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Microbial Growth - Microbiology

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  • Psychrophiles

    Psychrophiles are microbes that grow optimally at about 15º C, preferring cold environments.

  • Mesophiles

    Mesophiles grow best at moderate temperatures, typically between 25º and 40º C.

  • Thermophiles

    Thermophiles grow best at high temperatures, usually between 50º and 60º C.

  • pH range for most bacterial growth

    Most bacteria grow best at a pH between 6.5 and 7.5.

  • Hypertonic solution effect on microbes

    In a hypertonic solution, microbes undergo plasmolysis due to water loss.

  • Halophiles

    Halophiles tolerate high salt concentrations; extreme halophiles require very high salt, obligate halophiles need salt to grow, and facultative halophiles tolerate but do not require salt.

  • Obligate aerobes

    Obligate aerobes require oxygen for growth.

  • Facultative anaerobes

    Facultative anaerobes can grow with or without oxygen but grow better with oxygen.

  • Obligate anaerobes

    Obligate anaerobes cannot tolerate oxygen and grow only in its absence.

  • Biofilm formation

    Bacteria attach to solid surfaces and accumulate as biofilms; quorum sensing allows grouping, and water currents help nutrient access and waste removal.

  • Selective media

    Selective media suppress unwanted microbes and encourage growth of desired microbes using inhibitory substances like salts or dyes.

  • Differential media

    Differential media distinguish colonies of different microbes by visible changes, such as hemolysis on blood agar.

  • MacConkey agar

    MacConkey agar is selective for gram-negative bacilli and differentiates lactose fermenters (dark pink colonies) from nonfermenters.

  • Mannitol Salt Agar (MSA)

    MSA selects for Staphylococcus due to high salt; S. aureus ferments mannitol turning colonies yellow, while S. epidermidis does not.

  • Anaerobic jar purpose

    Anaerobic jars create oxygen-free environments for growing obligate anaerobes using reducing agents.

  • Pure culture

    A pure culture is a population of cells derived from a single cell, obtained by the streak plate method.

  • Binary fission

    Binary fission is the process by which bacteria reproduce by dividing into two identical daughter cells.

  • Generation time

    Generation time is the time it takes for a bacterial population to double in number.

  • Phases of bacterial growth

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

  • Direct methods of measuring bacterial growth

    Direct methods include plate counts, filtration, direct microscopic count, and most probable number.

  • Indirect methods of measuring bacterial growth

    Indirect methods include measuring turbidity, metabolic activity, and dry weight of bacterial cultures.