Chemical Control of Growth: Labs 18-19

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Questions and Answers

What does a larger diameter of the zone of inhibition indicate about an antibiotic?

The antibiotic is ineffective against the bacteria.

The antibiotic is more effective against the bacteria. (correct)

The response is due to the concentration of the antibiotic being too high.

The bacteria are resistant to the antibiotic.

What is the purpose of measuring the disk diameter for antibiotics with no zone of influence?

To identify the specific bacterial strain.

To determine the overall bacterial resistance level.

To compare with the sensitivity reference table. (correct)

To evaluate the diffusion rate of the antibiotic.

Which of the following terms describes a bacterium that exhibits a zone of inhibition of 15 mm?

Resistant to the antibiotic

Intermediate sensitivity to the antibiotic (correct)

Sensitive to the antibiotic

Highly resistant to the antibiotic

What does the abbreviation 'S' indicate in the context of antibiotic resistance testing?

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

How does antibiotic diffusion into agar correlate with its effectiveness?

Effects of the antibiotic diminish with increased distance from the disk. Signup and view all the answers

What does the Kirby-Bauer sensitivity test primarily evaluate?

The effectiveness of antibiotics against specific bacterial species. Signup and view all the answers

Which factor could contribute to a bacterial species being more resistant to disinfectants?

Presence of protective biofilm layers. Signup and view all the answers

What is typically included in a reference table when comparing antibiotic disk diffusion measurements?

Standardized measurements for interpreting bacterial response. Signup and view all the answers

What is the purpose of using an alcohol pad during the degerming process?

To reduce the microbial load before sampling Signup and view all the answers

What does the term 'Zone of Inhibition' refer to in the Kirby-Bauer Test?

The area of inhibited growth around an antibiotic disk Signup and view all the answers

Why is Mueller-Hinton agar used in the Kirby-Bauer Test?

To ensure consistent diffusion of antibiotics Signup and view all the answers

Which of the following would NOT be a typical action taken when placing antibiotic disks on the agar plate?

Pressing down hard on the disks to ensure they stay in place Signup and view all the answers

What characteristic of antibiotics makes them effective against prokaryotes or fungi?

They target biological structures unique to these organisms Signup and view all the answers

Which method is used for evaluating antimicrobials in the Kirby-Bauer Test?

Diffusion of antibiotics from a disk into agar Signup and view all the answers

What does Minimum Inhibitory Concentration (MIC) refer to?

Minimum effective concentration of an antibiotic to inhibit growth Signup and view all the answers

How should the swabbing pattern be conducted on the Mueller-Hinton agar plate?

In a zigzag pattern across the plate in multiple directions Signup and view all the answers

What is the main purpose of using antimicrobial chemicals in the laboratory?

To reduce microbial growth Signup and view all the answers

Which statement correctly differentiates between antiseptics and disinfectants?

Disinfectants are applied to non-living surfaces, antiseptics to living tissue. Signup and view all the answers

What does the Bacteriostatic effect refer to?

Inhibiting the growth of microbes Signup and view all the answers

What is the Death Reduction Time (DRT)?

Time to kill 90% of a microbial population Signup and view all the answers

Which two organisms were mentioned as test subjects in the disinfectant activity?

Bacillus pumilis and Escherichia coli Signup and view all the answers

What basic procedure is performed to evaluate the effectiveness of a disinfectant?

Apply disinfectant and incubate at 37C. Signup and view all the answers

Which of the following is an expected property of antimicrobial chemicals?

To potentially damage DNA and disrupt cell walls Signup and view all the answers

During the disinfectant test, how long should the bacteria be in contact with the disinfectant for effective evaluation?

10 minutes Signup and view all the answers

Study Notes

Labs 19 and 20: Chemical Control of Growth

Lab 19 focuses on disinfectants and antiseptics
Lab 20 focuses on antibiotics
Video links are provided for both labs
- Disinfectants and Antiseptics: https://youtu.be/pLY2t4lskD8, https://youtu.be/qvaY7S1enCA
- Antibiotics: https://youtu.be/5GHnxYmzXio

Lab 19 - Antiseptics and Disinfectants

Purpose: reduce microbial growth using antimicrobial chemicals
Antiseptic: applied to living tissue
Disinfectant: applied to non-living surfaces
Bacteriostatic effect: inhibits microbial growth
Bactericidal effect: kills microbes
Death Reduction Time (DRT): time to kill 90% of test microbes
Use Dilution Test: bacteria dried onto metal rings, placed in disinfectant for 10 minutes; rings transferred to nutrient agar

Lab 19 - Activity 1 - Disinfectant

Two organisms: B. pumilis and E. coli
Disinfectant is diluted as needed.
Transfer 5mL of disinfectant to sterile test tubes labeled for respective bacteria
Divide nutrient agar plates into quarters, labeled as per protocol; 0, D-30s, D-4, D-25 for disinfectant
Inoculate one sector of each plate corresponding to bacteria
Transfer 0.5mL of bacteria to each tube
Inoculate corresponding plates at each time point.
Incubate at 37°C and evaluate/score growth

Lab 19 - Using Chemicals to Kill Microbes - Disinfectant Results

How long does it take disinfectant to kill bacteria?

Lab 19 - Using Chemicals to Kill Microbes - Antiseptic Results

Degerming arm with alcohol

Lab 20 - Antibiotic Sensitivity: Kirby Bauer Test

Antibiotic: a molecule produced by one organism that inhibits or kills another
Produced by bacteria and fungi; also synthetic
Targets biological structures, processes, including cell wall synthesis, DNA replication and protein synthesis
Kirby-Bauer Test: used to evaluate antimicrobials via diffusion
Mueller-Hinton Agar: specialized agar for antibiotic diffusion
Zone of Inhibition: area around disk where bacterial growth is inhibited.
Minimum Inhibitory Concentration (MIC): minimum effective concentration of antibiotic.

Lab Manual 16 - Antibiotic Sensitivity

Two organisms: Pseudomonas aeruginosa and Staphylococcus aureus.
Swab Mueller-Hinton agar plate in three directions in a zig zag pattern.
Let stand 5 minutes to allow organisms to fully adhere to the agar.
Place 5 different antibiotic disks gently onto the agar plate.
Determine the diameter of the Zone of Influence.

Lab Manual 16 - Antibiotic Sensitivity - Results

Measure diameter of "Zone of Influence"
Compare measured diameter to a reference table
Classify bacteria as Sensitive (S), Intermediate (I), or Resistant (R) to the antibiotic

Lab 20 - Antibiotics

Questions regarding antibiotic sensitivity for E. coli and S. epidermidis

Antibiotic Sensitivity Chart

Table with antibiotic sensitivity data; includes codes, drug names, doses, and zone of inhibition data for varying bacterial resistance sensitivities (including gram-negatives, gram-positives, etc)

"Interactive" Measurements

Images showing "Interactive" measurements of zone of inhibition with ruler for bacterial resistant and sensitive measurements.

Learning Objectives

Lab 19: Explain exposure time for chemical disinfectants, factors for bacterial resistance, purpose of degerming, evaluate disinfection effectiveness.
Lab 20: Explain antibiotic sensitivity and resistance, purpose of Kirby-Bauer, interpret Kirby-Bauer test, classify antibiotics effectiveness.

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Description

Explore the principles of chemical control of microbial growth through Labs 19 and 20. Lab 19 focuses on antiseptics and disinfectants, while Lab 20 delves into antibiotics. Videos provided will enhance your understanding of these critical topics in microbiology.