Q: If the decimal reduction time ($$D) $$for a bacterial population at 70°C is 2 minutes, how long will it take to reduce a population of $$10^6$$ cells to $$10^3$$ cells?

$$6$$ minutes$$,\text{since}\ D = 2\ \text{min},\ 10^6$ \rightarrow 10^3$\ \text{is}\ 3\ \text{log reductions},\ 3 \times 2 = 6\ \text{min}$$

Question 1

Which of the following best describes the process of binary fission in prokaryotes?

Accepted Answer

A process where a single cell divides into two genetically identical daughter cells after chromosome replication and septum formation.

Question 2

During which phase of bacterial growth in a closed batch system is the generation time most accurately measured, and why?

Accepted Answer

Log (exponential) phase, because cells are dividing rapidly and population increases exponentially.

Question 3

A bacterial culture is exposed to a temperature of 80°C. Which group of microbes is most likely to survive and thrive under these conditions?

Accepted Answer

Extreme thermophiles

Question 4

A microbe is isolated from a hot spring with a pH of 2. Which classification best describes this organism?

Accepted Answer

Acidophile

Question 5

Which mechanism allows acidophiles to survive in environments with low pH?

Accepted Answer

Using proton pumps to export excess H$$^+$$ ions and specialized membrane structures to limit proton entry.

Question 6

Which of the following statements about halophiles is correct?

Accepted Answer

Halophiles thrive in high-salt environments (≥9%) and survive osmotic stress by maintaining high concentrations of organic materials and ions in their cytoplasm.

Question 7

A clinical sample is suspected to contain obligate anaerobes. Which of the following is most important when collecting and transporting this sample?

Accepted Answer

Maintaining anaerobic conditions during collection and transport to prevent exposure to oxygen.

Question 8

Which type of media would you use to distinguish between two bacterial species based on their ability to ferment lactose, and why?

Accepted Answer

Differential media, because it allows visible distinction (such as color change) between species based on lactose fermentation.

Question 9

Which of the following best describes the difference between sterilization and disinfection?

Accepted Answer

Sterilization eliminates all bacteria, viruses, and endospores; disinfection reduces microbial numbers but does not eliminate all microbes.

Question 10

A bacteriostatic agent is applied to a bacterial culture. What is the expected outcome?

Accepted Answer

The agent inhibits bacterial growth, but does not necessarily kill the bacteria.

Question 11

Which heat treatment is most effective for sterilizing surgical tools and laboratory equipment, and why?

Accepted Answer

Autoclaving, because it uses steam heat under pressure at 121°C and 15 psi to sterilize and is effective against endospores.

Question 12

If the decimal reduction time ($$D) $$for a bacterial population at 70°C is 2 minutes, how long will it take to reduce a population of $$10^6$$ cells to $$10^3$$ cells?

Accepted Answer

$$6$$ minutes$$,	ext{since}\ D = 2\ 	ext{min},\ 10^6$ ightarrow 10^3$\ 	ext{is}\ 3\ 	ext{log reductions},\ 3 	imes 2 = 6\ 	ext{min}$$

Question 13

Which physical method is most appropriate for sterilizing heat-sensitive solutions, such as certain vaccines?

Accepted Answer

Membrane filtration

Question 14

A hospital uses HEPA filters in its ventilation system. What is the primary purpose of these filters?

Accepted Answer

To remove 99.97% of airborne particles 0.3 micrometers or larger, reducing microbial load in the air.

Question 15

Which class of germicide would be most appropriate for disinfecting skin prior to an injection, and why?

Accepted Answer

An antiseptic, because it is applied to living tissue to limit microbial growth.

Question 16

Which factor is LEAST important when selecting a germicide for disinfecting a hospital surface?

Accepted Answer

The color of the germicide

Question 17

A laboratory technician needs to sterilize a plastic Petri dish that cannot withstand high temperatures or moisture. Which germicide is most suitable?

Accepted Answer

Ethylene oxide gas, because it sterilizes temperature-sensitive and moisture-sensitive materials.

Question 18

A patient sample is collected for suspected infection with a fastidious organism. Which type of media should be used to ensure growth?

Accepted Answer

Complex media, because it contains a mixture of ingredients and supports the growth of fastidious organisms.

Question 19

Which of the following best describes the action of halogens as germicides?

Accepted Answer

They act as oxidizing agents that damage proteins and nucleic acids.

Fundamentals of Microbial Growth: Study Notes

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