Ch. 7 - The Control of Microbial Growth

Tortora - Microbiology: An Introduction 14th Edition

Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook

Tortora 14th Edition

Ch. 7 - The Control of Microbial Growth

Problem 4

Chapter 7, Problem 4

The antimicrobial effect of gamma radiation is due to:(a) .
The antimicrobial effect of ultraviolet radiation is due to: (b) .

Verified step by step guidance

Step 1: Understand that gamma radiation and ultraviolet (UV) radiation have different mechanisms by which they exert antimicrobial effects.

Step 2: Recall that gamma radiation is a form of ionizing radiation, which means it has enough energy to remove tightly bound electrons from atoms, creating ions. This ionization leads to damage in microbial DNA and other cellular components.

Step 3: Therefore, the antimicrobial effect of gamma radiation is primarily due to the ionization and generation of free radicals that cause breaks in DNA strands and damage to cellular molecules.

Step 4: On the other hand, ultraviolet radiation is non-ionizing and does not cause ionization but instead causes specific damage to DNA by inducing the formation of thymine dimers, which are covalent linkages between adjacent thymine bases in DNA.

Step 5: These thymine dimers distort the DNA structure, interfering with replication and transcription, ultimately leading to microbial death or inability to reproduce.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mechanism of Gamma Radiation on Microorganisms

Gamma radiation kills microbes primarily by causing ionization that leads to the formation of free radicals. These free radicals damage critical cellular components such as DNA, proteins, and membranes, resulting in cell death or loss of reproductive ability.

Mechanism of Ultraviolet (UV) Radiation on Microorganisms

Ultraviolet radiation exerts its antimicrobial effect mainly by inducing DNA damage, specifically forming thymine dimers. These dimers disrupt DNA replication and transcription, preventing microbial growth and leading to cell death.

Differences Between Ionizing and Non-Ionizing Radiation

Gamma radiation is ionizing, meaning it has enough energy to remove tightly bound electrons, causing direct and indirect damage to cellular molecules. UV radiation is non-ionizing and primarily causes damage through chemical changes like DNA dimer formation rather than ionization.

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Textbook Question

Thermal death point is not considered an accurate measure of the effectiveness of heat sterilization. List three factors that can alter thermal death point.

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Textbook Question

Which of the following is used to control microbial growth in foods?

a. Organic acids

b. Alcohols

c. Aldehydes

d. Heavy metals

e. All of the above

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Textbook Question

A bacterial culture was in log phase in the following figure. At time x, an antibacterial compound was added to the culture. Draw the lines indicating the addition of a bactericidal compound and a bacteriostatic compound. Explain why the viable count does not immediately drop to zero at x.

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Textbook Question

Use the following information to answer questions 6 and 7. The data were obtained from a use-dilution test comparing four disinfectants against Salmonella Choleraesuis.

G = growth, NG = no growth

Which disinfectant is the most effective?

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Textbook Question

Which of these disinfectants does not act by disrupting the plasma membrane?

a. Phenolics

b. Phenol

c. Quats

d. Halogens

e. Biguanides

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