MCB 2000 Chapter Notes - Chapter 11: Desiccation, Membrane Technology, Neisseria

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The purpose of controlling microbial growth to stop spreading the diseases or food spoilage. Terminology: bactericidal (germicidal, microbicidal)- agent that destroys or kills bacteria (suffix cide - kill, bacteriostatic - agent that inhibits bacterial growth (stasis - to stop) What is microbial death: permanent loss of reproductive capabilities, the cell structures become dysfunctional, antimicrobial treatment leads to killing of microbial population at the constant rate. Factors that affect death rate: time of exposure (lower temp. can be compensated with longer exposure, the number of microbes, microbial characteristics (endospore, vegetative cells, agent used, environmental influences (suspending medium, ph) The mode of action of antimicrobial agents: plasma membrane - when damaged, cell content leaks into the surrounding medium, proteins- enzyme active sites inactivated. Blocking the active sites: nucleic acid - radiation or some chemicals lethally damage the dna or rna (microbes can no longer replicate) Uv radiation causes formation of dimmers between two thymine bases.

Related Questions

For each series of questions, read carefully to be sure you are addressing the right

content of the question. As always, if the question applies to more than one, indicate which ones.

Please use the terms provided!

A. We talked about the physical methods of antimicrobial treatment, which include

Pasteurization, filtration, and irradiation. Briefly answer the following questions. If the question

applies to more than one, indicate which ones. Use these terms.

a. Which might be used to disinfect a counter top?

b. Which removes, rather than kills, microbes?

c. Which can be used to reduce the number of microbes in food?

d. Which of the above methods is most appropriate for sterilizing the packages of empty Petri

dishes like we used in the cutting-board lab (into which we poured agar and then incubated)?

B. Ethylene oxide is a gas, hydrogen peroxide is an antiseptic, and gamma-irradiation is a form of

ionizing radiation. Compare and contrast these treatments.

a. Which of the above could you or I apply at home or in the Hartnell microbiology laboratory?

b. Which of the above is used to treat wounds?

c. Which of the above could be used to treat substances that cannot get wet?

d. Which of the above can damage DNA?

C. Compare and contrast refrigeration, pickling (packing in brine, or salt water), and benzoic acid

(a preservative) and their effects on food. Continued on the next page.

a. Which of the above is not used to control growth of microbes in bread?

b. Which controls microbial growth in food by lowering the pH?

c. Which controls microbial growth in food by drawing water out of cells (the purpose of the

technique)?

MCB 2000 Chapter Notes - Chapter 11: Desiccation, Membrane Technology, Neisseria

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