Controlling Bacterial Growth: Chemical and Physical Factors

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Questions and Answers

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?

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?

Physical and chemical

Antiseptic and disinfectant

Natural and synthetic (correct)

Bactericidal and bacteriostatic

What is the primary difference between antiseptics and disinfectants?

One is used on living things and the other on non-living things Signup and view all the answers

How does 75% alcohol affect bacteria?

It kills bacteria Signup and view all the answers

What is the primary mechanism of action of 75% alcohol on bacteria?

It acts as a hypotonic solution Signup and view all the answers

What is penicillin?

An antibiotic Signup and view all the answers

What is the primary difference between physical and chemical factors?

One is related to oxygen requirement and the other is not Signup and view all the answers

What is the effect of affecting permeability of the plasma membrane on the cell?

Nutrients will not enter the cell and waste will not leave Signup and view all the answers

What is the purpose of using Mueller-Hinton agar in the Kirby method?

To allow for the highest possible antibiotic diffusion rate Signup and view all the answers

What is the effect of a high titre of bacteria on the effectiveness of antibiotics in the Kirby method?

It decreases the effectiveness of antibiotics Signup and view all the answers

What type of antibiotics target a wide range of bacteria?

Broad-spectrum antibiotics Signup and view all the answers

What is the purpose of flaming the mouth of the nutrient broth tube in the Kirby method?

To sterilize the mouth of the tube Signup and view all the answers

What is the effect of breaking down the cell wall on the bacterial cell?

It can cause the cell to die Signup and view all the answers

What is the purpose of preparing a bacterial lawn in the Kirby method?

To ensure that each point on the media is inoculated with bacteria Signup and view all the answers

What is the effect of excess antibiotic on fungi in the Kirby method?

It can be used as a nutrient by fungi Signup and view all the answers

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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Description

Learn about the different methods to control bacterial growth, including chemical and physical factors, and how they can be classified as bactericidal or bacteriostatic.