Microbial Nutrition and Growth - Practice Flashcards

A set of practice flashcards covering key concepts from microbial nutrition, growth, culture methods, and lab techniques described in the lecture notes.

What is binary fission and what type of reproduction is it?

An asexual cell division in which one bacterial cell splits into two; it is a primitive form of growth that does not involve spindle fibers.

What is generation time (doubling time)?

The time required for a complete fission cycle; under favorable conditions, doubling occurs at a constant rate, typically about 30–60 minutes (can be as short as 10–12 minutes).

What does the formula Nf = Ni (2)^g describe?

Final population size after g generations, where Ni is the initial population; growth is exponential with each generation doubling the count.

Name the four main phases of the bacterial growth curve.

Lag phase, Log (exponential) phase, Stationary phase, Death phase.

Describe the Lag phase.

Newly inoculated cells adjust, enlarge, and synthesize components; little to no cell division occurs.

Describe the Log (Exponential) phase.

Cells divide at the maximum rate given abundant nutrients and favorable conditions; population increases rapidly.

Describe the Stationary phase.

Growth rate equals death rate due to nutrient depletion and waste accumulation; endospores may begin to form in this phase.

Describe the Death phase.

Cellular activity declines; deaths exceed new cells; endospores may be released.

What is meant by plate counts and CFUs?

Estimating viable cells by counting colonies on plates; typically 25–250 colonies (colony-forming units, CFUs) are counted for accuracy.

What are culture media and their main types?

Substances used to grow microbes; types include synthetic/defined, complex; selective, differential, and transport media.

What is a synthetic (defined) medium?

A medium with precisely known chemical composition.

What is a complex medium?

A medium containing undefined components such as beef extract, yeast extract, or blood.

What is selective medium?

Medium that inhibits some organisms to favor growth of a particular microbe.

What is differential medium?

Medium that allows distinguishing organisms based on metabolic differences (e.g., different colony colors or halos).

What is Mannitol Salt Agar (MSA) used for?

A selective and differential medium: high salt inhibits many organisms; those that ferment mannitol cause a color change, often used for staphylococci.

What is blood agar used for in differential testing?

Differentiates bacteria by hemolysis types: beta-hemolysis (clear), alpha-hemolysis (greenish), gamma-hemolysis (no hemolysis).

What are the main oxygen requirement categories for microbes?

Obligate aerobes, obligate anaerobes, facultative anaerobes, aerotolerant anaerobes, microaerophiles.

What are the four toxic forms of oxygen?

Singlet oxygen, superoxide radicals, peroxide (hydrogen peroxide) anion, and hydroxyl radical.

How can researchers meet oxygen requirements in the lab?

Using Thioglycollate broth, candle jars, anaerobic jars, gas-packs, or gas mixtures to create reduced- or specific-oxygen environments.

What is Thioglycollate broth used for?

A growth medium with reducing agents that creates an oxygen gradient, facilitating growth of aerobes and anaerobes as appropriate.

What does the oxygen-growth table (obligate aerobes, facultative anaerobes, etc.) illustrate?

Different organisms show characteristic growth patterns depending on the presence or absence of oxygen and their enzymatic defenses (e.g., catalase, SOD).

What are the main temperature categories for microbes?

Psychrophiles, psychrotrophs, mesophiles, thermophiles, hyperthermophiles.

What are acidophiles, neutrophiles, and alkalinophiles?

Acidophiles: grow best at pH 1–5.4; neutrophiles: around neutral pH (roughly 5.4–8.5); alkalinophiles: pH 7–11.5.

What is osmotic pressure and how do halophiles relate to it?

Hypertonic environments (high solute) cause plasmolysis; extreme halophiles require high salt; facultative halophiles tolerate high osmotic pressure.

What are transport media used for?

Used to rapidly transport clinical specimens and protect personnel from infection while preventing contamination.

How are cultures preserved long-term?

Refrigeration for short-term storage; deep-freezing (-50° to -95°C) for years; lyophilization (freeze-drying) (-54° to -72°C, vacuum dehydration) for decades.

What are biosafety levels (BSL) and their progression?

BSL-1: basic precautions; BSL-2: lab coat, gloves, eye protection; BSL-3: biosafety cabinets; BSL-4: sealed, negative pressure with highly controlled exhaust.

What is an inoculum in culturing?

The sample introduced into a medium that initiates culture growth.

What is the difference between streak plates and pour plates?

Streak plates isolate single colonies by spreading a sample on a solid surface; pour plates mix a liquid sample with molten agar before pouring into plates for colony growth within the agar.

What is the role of endospores in growth phases?

Endospores may form during the stationary phase as a survival mechanism and can be released from parent cells.

What is a chemically defined medium example for chemoheterotrophs like E. coli?

A defined medium with known amounts of glucose, ammonium phosphate, NaCl, MgSO4, K2HPO4, and water (precise composition).

What is a common example of a differential medium for hemolysis testing?

Blood agar; distinguishes bacteria by their hemolytic activity (beta, alpha, gamma).

How is growth measured in lab to assess population changes?

By plating samples and counting colonies (CFUs) after incubation; used to estimate viable cell numbers over time.

What is the practical take-home point about growth curves?

Be able to draw and describe the phases of the bacterial growth curve and understand how growth factors affect microbial growth.