Lesson 3: Microbial Nutrition

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Questions and Answers

Which type of media contains unknown ingredients?

Transport media

Complex media (correct)

Defined media

Simple media

What characterizes simple media?

They are used for non-fastidious bacteria. (correct)

They contain defined ingredients.

They are specifically for fastidious microbes.

They have undefined nutritional components.

Which type of media would you use to identify lactose fermentation?

MacConkey agar (correct)

Blood agar

Nutrient broth

Eosin Methylene Blue

What type of medium is intended for fastidious microbes?

Enriched medium Signup and view all the answers

What distinguishes selective media from other types of media?

Inhibits the growth of some organisms. Signup and view all the answers

What is the primary function of transport media?

To stabilize delicate organisms during transport. Signup and view all the answers

Which of the following is an example of anaerobic media?

Robertson’s cooked meat medium Signup and view all the answers

What is the purpose of a stab culture?

To study oxygen requirements. Signup and view all the answers

What is the main purpose of the direct microscopic count method?

To extrapolate the number of bacteria from a known volume Signup and view all the answers

Which method involves forcing a microbial suspension through a small hole to measure electrical resistance?

Electronic Enumeration of Cells Signup and view all the answers

In the Plate Count Method, what is the standard volume of culture typically pipetted into the Petri plate?

0.1–1.0 ml Signup and view all the answers

What does the turbidimetric method measure in a bacterial culture?

The light-scattering effect due to bacterial growth Signup and view all the answers

Which technique involves trapping bacteria on a membrane filter to estimate bacterial numbers in aquatic samples?

Membrane Filter Technique Signup and view all the answers

In the determination of dry weight method, what is measured as a direct result of microbial growth?

Weight of cells Signup and view all the answers

What characteristic change in growth medium is detected by measuring specific chemical changes?

Production of acid and gas by bacteria Signup and view all the answers

Which method is used to spread a diluted bacterial culture over an agar plate?

Spread-plate Method Signup and view all the answers

During which phase does the number of dividing cells equal the number of dying cells?

Stationary phase Signup and view all the answers

What is a characteristic of synchronous growth?

All cells are in the same growth stage Signup and view all the answers

Which of the following best describes diauxic growth?

Growth phase involving two separate sugars Signup and view all the answers

What is the primary function of the chemostat in continuous culture?

To achieve a steady-state environment for microbial growth Signup and view all the answers

What does the generation time of microbial cells represent?

Time required for cells to double in number Signup and view all the answers

Which method specifically counts only viable cells?

Viable count Signup and view all the answers

What characterizes the death phase in microbial growth?

Exponential decrease in the number of living cells Signup and view all the answers

What is the definition of colony-forming units (CFU)?

Units representing viable counts from a solid media Signup and view all the answers

What do photolithotrophic autotrophs utilize for their energy and carbon sources?

Light and inorganic compounds Signup and view all the answers

Which of the following nitrogen requirements is incorrect for certain autotrophs and cyanobacteria?

They must take in nitrogen from atmosphere. Signup and view all the answers

In which class of bacteria does growth occur only in the presence of oxygen?

Obligate aerobes Signup and view all the answers

How do psychrophiles differ from thermophiles regarding their temperature range?

Psychrophiles grow optimally at temperatures of 15 degrees C or lower. Signup and view all the answers

What is a characteristic feature of defined media compared to complex media?

Defined media has an exact composition known in qualitative and quantitative terms. Signup and view all the answers

Which nutrient is used by all microbes and is found in essential cellular components?

Phosphorus Signup and view all the answers

What type of medium is primarily used for checking motility in microorganisms?

Semi-solid medium Signup and view all the answers

What factor is deemed most important regarding the growth of microorganisms?

Temperature range Signup and view all the answers

Which statement about facultative anaerobes is true?

They can grow with or without oxygen. Signup and view all the answers

What is the optimal growth temperature range for mesophiles?

25 - 40 degrees C Signup and view all the answers

What is the primary purpose of the pour plate method?

To estimate viable bacterial counts in a suspension Signup and view all the answers

Which culture method is primarily used for antibiotic sensitivity testing?

Lawn culture Signup and view all the answers

What does colony morphology help to determine?

If a culture is contaminated or pure Signup and view all the answers

What is a significant drawback of using the pour plate method?

It can only be used with heat-stable bacteria Signup and view all the answers

In which phase of microbial growth are bacteria metabolically active but not dividing?

Lag phase Signup and view all the answers

What best describes the streak plate technique?

A technique for isolating pure cultures Signup and view all the answers

What is the purpose of using agar in microbial culture?

To solidify the culture media Signup and view all the answers

What does aseptic technique help prevent during microbial culture?

Contamination from undesired microorganisms Signup and view all the answers

Study Notes

Microbial Nutrition and Growth Requirements

Photolithotrophs: Organisms that use light and inorganic compounds for energy and carbon.
Chemoorganotrophic heterotrophs: Organisms that obtain energy from organic compounds.

Essential Nutrients

Nitrogen:
- Crucial for amino acids, purines, and lipids.
- Utilized by autotrophs and some microbes by reducing nitrate to ammonia.
Phosphorus:
- Present in nucleic acids, ATP, and phospholipids.
- Required by all microbes.
Sulfur:
- Needed for amino acids like cysteine and methionine.
- Some microbes need reduced sulfur forms like cysteine.

Growth Factors

Vital for microbes lacking specific enzymatic pathways.
Includes:
- Amino acids: Essential for protein synthesis.
- Purines & Pyrimidines: Required for nucleic acid synthesis.
- Vitamins: Act as co-factors in enzymes, needed in small amounts.

Gaseous Requirements

Aerobic Bacteria: Require oxygen for growth (e.g., Pseudomonas aeruginosa).
Anaerobic Bacteria: Thrive in absence of oxygen (e.g., Clostridium tetani).
- Obligate anaerobes: Die in oxygen.
- Facultative anaerobes: Can use oxygen or grow via fermentation.
Microaerophilic Bacteria: Prefer low oxygen concentrations.

Temperature Requirements

Temperature affects microbial growth significantly; optimal temperatures vary.
- Psychrophiles: Grow at 15°C or lower.
- Psychrotrophs: Thrive at 20-30°C.
- Mesophiles: Optimal growth between 25-40°C.
- Thermophiles: Prefer 55-60°C.

Other Growth Requirements

Include moisture, pH, light exposure, osmotic balance, and mechanical stress.

Culture Media Types

Defined Media: Know exact composition; made from pure chemicals.
Complex Media: Made from digests of biological materials like yeast and meat extracts.
Consistency:
- Solid Media: Typically contains 2% agar for colony observations.
- Liquid Media: No agar, used for growing cultures.
- Semi-solid Media: Used to examine motility.
Nutritional Type:
- Simple Media: Nutrient-rich for non-fastidious microorganisms.
- Enriched Media: Contains special nutrients for fastidious microbes (e.g., blood agar).
Functional:
- Selective Media: Prevent growth of unwanted bacteria.
- Differential Media: Contains indicators to reveal metabolic reactions (e.g., MacConkey agar).

Isolation of Pure Cultures

Essential for species characterization and identification.
Methods include:
- Streak Culture: Isolates colonies from clinical samples.
- Pour Plate Method: Estimates viable cell count in a sample.

Agar and Colony Morphology

Agar solidifies media, allowing growth of colonies for study.
Colony characteristics help identify purity and contamination levels.

Microbial Growth Phases

Lag Phase: Metabolic activity without division.
Log Phase: Rapid exponential growth.
Stationary Phase: Balance between dividing and dying cells.
Death Phase: Decline in viable cell numbers.

Growth Measurement Techniques

Microscopic Cell Count: Direct counting under microscope.
Viable Count: Bacteria counted post-culture on solid media.
Turbidimetric Methods: Measures light blockage by bacterial growth in media.

Diauxic Growth

Growth pattern when microbes metabolize two sugars sequentially.

Continuous Culture Techniques

Chemostats maintain steady-state growth by continuous nutrient renewal.

Key Measurement Techniques

Methods include direct microscopic counts, electronic enumeration, and various plate counting methods.

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Description

Explore the essential elements for autotrophic and heterotrophic organisms in this quiz. Topics include nitrogen, phosphorus, and sulfur along with their roles in synthesizing vital biomolecules. Test your knowledge on the biochemical needs of various microbes and their metabolic processes.