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Questions and Answers
What defines essential growth factors for bacteria?
What defines essential growth factors for bacteria?
- They enhance growth without being necessary.
- They are indispensable for bacterial growth. (correct)
- They can be synthesized by the bacteria.
- They are required in minute quantities.
Which culture technique is primarily used to isolate a single colony of bacteria?
Which culture technique is primarily used to isolate a single colony of bacteria?
- Stroke culture
- Lawn culture
- Streak culture (correct)
- Pour plate
What is the main purpose of lawn culture?
What is the main purpose of lawn culture?
- To test antibiotic sensitivity. (correct)
- To isolate bacteria in streaks.
- To culture bacteria for sterility tests.
- To prepare bacterial antigens.
What does the stab culture technique involve?
What does the stab culture technique involve?
Which culture technique is suitable for maintaining a stock culture?
Which culture technique is suitable for maintaining a stock culture?
In which method does the inoculum get stretched out across the surface of the agar plate?
In which method does the inoculum get stretched out across the surface of the agar plate?
Which of the following statements about growth factors is false?
Which of the following statements about growth factors is false?
Which characteristic is unique to pour plate culture?
Which characteristic is unique to pour plate culture?
What is the primary process through which bacteria multiply?
What is the primary process through which bacteria multiply?
During which phase of the bacterial growth curve does the number of new cells produced equal the number of cells that die?
During which phase of the bacterial growth curve does the number of new cells produced equal the number of cells that die?
What is the generation time for Escherichia coli?
What is the generation time for Escherichia coli?
What type of cell count includes both living and dead cells?
What type of cell count includes both living and dead cells?
Which bacterial species has the longest generation time among the following?
Which bacterial species has the longest generation time among the following?
What characterizes the lag phase of the bacterial growth curve?
What characterizes the lag phase of the bacterial growth curve?
Which of the following conditions are bacteria most likely to face during the stationary phase?
Which of the following conditions are bacteria most likely to face during the stationary phase?
What is true about the log phase in bacterial growth?
What is true about the log phase in bacterial growth?
What characteristic defines mesophilic bacteria?
What characteristic defines mesophilic bacteria?
Which type of bacteria requires the presence of oxygen for growth?
Which type of bacteria requires the presence of oxygen for growth?
Which of the following statements about osmotic effects on bacteria is true?
Which of the following statements about osmotic effects on bacteria is true?
What effect does drying have on bacterial cells?
What effect does drying have on bacterial cells?
How are acidophiles classified concerning pH levels?
How are acidophiles classified concerning pH levels?
Which of the following is a requirement for bacteria to grow and multiply?
Which of the following is a requirement for bacteria to grow and multiply?
Which type of bacteria can utilize atmospheric CO2 and N2 for growth?
Which type of bacteria can utilize atmospheric CO2 and N2 for growth?
Which of the following types of radiation is lethal to bacteria?
Which of the following types of radiation is lethal to bacteria?
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Study Notes
Learning Objectives
- Classify bacteria based on growth requirements with examples.
- Describe the process and stages of bacterial growth.
- Discuss the essential requirements for bacterial growth.
Bacterial Growth
- Growth refers to an increase in cell components leading to population multiplication.
- Bacteria reproduce by binary fission, resulting in generation time.
- Example: E. coli (20 min), Mycobacterium tuberculosis (20 hours), Mycobacterium leprae (20 days).
Bacterial Counts
- Bacterial growth can be assessed by:
- Total cell count: includes living and dead cells.
- Viable cell count: only living cells.
- Counting methods: direct counting using microscopy techniques.
Bacterial Growth Curve
- Involves tracking bacterial numbers over time in a nutrient medium.
- Phases of the growth curve:
- Lag Phase: Adaptation period, no cell division, metabolic activity present.
- Log Phase: Rapid cell division, antibiotics most effective during this stage.
- Stationary Phase: Balance of new cells produced and dying cells due to nutrient depletion.
- Death Phase: Decline in viable bacteria numbers.
Factors Affecting Bacterial Growth
- Nutrition: Essential for growth.
- Temperature: Classified into mesophilic (25-40ºC), thermophilic (55-58ºC), and psychrophilic (below 20ºC).
- Oxygen Requirement:
- Strict aerobes: require oxygen.
- Strict anaerobes: cannot tolerate oxygen.
- Microaerophiles: require low levels of oxygen.
- Facultative anaerobes: can grow with or without oxygen.
- H-ion Concentration:
- Neutrophiles: pH 7.2-7.6.
- Acidophiles: thrive in acidic conditions.
- Alkalophiles: prefer alkaline environments.
- Moisture: Essential for protoplasm; drying is lethal.
- Osmotic Effects: Bacteria may tolerate osmotic variations due to cell wall strength.
- Radiation: X and gamma rays can be lethal.
- Mechanical Stress: High-stress conditions can cause cell lysis.
Bacterial Nutrition
- Water comprises 80% of bacterial cell weight.
- Essential nutrients include carbon, nitrogen, and inorganic salts.
- Carbon-based classification:
- Autotrophs: Synthesize own organic compounds.
- Heterotrophs: Depend on preformed organic compounds for growth.
Growth Factors
- Some bacteria require organic compounds in small amounts for growth.
- Essential factors: Required for growth.
- Accessory factors: Enhance growth but are not strictly necessary.
Basic Bacterial Techniques
- Streak Culture: Isolates single colonies using a loop on an agar plate.
- Lawn Culture: Produces uniform growth; used for antibiotic testing and vaccine preparation.
- Stroke Culture: Grows bacteria in agar slants for diagnostic tests.
- Stab Culture: Created by puncturing medium to maintain stock culture.
- Pour Plate Culture: Helps assess bacterial counts by mixing with liquid agar before solidifying.
- Spread Plate Culture: Distributes bacteria evenly across an agar surface.
Liquid Culture
- Inoculated via loops or pipettes, preferred for when large yields are necessary, such as blood cultures and sterility tests.
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