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Chemical disinfectant, zone of inhibition, bacteria vs virus

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Not all chemical disinfectants are bactericidal. Depending on the different mechanisms disinfectants use, they can be categorized mainly as bactericidal or bacteriostatic. This solution discusses briefly the mechanisms, similarities and differences between bactericidal and bacteriostatic disinfectants.

This response also discusses the mechanisms behind the "zone of inhibition" using the Kirby-Bauer method and what factors influence this phenomenon.

Lastly, why antibacterials are not used to destroy viruses is examined, and by extension, the differences between bacteria and viruses leading to this fact are examined.

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Disinfectants are, for the most part, bactericidal. However, many chemical disinfectants require the compound to be at a particular concentration before it can properly kill off bacteria. With certain disinfectants that disrupt cellular metabolism, including the making and usage of DNA, at lower than lethal concentrations, the compound is likely to restrict growth of the bacteria instead of killing it. This is deemed bacteriostatic - the population of bacteria fails to grow - and the effects of which can likely be completely reversed once the compound is removed.

The KB method relies on:
1) Diffusion of the antibiotic through the agar gel and subsequent concentration at a given point away from the source of the antibiotic
2) Sensitivity of bacteria to the ...

Solution Summary

This solution discusses briefly the mechanisms, similarities and differences between bactericidal and bacteriostatic disinfectants.

See Also This Related BrainMass Solution

Microbiology Review

1. What does bactericidal mean? Bacteriostatic? Virucidal? Fungistatic?
2. Why are control cultures necessary in evaluating disinfectants?
3. What factors can influence the activity of a disinfectant?
4. Why do microorganisms differ in their response to disinfectants?
5. What microorganisms are most susceptible to disinfectants?
6. What is meant by antimicrobial resistance? Susceptibility?
7. Why are pure cultures used for antimicrobial susceptibility testing?
8. Would it be acceptable to use a mixed culture for this test? Why?
9. List three factors that can influence the accuracy of the test.
10. When performing a broth dilution test, why is it necessary to include a growth control tube?
A sterility control tube?

Please see the attachments for the rest of the questions.

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