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Questions and Answers
What is the primary difference between bactericidal and bacteriostatic factors?
What is the primary difference between bactericidal and bacteriostatic factors?
- One is used on living things and the other on non-living things
- One kills bacteria and the other slows down growth (correct)
- One is physical and the other is chemical
- One is natural and the other is synthetic
What is the effect of high temperature on bacterial growth?
What is the effect of high temperature on bacterial growth?
- It causes bacterial growth to stop temporarily
- It has no effect on bacterial growth
- It kills bacteria (correct)
- It slows down bacterial growth
What is the classification of chemical factors based on their source?
What is the classification of chemical factors based on their source?
- Physical and chemical
- Antiseptic and disinfectant
- Natural and synthetic (correct)
- Bactericidal and bacteriostatic
What is the primary difference between antiseptics and disinfectants?
What is the primary difference between antiseptics and disinfectants?
How does 75% alcohol affect bacteria?
How does 75% alcohol affect bacteria?
What is the primary mechanism of action of 75% alcohol on bacteria?
What is the primary mechanism of action of 75% alcohol on bacteria?
What is penicillin?
What is penicillin?
What is the primary difference between physical and chemical factors?
What is the primary difference between physical and chemical factors?
What is the effect of affecting permeability of the plasma membrane on the cell?
What is the effect of affecting permeability of the plasma membrane on the cell?
What is the purpose of using Mueller-Hinton agar in the Kirby method?
What is the purpose of using Mueller-Hinton agar in the Kirby method?
What is the effect of a high titre of bacteria on the effectiveness of antibiotics in the Kirby method?
What is the effect of a high titre of bacteria on the effectiveness of antibiotics in the Kirby method?
What type of antibiotics target a wide range of bacteria?
What type of antibiotics target a wide range of bacteria?
What is the purpose of flaming the mouth of the nutrient broth tube in the Kirby method?
What is the purpose of flaming the mouth of the nutrient broth tube in the Kirby method?
What is the effect of breaking down the cell wall on the bacterial cell?
What is the effect of breaking down the cell wall on the bacterial cell?
What is the purpose of preparing a bacterial lawn in the Kirby method?
What is the purpose of preparing a bacterial lawn in the Kirby method?
What is the effect of excess antibiotic on fungi in the Kirby method?
What is the effect of excess antibiotic on fungi in the Kirby method?
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Study Notes
Controlling Bacterial Growth
- Chemical and physical factors can control bacterial growth.
Classification of Chemical and Physical Factors
- Bactericidal factors: kill bacteria, preventing regrowth even in optimum conditions.
- Bacteriostatic factors: slow down bacterial growth, allowing regrowth in optimum conditions.
Physical Factors
- Low temperature: bacteriostatic, stopping growth until temperatures rise.
- High temperature: bactericidal, denaturing bacterial enzymes and killing bacteria.
Classification of Chemical Factors
- Based on source: natural (e.g., penicillin derived from Penicillium fungi) or synthetic (e.g., artificially produced penicillin).
- Based on application: antiseptic (used on human body, e.g., antibiotics) or disinfectant (used on surfaces, e.g., alcohol, HiGeen, Lifebuoy soap).
Chemical Factors
- 75% alcohol: a bactericide composed of 75 mL alcohol and 25 mL water, killing bacteria in two ways:
- Dissolving bacterial cell wall, leaving a protoplast.
- Causing protoplast to lyse/burst through hypotonic solution.
Effects of Bacteriostatic and Bactericidal Factors on Bacterial Growth
- Cell wall: break down or prevent synthesis.
- Plasma membrane: break down, prevent synthesis, or affect permeability.
- Genetic material: interfere with DNA replication, leading to no cell growth.
- Transcription and translation: prevent transcription or translation.
- Metabolic pathways: inhibit enzymatic function.
Studying the Effects of Antibiotics on Bacteria
- Using the Kirby method (disc diffusion method).
- Factors affecting the Kirby method:
- Type of media: must have high antibiotic diffusion rate and not react with antibiotic (e.g., Mueller-Hinton agar).
- Titre of bacteria: must not exceed 10^7.
- Type of antibiotic: broad-spectrum or narrow-spectrum.
- Concentration of antibiotic: optimal concentrations vary.
- Type of bacteria: affects Kirby method results.
Kirby Method (Disc Diffusion Method) Procedure
- Prepare a bacterial lawn on the media.
- Add antibiotic discs.
- Incubate and measure the zone of inhibition.
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