Ch 9

What is bacterial growth?

Bacterial growth refers to the increase in the number of bacterial cells in a population over time, measured through changes in cell number or cell mass.

What is a colony?

A colony is a visible mass of microorganisms, often bacteria, that are derived from a single cell, observed on solid growth media.

What is binary fission?

Binary fission is the primary method of asexual reproduction in bacteria where a single cell divides into two identical daughter cells.

Describe the events that occur during binary fission.

The bacterial chromosome is replicated. The cell elongates. The cell membrane and wall grow inward to form a septum, dividing the cell into two. The daughter cells separate, resulting in two genetically identical cells.

What is logarithmic or exponential growth?

Logarithmic growth describes a phase where the number of cells in a population doubles at regular intervals, resulting in rapid biomass increase, modeled as $N(t) = N_0 e^{rt}$.

What is a growth curve?

A growth curve is a graphical representation of the growth of a microbial population over time, displaying different phases of growth.

What are the 4 components of a microbial growth curve?

1. Lag Phase: Initial adaptation phase. 2. Log Phase: Exponential growth occurs. 3. Stationary Phase: Growth rate stabilizes due to limited resources. 4. Death Phase: Decline in the number of viable cells.

During which phase are populations more susceptible to antibiotics?

During the log phase, when cells are actively dividing and are more susceptible to antibiotics targeting cell wall synthesis or DNA replication.

When is the Gram stain most effective?

Performing the Gram stain is most effective during the log phase when cells are actively dividing.

What is a biofilm?

Biofilms arise when microorganisms adhere to surfaces and each other, creating a complex community encased in a protective extracellular matrix.

How can biofilms impact human health?

Biofilms can enhance bacterial resistance to antibiotics and immune responses, leading to persistent infections and complications.

Why is measuring bacterial growth important?

Measuring bacterial growth is crucial for understanding microbial metabolism, disease progression, and the effectiveness of antibiotics.

What is a common method for measuring microbial growth?

A common indirect method is optical density (OD) measurements, assessing light transmission through a culture.

What are the nutrients used for in microbial growth?

Nutrients are sources of energy and building blocks for biosynthesis, enabling microbial cell growth, reproduction, and metabolism.

What happens when microbes acquire nutrients from living hosts?

These microbes are categorized as parasites, potentially causing harm while deriving nutrients.

Define an autotroph.

An organism that produces its own food, typically through photosynthesis or chemosynthesis.

Define a heterotroph.

An organism that obtains food by consuming other organisms or organic matter.

Define a chemotroph.

An organism that obtains energy by oxidizing chemical compounds.

Define a phototroph.

An organism that derives energy from light.

Define a photoautotroph.

An organism that uses light energy to convert carbon dioxide into organic compounds.

Define a photoheterotroph.

An organism that uses light for energy but must obtain carbon from organic sources.

Define a chemoautotroph.

An organism that derives energy from inorganic compounds and uses carbon dioxide as its carbon source.

Contrast aerobes and obligate anaerobes.

Aerobes require oxygen for growth, while obligate anaerobes cannot survive in the presence of oxygen.

What are the reactive forms of oxygen dangerous for obligate anaerobes?

Reactive forms of oxygen like superoxide and hydrogen peroxide can damage cellular components, leading to cell death.

Define minimum growth temperature.

The lowest temperature at which an organism can grow and reproduce.

Define maximum growth temperature.

The highest temperature at which an organism can grow and reproduce.

Define optimum growth temperature.

The temperature at which an organism grows best.

What is a psychrophile?

An organism that grows best at temperatures below 15°C; important in cold environments.

What is a mesophile?

An organism that grows best between 20°C-45°C; most pathogenic bacteria fall into this category.

What is a thermophile?

An organism that thrives at higher temperatures (optimal at 45°C and above) and is important in hot environments.

What is an acidophile?

An organism that tolerates acidic conditions.

What happens to a microbe in a hypertonic environment?

The microbe loses water, undergoes plasmolysis, and may die.

What is a barophile?

An organism that thrives at high pressures, found in deep-sea environments.

What is a selective medium?

A culture medium that favors the growth of certain microorganisms while inhibiting others.

What is a differential medium?

A medium that allows differentiation between organisms based on their biochemical reactions.

Explain how refrigeration preserves cultures.

Refrigeration slows metabolic activity and prolongs the viability of cultures for short-term storage.

Explain how deep-freezing preserves cultures.

Deep-freezing cools cultures to very low temperatures (below -70°C), halting metabolic processes for long-term storage.

What is lyophilization?

Lyophilization is freeze-drying that preserves cultures in a dry form, which can be rehydrated later.