Exam 3 study guide lab

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Questions and Answers

What role do endospores play in bacterial resistance to disinfectants?

They produce enzymes to neutralize disinfectants.

They facilitate the absorption of disinfectants.

They are thick-walled structures that allow survival in extreme conditions. (correct)

They help bacteria multiply rapidly.

How do biofilms contribute to bacterial resistance against disinfectants?

They encase bacteria in a protective matrix that hinders disinfectant penetration. (correct)

They increase the metabolic rate of bacteria.

They enhance the growth rate of bacteria.

They provide nutrients to the bacteria.

What is the function of efflux pumps in bacteria?

To produce metabolic waste.

To facilitate cell division.

To absorb nutrients from the environment.

To pump out toxic substances and reduce disinfectant effectiveness. (correct)

Which characteristic of gram-negative bacteria makes them more resistant to disinfectants compared to gram-positive bacteria?

They possess an additional outer membrane that acts as a barrier. Signup and view all the answers

What is the main function of antibiotics in treating bacterial infections?

To specifically target bacterial structures or functions crucial for survival. Signup and view all the answers

What does the Kirby-Bauer disk diffusion test evaluate?

The effectiveness of antibiotics on a bacterial species. Signup and view all the answers

What indicates that a bacterial species is sensitive to an antibiotic in the Kirby-Bauer test?

Large zones of inhibition around the antibiotic disks. Signup and view all the answers

Why are antibiotics ineffective against viruses?

Viruses do not have cellular structures that antibiotics target. Signup and view all the answers

What change indicates a positive result for mannitol fermentation on MSA?

The agar turns yellow Signup and view all the answers

Which pathogenic species is primarily identified using mannitol salt agar (MSA)?

Staphylococcus aureus Signup and view all the answers

What distinguishes vertical gene transfer from horizontal gene transfer in bacteria?

Vertical transfer occurs during reproduction Signup and view all the answers

Which process involves the direct transfer of genetic material between bacteria through cell contact?

Conjugation Signup and view all the answers

In which mechanism do bacteria take up free DNA from the environment?

Transformation Signup and view all the answers

What is a characteristic of transduction in bacteria?

Transfers DNA via a bacteriophage Signup and view all the answers

Which statement correctly compares transformation and transduction?

Both can integrate DNA into the bacterial genome Signup and view all the answers

What is the primary outcome of horizontal gene transfer in bacteria?

Acquisition of new traits Signup and view all the answers

What is indicated by a positive result in the Snyder test?

The medium turns from green to yellow due to high acid production. Signup and view all the answers

Which type of hemolysis is characterized by complete breakdown of red blood cells, creating a clear zone around colonies?

Beta hemolysis Signup and view all the answers

What differentiates alpha hemolysis from gamma hemolysis on a blood agar plate?

Alpha hemolysis results in partial lysis, while gamma hemolysis shows no lysis of red blood cells. Signup and view all the answers

What is the primary purpose of Mannitol Salt Agar (MSA)?

To select for halo tolerant bacteria and differentiate based on mannitol fermentation. Signup and view all the answers

What visual change indicates mannitol fermentation on Mannitol Salt Agar?

The agar turns yellow. Signup and view all the answers

Which of the following is NOT a characteristic of blood agar?

It is selective for specific bacterial species. Signup and view all the answers

What does the pH indicator bromocresol green in Snyder test medium indicate?

Acid production by bacteria. Signup and view all the answers

How can you classify Enterococcus faecalis in terms of hemolysis?

Gamma hemolytic. Signup and view all the answers

What is the expected outcome for the +pGLO cells when grown on LB + Ampicillin + Arabinose?

Cells will grow and glow due to GFP expression. Signup and view all the answers

Why do pGLO cells grow normally on LB medium?

They do not require plasmid for growth. Signup and view all the answers

Which statement accurately describes the impact of arabinose on transformed cells?

Arabinose induces the expression of the GFP gene. Signup and view all the answers

What results would you expect for +pGLO cells in LB + Ampicillin?

Cells will grow but will not glow due to lack of arabinose. Signup and view all the answers

What defines a mutation?

A spontaneous change in DNA sequence. Signup and view all the answers

How can mutations be beneficial to an organism?

By providing new traits that help with adaptation. Signup and view all the answers

Which type of mutation is typically regarded as neutral?

Mutations that alter the sequence but do not change the protein. Signup and view all the answers

What role do physical mutagens like high-energy light play in mutations?

They can induce changes in the DNA sequence. Signup and view all the answers

What does a larger zone of inhibition suggest about bacteria's sensitivity to an antibiotic?

The bacteria are sensitive to the antibiotic. Signup and view all the answers

How does the Minimum Inhibitory Concentration (MIC) relate to the Kirby-Bauer test?

The size of the zone of inhibition correlates with MIC values. Signup and view all the answers

What does a small or no zone of inhibition indicate about a bacterium's resistance?

The bacteria are resistant and the antibiotic will likely not be effective. Signup and view all the answers

What characterizes a bactericidal antibiotic in the Kirby-Bauer test?

It creates a clear and distinct zone of inhibition. Signup and view all the answers

Why is the Minimum Inhibitory Concentration (MIC) not used directly as medication?

The prescribed doses are usually higher than the MIC. Signup and view all the answers

What does an intermediate zone of inhibition suggest about antibiotic effectiveness?

Higher doses of the antibiotic may be required for effectiveness. Signup and view all the answers

How can one differentiate between bacteriostatic and bactericidal antibiotics using the Kirby-Bauer test?

Bacteriostatic antibiotics may show regrowth if subcultured. Signup and view all the answers

What is the focus of epidemiology in public health?

To analyze the patterns and determinants of health and disease. Signup and view all the answers

Study Notes

Bacterial Structures for Disinfectant Resistance

Endospores: Thick-walled structures enabling bacteria like Bacillus and Clostridium to survive extreme conditions, including disinfectants.
Biofilms: Bacterial communities encased in a protective matrix that adheres to surfaces, making disinfectant penetration difficult.
Outer Membrane in Gram-Negative Bacteria: Provides an extra barrier against many disinfectants, increasing their resistance compared to Gram-positive bacteria.
Efflux Pumps: Protein channels actively pumping out toxins, including disinfectants, from bacterial cells, reducing the disinfectant's effectiveness.

Antibiotic Action

Antibiotics: Chemicals often produced by microorganisms that inhibit bacterial and fungal growth, sometimes killing them.
Target Specificity: Antibiotics target specific bacterial structures or functions essential for survival, like cell wall synthesis or protein production, not found in human cells.
Selective Toxicity: Enables antibiotics to treat bacterial infections without harming the host.
Ineffectiveness against Viruses: Antibiotics are typically ineffective against viruses.

Kirby-Bauer Disk Diffusion Test

Method: Evaluates antibiotic effectiveness on bacterial species by measuring antibiotic diffusion and bacteria growth on agar plates.
Steps:
- Spread a standardized bacterial suspension evenly on an agar plate.
- Place antibiotic impregnated disks on the agar surface.
- Incubate the plate to allow bacteria growth and antibiotic diffusion.
Analysis:
- Zone of Inhibition: Clear areas surrounding the disks where bacteria did not grow, indicating antibiotic effectiveness.
- Zone of Inhibition Size: Represents bacterial sensitivity to the antibiotic (Larger zone = more sensitive).
- Minimum Inhibitory Concentration (MIC): Lowest antibiotic concentration inhibiting bacterial growth (Not directly measured, but inferred from zone size).

Sensitivity and Resistance

Sensitive (S): A large zone of inhibition indicates susceptibility and effectiveness at standard doses.
Intermediate (I): A medium-sized zone suggests moderate sensitivity where higher doses may be needed.
Resistant (R): A small or no zone indicates resistance, making the antibiotic likely ineffective.

Bactericidal vs. Bacteriostatic Antibiotics

Bactericidal Antibiotics: Kill bacteria, resulting in a clear zone of inhibition.
Bacteriostatic Antibiotics: Inhibit bacterial growth but may not kill them, potentially showing a less distinct zone or regrowth upon subculturing.

Epidemiology and Disease

Epidemiology: The study of disease distribution, patterns, and determinants within populations.
Snyder Test Medium: Detects acid-producing bacteria, particularly Lactobacillus species associated with cavities.
- Positive Result: Medium turns yellow due to acid production, indicating higher caries susceptibility.
- Negative Result: Medium remains green, indicating lower acid production and less susceptibility.

Blood Agar Plate

Description: A growth medium containing nutrients and sheep's blood, used to observe hemolytic properties of bacteria.
Differential, Not Selective: Differentiates bacteria based on red blood cell lysis (hemolysis), not selective for specific bacteria.

Hemolysis

Definition: The breakdown of red blood cells by bacterial enzymes.
Types:
- Alpha Hemolysis: Partial hemolysis, causing a greenish or brownish discoloration around colonies. (Example: Streptococcus pneumoniae)
- Beta Hemolysis: Complete hemolysis producing a clear, transparent zone around colonies. (Example: Streptococcus pyogenes)
- Gamma Hemolysis: No hemolysis, with no change in agar color around colonies. (Example: Enterococcus faecalis)

MSA (Mannitol Salt Agar)

Selective and Differential:
- Selective: Selects for halotolerant bacteria like Staphylococcus species due to high salt concentration (7.5% NaCl).
- Differential: Differentiates based on mannitol fermentation, indicated by a color change from red to yellow due to acid production.
Positive Result: Medium turns yellow, indicating mannitol fermentation.
Negative Result: Medium remains red.
Identification: Primarily used to identify Staphylococcus aureus, which ferments mannitol, from other non-fermenting Staphylococcus species like Staphylococcus epidermidis.

Vertical and Horizontal Gene Transfer

Vertical Gene Transfer: Transmission of genetic material from parent to offspring during reproduction, occurring through binary fission in bacteria.
Horizontal Gene Transfer: Transfer of genetic material between unrelated bacterial cells, enabling acquisition of new traits independently of reproduction.

Horizontal Gene Transfer Types

Conjugation: Direct cell-to-cell contact for transfer of genetic material, often involving plasmids.
Transformation: Bacteria take up free DNA from the environment, potentially integrating it into their genome or as a plasmid.
Transduction: Bacteriophages (viruses) transfer genetic material between bacteria.

pGLO Transformation Experiment

Arabinose Role: Induces GFP expression in transformed cells, causing them to glow under UV light.

pGLO Expected Results

LB (Luria broth) only:
- -pGLO: Growth expected without glowing; no plasmid for ampicillin resistance or GFP expression.
- +pGLO: Growth expected without glowing; transformed cells grow but GFP expression is not induced.
LB + Ampicillin:
- -pGLO: No growth expected; lacking ampicillin resistance.
- +pGLO: Growth expected without glowing; ampicillin resistance conferred by the plasmid, but no GFP expression.
LB + Ampicillin + arabinose:
- -pGLO: No growth expected; no ampicillin resistance.
- +pGLO: Growth expected with glowing; ampicillin resistance and arabinose-induced GFP expression.

Mutations

Definition: Changes in DNA sequence that can alter genetic information.
Causes: Occur spontaneously or be induced by environmental factors.
Effects: Good (beneficial traits), bad (harmful effects), or neutral (no noticeable effect).
Physical Mutagens: High-energy light can cause DNA mutations.

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Description

Explore the fascinating world of bacteria and their strategies for surviving disinfectants and antibiotics. This quiz covers essential topics like endospores, biofilms, and the mechanisms of antibiotic action. Test your knowledge on how bacteria resist treatment and the specific targets of antibiotics.