Quiz 7

Question 1

How are bacteria counted under a microscope (e.g. do you just put them on any old slide)?

Answer 1

• a specialized slide called a Petroff-Hausser cell counter is used
• count the number of bacteria within a defined square, and multiply this number by 1,250,000 to get #cells/mL

Question 2

What are benefits of using microscopy to count bacteria? Drawbacks?

Answer 2

• can differentiate between individual cells and clumps of cells
• cannot distinguish b/t live vs dead cells

Question 3

How does one count relatively low bacteria levels within larger amounts of water?

Answer 3

• pass a large volume of water through filter paper to trap bacteria, touch filter to a Petri dish and allow it to grow, then count the colonies

Question 4

How does one use a spectrophotometer to measure growth? What is meant by turbidity? What are some limitations of using this method?

Answer 4

Bacteria is mixed in broth and allowed to culture for a while before being measured by a spectrophotometer. The more cloudy or “turbid” the broth becomes, the less light will be able to pass through the sample and the higher absorbance it will have
– it isn’t able to provide a direct cell count, only a relative quantitation because it’s measuring absorbance

Question 5

How can we use enzymes to measure bacterial growth?

Answer 5

can measure enzyme activity or metabolic pathway
- more activity = more cells

Question 6

What is meant by dry weight?

Answer 6

the dry weight of a sample is what’s left after centrifuging cells and discarding the liquid

Question 7

sterilization

Answer 7

complete removal of all microbes, including viruses and endospores

Question 8

disinfection

Answer 8

removal of most (99.9%) of microbes

Question 9

sanitization

Answer 9

essentially disinfection to defined health standards

Question 10

dry heat

Answer 10

involved heating to very high temps
- sterilizes
– incineration, baking

Question 11

boiling

Answer 11

destroys most pathogens, including nonendospores and most viruses

Question 12

pasteurization

Answer 12

involves the use of high heat for a short period of time
– milks, juices, some wine

Question 13

autoclaving

Answer 13

the use of pressurized steam in order to sterilize
- sterilizing medical equipment, canning

Question 14

Radiation – what are the two forms of radiation used? What are uses of each?

Answer 14

1) UV light damages DNA of microbes on surface, in air, and in water, but cannot penetrate thick specimens
2) ionizing radiation uses very high energy to damage DNA and membranes
– can penetrate products after packaging incl. medical equipment and meats

Question 15

Filtration – understand how filtration works. What are HEPA filters?

Answer 15

membrane filters are made with specific pore sizes so that anything bigger than the pores will not pass through
- filtering liquids in this way can achieve close to sterilization

HEPA filters remove larger microbes, and they’re used for filtering air in environments such as hospital isolation rooms and on airplanes