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Bacterial Growth, Enumeration, and Culture Media

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Termini in questo insieme (20)

  • What is bacterial growth?

    Bacterial growth refers to the increase in the number of bacterial cells, not the size of individual cells.

  • What are the phases of bacterial growth in a batch culture?

    The phases are lag phase, log (exponential) phase, stationary phase, and death phase.

  • What happens during the lag phase?

    Cells adapt to new conditions, synthesize enzymes, but do not divide significantly.

  • Describe the log phase of bacterial growth.

    Cells divide at a constant and rapid rate, leading to exponential increase in cell number.

  • What characterizes the stationary phase?

    Growth rate slows and stabilizes as nutrients deplete and waste accumulates; cell division equals cell death.

  • What occurs during the death phase?

    Cells die at an exponential rate due to lack of nutrients and toxic conditions.

  • What is bacterial enumeration?

    Bacterial enumeration is the process of counting the number of bacteria in a sample.

  • Name two common methods of bacterial enumeration.

    Plate count method and direct microscopic count.

  • What is the plate count method?

    It involves spreading a diluted sample on agar plates and counting colony-forming units (CFUs) after incubation.

  • What does one colony-forming unit (CFU) represent?

    One CFU represents one viable bacterial cell or a group of cells that formed a colony.

  • What is the purpose of serial dilution in bacterial enumeration?

    To reduce bacterial concentration to a countable range on agar plates.

  • What is direct microscopic count?

    Counting bacteria directly under a microscope using a specialized counting chamber.

  • What are culture media?

    Culture media are nutrient solutions or gels used to grow microorganisms in the lab.

  • What are the main types of culture media based on physical state?

    Liquid (broth), solid (agar), and semi-solid media.

  • What is the difference between selective and differential media?

    Selective media inhibit growth of some microbes; differential media distinguish microbes based on biochemical traits.

  • Give an example of selective media.

    MacConkey agar, which selects for Gram-negative bacteria.

  • Give an example of differential media.

    Blood agar, which differentiates bacteria based on hemolysis patterns.

  • Why is agar used in solid media?

    Agar is a solidifying agent that is not metabolized by most bacteria and remains solid at incubation temperatures.

  • What factors affect bacterial growth in culture media?

    Temperature, pH, oxygen availability, nutrient composition, and moisture.

  • What is the generation time in bacterial growth?

    The time required for a bacterial population to double during the log phase.