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Microbial Growth
For microorganisms, growth is measured by increase in cell number, due to their limited increase in cell size.
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Bacteria are classified by:
• Temperature Range• pH Range• Osmotic Pressure• Need for Oxygen
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Other Classifications
• Facultative: Microorganisms that can grow in more than one environment
• Obligate: Microorganisms that have specific environments strictly needed for growth
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Temperature Range
• Psychrophile: 0-30 degrees C range, 15 C optimum growth temperature
• Mesophile: 25-40 degrees C range, 37 C optimum growth temperature. These have most pathogens, optimized for body temperature.
• Thermophile: 40-110 degrees C range, 55 C optimum growth temperature.
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pH Range
• Acidophiles: Grow in acidic environment, pH less than 6.5. Linked to stomach ulcers.
• Neutrophiles: Grow in neutral environment, pH 6.5-7.5. Most pathogens are neutrophiles, as your body is mostly within this pH range.
• Alkaliphiles: Grow in basic environments, pH greater than 7.5.
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pH
• PH a factor in food spoilage: Canned food high in botulism
• Acid rain effect the environment• Bacteria often produce acids that eventually
interfere w/ their own growth.
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Osmotic Pressure Range
• Low osmotic pressure kills many prokaryotes.• Halophiles: microbes that can survive in salty
environments.• Obligate Halophiles: microbes that need salty
environments to survive.
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Nutritional Requirements for Growth
• Carbon: All living things need a carbon source• Nitrogen: used in protein and nucleic acid
synthesis• Sulfur: used in protein synthesis• Phosphorus: Used in ATP and nucleic acids• Trace Elements: (Fe, Zn, Cu, etc.) Co-factors
and co-enzymes to activate enzymes.
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Nutritional Requirements Cont.
• Trace Elements: (Fe, Zn, Cu, etc.) Co-factors and co-enzymes to activate enzymes. Only in small amounts.
• Organic Growth Factors are organic compounds that are essential to the organism but the organism is unable to synthesize it itself (ex. Vitamins, amino acids, nucleotides).
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Classifications for Oxygen Need
• Obligate Aerobes: Must have free oxygen for aerobic respiraiton.
• Obligate Anaerobes: Killed by free oxygen. Growth only occurs where there is no oxygen.
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Oxygen Needs Cont.
• Facultative Anaerobes: Have both aerobic and anaerobic growth. Growth is greater in the presence of oxygen because full respiration occurs.
• Aerotolerant anaerobes: Only anaerobic growth, but can tolerate the presence of oxygen. Growth occurs evenly throughout media as oxygen has no effect.
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Oxygen Needs Cont.
• Microaerophiles: Only aerobic growth. Oxygen is required in low concentrations. Growth occurs only where a low concentration of oxygen has diffused into the medium.
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Bacteria classified according to their Oxygen needs
• Obligate aerobes– Must have free oxygen for
aerobic respiration– Grow only occurs on top of
media where there is high concentration of oxygen
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Bacteria classified according to their Oxygen needs
• Falcutative Anaerobes– Both aerobic and anaerobic
growth– Growth is greater in the
presence of oxygen .– Growth occurs throughout
media.
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Bacteria classified according to their Oxygen needs
• Obligate anaerobes– killed by free oxygen– Growth occurs only
where there is no oxygen
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Bacteria classified according to their Oxygen needs
• Aerotolerant Anaerobes– Only anaerobic growth; but
can tolerate the presence of oxygen
– Growth occurs evenly throughout media as oxygen has no effect
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Bacteria classified according to their Oxygen needs
• Microaerophiles– Only aerobic growth– oxygen is required in low
concentrations.– Growth occurs only
where a low concentration of oxygen has diffused into medium
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Culture, Colony and Culture Media
• Culture: The actual bacteria being grown.• Colony: A group of the same bacteria growing
together.• Culture Media: What the bacteria are growing
on or in.
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Culture Media
Two types of culture media• Broth: A liquid nutrient media without agar• Agar: a common solidifying agent for a culture
medium.
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Agar
• It is added to nutrient medium to solidify it in order to bacterial grow colonies.
• It is made form seaweed. It has long been used in various foods from jellies, soups, and ice cream.
• Few microbes can break down agar.• Different freezing/melting points. Solid to liquid
at 94 C, liquid to solid at 42 C. Labs keep it liquid at 50 C
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Culture Media Cont.
• Chemically Defined: Medium in which the exact chemical composition is known. Often used to grow fastidious organisms. Expensive to buy.
• Complex: Used to grow most of the common bacteria and fungi that would be used in an introductory lab. Made of nutrients such as extracts from yeast, meat and plants.
• Anaerobic Growth Media/Reducing Media: No free oxygen and used to grown obligate anaerobes.
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Culture Media Cont.
• Selective: Media that is designed to suppress the growth of unwanted bacteria and encourage the growth of wanted bacteria.
• Differential: Makes it easier to distinguish colonies of the desired organism from other colonies growing on the same plate.
• Enrichment: Used to encourage the growth of a particular organism in a mixed culture. Example soil, fecal samples etc...