Microbiology Chapter 7: Bacterial Growth and Culturing

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Questions and Answers

Which method is specifically used to provide sufficient oxygen for obligate aerobes?

Aeration (correct)

Candle Jar

Deep-freezing

Anaerobic Jar/Chamber

What is the primary function of an anaerobic jar/chamber?

It supports the growth of obligate anaerobes. (correct)

It provides a microaerophilic environment.

It is used for the storage of bacterial cultures.

It aids in the cultivation of obligate aerobes.

What characteristic of bacterial cultures is preserved through lyophilization?

Involves the use of antifreeze agents

Requires storage at -80 ºC

Allows for long-term room temperature storage (correct)

Demands constant refrigeration

Which of the following is NOT a method of preserving bacterial cultures?

Sterilization Signup and view all the answers

Which method can identify bacteria using a seven-digit profile number derived from biochemical tests?

Analytical Profile Index (API) Signup and view all the answers

What mechanism do some bacteria use to adapt to limited nutrients?

Endospore formation Signup and view all the answers

Which of the following statements is true regarding sporulation?

It is initiated by a decrease in carbon or nitrogen levels. Signup and view all the answers

Which of the following is NOT a type of bacterial interaction?

Commensal Signup and view all the answers

What is quorum sensing primarily concerned with?

Gene expression based on cell density Signup and view all the answers

Which component is NOT part of an endospore's core structure?

Lipids Signup and view all the answers

What role does the cortex play in endospores?

Shielding against osmotic pressure Signup and view all the answers

Which of the following best describes the relationship between bacteria in a synergistic interaction?

Both organisms benefit from the relationship. Signup and view all the answers

Why do bacteria adjust their metabolism when nutrients are limited?

To maximize energy efficiency Signup and view all the answers

What stimulates the activation of specific adaptive genes in bacteria during quorum sensing?

Accumulate of inducer molecules Signup and view all the answers

What is the primary characteristic of bacteria in a biofilm?

Forming clusters that stick to each other Signup and view all the answers

What percentage of bacterial infections in humans are attributed to biofilms?

Two-thirds Signup and view all the answers

Which method involves spreading a diluted sample over the surface of an agar plate to obtain isolated colonies?

Streak Plate Method Signup and view all the answers

In what industrial context are biofilms commonly associated?

Premise plumbing corrosion Signup and view all the answers

How do bacteria within a biofilm contribute to genetic diversity?

By exchanging genetic material Signup and view all the answers

What type of culture medium encourages the growth of specific organisms while suppressing others?

Selective media Signup and view all the answers

What technique is used to prevent contamination when culturing bacteria?

Aseptic technique Signup and view all the answers

Which type of medium has an unknown chemical composition and may vary between batches?

Complex medium Signup and view all the answers

What observable characteristic is used to identify lactose fermenters on MacConkey agar?

Red colonies Signup and view all the answers

What is a consequence of bacteria growing in close proximity within a biofilm?

They release factors to kill one another Signup and view all the answers

What is one of the methods mentioned for isolating single bacterial cells?

Serial dilution Signup and view all the answers

What component in mannitol salt agar indicates fermentation by pathogenic Staphylococcus aureus?

Phenol red Signup and view all the answers

Which culture technique involves diluting and then plating samples to separate individual cells?

Pour plate method Signup and view all the answers

What is the purpose of using enrichment media?

To allow for the growth of fastidious organisms Signup and view all the answers

Which of the following correctly describes a characteristic of differential media?

Contains mannitol to test for fermentation Signup and view all the answers

Study Notes

Lecture 9: Growth and Culturing of Bacteria - 2

Lecture focuses on bacterial growth, culturing, and factors affecting growth
Chapter 7 in a Microbiology textbook
Instructor: Qiang Chen, [email protected]

Chapter Targets

Bacterial Growth and Division
Factors Affecting Bacterial Growth
Culturing Bacteria and Medium

Adaptation to Limited Nutrients

Some bacteria synthesize more enzymes to absorb and process limited nutrients
Others develop the ability to utilize different nutrients (e.g., glucose to lactose)
Many organisms optimize nutrient metabolism efficiency; avoiding wasted energy during growth
Some bacteria form endospores to adapt to nutrient scarcity

Sporulation

Endospores are formed in certain Gram-positive bacteria (Bacillus, Clostridium), and are a mechanism for survival, not reproduction
Characterized by a distinctive internal core structure comprised of RNA, protein, DNA, dipicolinic acid, and calcium ions.
A protective cortex layer surrounds this core, providing resilience against osmotic pressure.
A spore coat envelops the cortex making the endospore resistant to chemical damage
Sporulation response to environmental cues like lower carbon or nitrogen levels
Spores germinate into vegetative cells in suitable environments.
Sporulation differs from fungal spores in its formation, response signaling and role

Sporulation Cycle

Cycle alternates between vegetative (growth) and sporulation (survival) modes
Factors triggering sporulation are environmental (e.g., low nutrient levels) or metabolic signals.

Endospore Formation

An example of an important adaptation in bacteria to endure harsh conditions, such as starvation.

Factors Affecting Bacterial Growth

The topic is presented as a slide title

Bacterial Interactions

Organisms interact within various types of relationships:
- Antagonistic (competitive)
- Synergistic (cooperative)
- Symbiotic
Competition between bacteria can lead to toxin production

Quorum Sensing

Quorum: the minimum number of members required in an assembly to make proceedings valid.
Quorum sensing in bacteria: gene expression regulation in response to cell density changes.
A communication method to coordinate behavior in groups (large bacterial populations)
Signaling molecule concentration determines the expression of specific genes, influencing group behavior.
- Signaling molecules (inducers) trigger events like food digestion or biofilm growth.

Biofilms

Biofilm: a community of microorganisms where cells stick together and often attach to a surface.
Biofilm characteristics include:
- Antibiotic resistance
- Genetic exchange
- Sensing and response to other organisms in the biofilm

Biofilms in medicine, industry, and aquaculture

Two-thirds of infections involve biofilm formation in humans
Biofilms create antimicrobial tolerance and evade immune systems
Biofilms cause premise plumbing corrosion.
Biofilms affect aquaculture environments.

Technological Approaches to Combat Biofilms

Approaches to overcome biofilm issues are discussed in this section:
Surface modification
Nanoparticles or small-molecule agents
Physical removal

Biofilms in Wound Healing

Topical antimicrobial epoxy-tiglianes from the blushwood tree induce biofilm disruption, wound healing in acute and chronic skin wounds.

Alcanivorax borkumensis Biofilms

This bacterium forms biofilms around oil droplets, but the exact role in oil degradation is discussed.
A morphological shift facilitates efficient oil degradation through interfacial tubulation.
The biofilm development leads to interfacial defects in the biofilm that improve biodegradation efficiency
Microbes modify the oil droplets to speed the process of biodegradation.

Culturing Bacteria

Not all bacteria in natural environments can be grown in a laboratory setting.

Types of Culture Media

Liquid media (broth) are common for growth
Solid media (agar, petri dishes, slant tubes).
Semi-solid media (0.5% agar) are useful in various applications.

Culture Media Composition

Defined synthetic media: composition is precisely known
Complex media (chemically unspecified): composition varies, and isn't precisely known

Culture Media Purposes

Selective media encourage a specific microorganism, while suppressing others.
Differential media lead to observable changes (color, pH) based on particular characteristics.
Enrichment media allow a target organism to thrive.

Controlling Oxygen Content

Aeration sustains organisms that require oxygen
Candle jars support microaerophilic growth conditions
Anaerobic jars/chambers eliminate oxygen for anaerobic species cultivation

Bacterial Identification

Gram staining is a method to differentiate bacterial species based on cell wall structure.
Morphology is the analysis of cell characteristics (shape, size).
Oxygen requirement (aerobes, anaerobes, facultative anaerobes) are essential classifications for bacterial identification.
Biochemical tests reveal additional traits.

Methods of Performing Multiple Diagnostic Tests

Analytical Profile Index (API): A method to identify bacteria and yeast based on biochemical tests.

Preserving Bacterial Cultures

Refrigeration: short-term (hours or days) storage
Deep-freezing: long-term storage after a freezing step
Lyophilization (freeze-drying): long-term, stable storage after freezing a liquid sample, and removing the water.

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Description

This quiz explores bacterial growth, factors affecting culturing, and the adaptation mechanisms of bacteria to limited nutrients. It covers key concepts such as sporulation and nutrient metabolism, focusing on the specifics outlined in Chapter 7 of a Microbiology textbook.