chapter 6 - Microbial Growth Chapter 6 Microbial Growth -...

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Microbial Growth Chapter 6
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Microbial Growth - refers to the # of cells, not the size of the cells Requirements for Growth Physical Chemical
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Physical Requirements Temperature psychrophiles (cold loving microbes ) range 0 C - 20 C mesophiles (moderate temp. loving microbes) range 20 C - 40 C thermophiles (heat loving microbes) range 40 C - 100 C
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pH Most bacteria grow between pH 6.5 - pH 7.5 Very few can grow at below pH 4.0 many foods, such as sauerkraut, pickles, and cheeses are preserved from spoilage by acids produced during fermentation
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Osmotic Pressure Microbes obtain almost all their nutrients in solution from surrounding water Tonicity isotonic hypertonic hypotonic
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Cells
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Chemical Requirements C HOPKINS CaFe Mg NaCl
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Oxygen Bacteria can be classified base on their oxygen requirements
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1. Obligate Aerobes
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2. Obligate Anaerobes
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3. Facultative Aerobes Facultative Anaerobes
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4. Microaerophilic
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Oxygen is lethal to some organisms All organisms produce superoxide ( O 2 -) Superoxide is toxic to cells (steals electrons) Superoxide must be neutralized
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Superoxide dismutase O 2 - + O 2 - + 2 H + -------> H 2 O 2 + O 2 Hydrogen peroxide is also toxic to cells and it must be neutralized
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Chapter 6 - Microbial Growth Chapter 6 Microbial Growth -...

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