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Questions and Answers
What is generation time in bacterial growth?
During which phase of the bacterial growth curve do disease symptoms typically develop?
Which method is used to isolate pure bacterial colonies?
What does it mean for an organism to be in a VBNC state?
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Which of the following classifications of bacteria can utilize aerobic respiration?
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What is the purpose of the Gaspak system in microbial cultivation?
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What does a positive catalase test indicate about an organism?
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What pH classification do organisms that grow best in acidic conditions fall under?
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Which group of bacteria is known to grow best at temperatures exceeding 80 degrees Celsius?
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Psycrotrophs are distinct from psychrophiles in which way?
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What characterizes psychrotrophs compared to psychrophiles?
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Which type of bacteria is most likely to thrive in human body temperature?
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How does Helicobacter pylori survive the acidic environment of the stomach?
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What defines a barophile?
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Which statement accurately describes halophiles?
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What is a key difference between complex and synthetic media?
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Which type of media is designed to inhibit the growth of some organisms while promoting others?
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What is the main purpose of differential media?
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How is enriched media different from selective media?
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Which bacteria is classified as a neutrophile yet survives in acidic conditions?
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Study Notes
Generation Time
- Time required for a bacterial cell to divide and double in number via binary fission.
Bacterial Growth Curve
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Lag Phase: No increase in living bacterial cells, cells are preparing for growth.
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Log (Exponential) Phase: Large increase in living bacterial cells, cells are actively dividing and growing.
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Stationary Phase: Plateau in the number of living bacterial cells, cell division and death are equal.
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Death Phase: Large decrease in living bacterial cells, cells are dying at a faster rate than they are dividing.
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Disease symptoms often develop during the Log Phase.
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Antibiotics are most effective during the Log Phase as cells are actively multiplying.
Counting Bacteria
- Direct Microscope Count: Counts all cells, including living and dead, with a microscope.
- Fluorescence Microscopy: Uses fluorescent dyes to differentiate between live and dead cells.
- Coulter Counter: Counts cells by passing them through a small opening, disruption of electrical field registers cell passage.
- Standard Plate Count: Counts viable cells capable of forming colonies on an agar plate.
- Optical Density: Measures turbidity (cloudiness) of a culture, indirectly proportional to cell concentration.
Streak Plate Method
- Aims to isolate pure bacterial colonies by diluting cells on an agar plate, facilitating the growth of single cells that form individual colonies.
Viable But Non-Culturable (VBNC)
- A living organism that cannot be cultured in standard laboratory conditions.
Oxygen Requirements
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Obligate Aerobes: Require oxygen for respiration.
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Facultative Anaerobes: Can grow with or without oxygen, but prefer oxygen for respiration.
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Obligate Anaerobes: Cannot tolerate oxygen, can only grow in the absence of oxygen.
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Microaerophiles: Require low oxygen concentrations to grow.
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Aerotolerant Anaerobes: Tolerate oxygen but do not use it for respiration.
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Obligate aerobes, Facultative Anaerobes, and Microaerophiles can undergo aerobic respiration.
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Facultative Anaerobes, Aerotolerant Anaerobes, and Obligate Anaerobes can undergo fermentation.
Gaspak System
- Creates an anaerobic environment for cultivating microorganisms sensitive to oxygen, by consuming oxygen and replacing it with nitrogen.
Capnophile
- A microorganism that thrives in high carbon dioxide concentrations.
Catalase Test
- Detects the presence of catalase enzymes, which are present in organisms that can detoxify hydrogen peroxide, a byproduct of aerobic respiration. A positive test indicates the ability to undergo aerobic respiration.
Optimal pH
- Acidophiles: Grow best in acidic conditions (pH below 5.5).
- Neutrophiles: Grow best in neutral pH conditions (pH between 5.5 and 8.5).
- Alkalophiles: Grow best in basic conditions (pH above 8.5).
Optimal Temperature
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Psychrophiles: Grow best at temperatures between 0 and 15°C.
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Mesophiles: Grow best at temperatures between 20 and 45°C.
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Thermophiles: Grow best at temperatures between 45 and 80°C.
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Hyperthermophiles: Grow best at temperatures above 80°C.
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Psychrophiles are restricted to colder temperatures, while Psychrotrophs can grow at lower temperatures but have a wider temperature range.
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Most pathogenic bacteria are Mesophiles, thriving at human body temperature.
Helicobacter Pylori
- Can survive in the highly acidic environment of the stomach, despite being a neutrophile, by producing urease. Urease converts urea into ammonia, neutralizing stomach acid and creating a more favorable pH.
Barophile
- An organism that thrives at high-pressure environments, often found in deep-sea habitats.
Halophile
- An organism that thrives in high salt environments, allowing them to survive in environments like salt lakes or salty foods.
Media Types
- Complex Media: Contains a variety of nutrients of unknown chemical composition.
- Synthetic Media: Contains known chemical compositions of nutrients.
Media Classifications
- Selective Media: Supports the growth of specific microorganisms while inhibiting the growth of others.
- Differential Media: Distinguishes between different microorganisms based on their growth characteristics.
- Enriched Media: Contains extra nutrients to support the growth of fastidious organisms requiring specific or extra nutrients.
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Description
Explore the various phases of bacterial growth, including the lag, log, stationary, and death phases. Understand the significance of these phases in relation to disease symptoms and antibiotic effectiveness. Additionally, learn about different methods for counting bacteria, such as direct microscope count and fluorescence microscopy.
