Ch. 7 - The Control of Microbial Growth

Tortora - Microbiology: An Introduction 14th Edition

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Tortora 14th Edition

Ch. 7 - The Control of Microbial Growth

Problem 8

Chapter 7, Problem 8

The use-dilution values for two disinfectants tested under the same conditions are as follows:
Disinfectant A—1:2
Disinfectant B—1:10,000.
If both disinfectants are designed for the same purpose, which would you select?

Verified step by step guidance

Understand the meaning of use-dilution values: A use-dilution value indicates the dilution factor at which a disinfectant is still effective. For example, a use-dilution of 1:2 means the disinfectant is effective when diluted to half its original concentration, while 1:10,000 means it is effective even when diluted 10,000 times.

Compare the two disinfectants based on their use-dilution values: Disinfectant A has a use-dilution of 1:2, meaning it requires a relatively high concentration to be effective. Disinfectant B has a use-dilution of 1:10,000, meaning it remains effective even at a very low concentration.

Interpret the practical implications: A higher dilution factor (like 1:10,000) suggests that less disinfectant is needed to achieve the same antimicrobial effect, which can be more cost-effective and potentially less toxic or corrosive.

Consider other factors that might influence the choice, such as the spectrum of activity, safety, environmental impact, and compatibility with surfaces, but based solely on use-dilution values, the disinfectant effective at higher dilution is generally preferred.

Conclude that, based on the use-dilution values alone, Disinfectant B (1:10,000) would be the better choice because it is effective at a much greater dilution, indicating higher potency or efficiency.

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Key Concepts

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

Use-Dilution Test

The use-dilution test measures the effectiveness of a disinfectant by determining the highest dilution that still kills a standard number of microbes. A lower dilution ratio means the disinfectant is effective at a stronger concentration, while a higher dilution ratio indicates effectiveness even when highly diluted.

Disinfectant Potency and Concentration

Disinfectant potency refers to how strong or effective a disinfectant is at killing microbes. A disinfectant effective at a higher dilution (e.g., 1:10,000) is more potent because it requires less concentrated solution to achieve microbial kill compared to one effective only at a lower dilution (e.g., 1:2).

Selection Criteria for Disinfectants

Choosing a disinfectant depends on factors like potency, safety, cost, and intended use. When two disinfectants serve the same purpose, the one effective at a higher dilution is generally preferred due to better efficiency and potential cost savings.

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Related Practice

Textbook Question

How do salts and sugars preserve foods? Why are these considered physical rather than chemical methods of microbial control? Name one food that is preserved with sugar and one preserved with salt. How do you account for the occasional growth of Penicillium mold in jelly, which is 50% sucrose?

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Textbook Question

You and your classmates are trying to determine how a disinfectant might kill cells. You observe that when you spill the disinfectant in a tube of reduced litmus milk, the litmus turns blue again. You suggest to your classmates that:

a. The disinfectant might inhibit cell wall synthesis

b. The disinfectant might oxidize molecules

c. The disinfectant might inhibit protein synthesis

d. The disinfectant might denature proteins

e. The disinfectant might damage DNA

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Textbook Question

A large hospital washes burn patients in a stainless steel tub. After each patient, the tub is cleaned with a quat. It was noticed that 14 of 20 burn patients acquired Pseudomonas infections after being bathed. Provide an explanation for this high rate of infection.

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Textbook Question

Which of the following is not a characteristic of quaternary ammonium compounds?

a. Bactericidal against gram-positive bacteria

b. Sporicidal

c. Amebicidal

d. Fungicidal

e. Kills enveloped viruses

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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(s) is (are) bactericidal?

a. A,B,C, and D

b. A,C, and D

c. A only

d. B only

e. None of the above

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Textbook Question

Which of the following is most likely to be bactericidal?

a. Membrane filtration