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Exam 6: Microbial Growth

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Question 21

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Pathogenic bacteria isolated from the respiratory or intestinal tracts of humans are

A) strict aerobes that grow best in candle jars.
B) capnophiles that grow best in carbon dioxide incubators.
C) facultative anaerobes that require reducing media for growth.
D) strict aerobes that grow best in reducing media.
E) capnophiles that prefer highly oxygenated growth conditions.

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Question 22

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Figure 6.1 -In Figure 6.1,which line best illustrates the growth of a facultative anaerobe incubated aerobically?

A) a
B) b
C) c

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Question 23

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Nitrogen-fixing bacteria,such as cyanobacteria,can use atmospheric nitrogen (N₂)for their nitrogen source.

The U.S.Food and Drug Administration convention when performing pour or spread plate counts is to count only plates with ________ colonies.

As part of an experiment where absorbance values are measured using a spectrophotometer,you are taking readings of your sample every 20 minutes.The non-motile microbe you're testing has a generation time of roughly 20 minutes at an incubation temperature right around room temperature.Things start out fine,with the expected results - as time goes by at the correct incubation temperature,absorbance starts to rise as the medium starts to become more cloudy with growing microorganisms.But roughly 2 hours into the process,you notice that the absorbance levels flatten out,and then start to decrease unexpectedly.What is most likely taking place in your experiment?

In measuring turbidity of a culture in indirect measurement of bacterial growth,absorbance and transmittance are identical and interchangeable values.

Figure 6.1 -In Figure 6.1,which line shows the growth of an obligate aerobe incubated anaerobically?

Salts and sugars work to preserve foods by creating a

Figure 6.3 -In Figure 6.3,which tube shows the expected growth pattern for a microaerophile?

Which of the following is NOT a direct method to measure microbial growth?

Which of the following is an organic growth factor?

Figure 6.2 -Figure 6.2 shows a typical bacterial growth curve with the y-axis indicating the log of the number of bacteria and the x-axis indicating time in culture.In the figure,which section (or sections) shows a growth phase where the number of cells dying equals the number of cells dividing?

In one hospital,Pseudomonas aeruginosa serotype 10 infected the biliary tract of 10 percent of 1300 patients who underwent gastrointestinal endoscopic procedures.After each use,endoscopes were washed with an automatic reprocessor that flushed detergent and glutaraldehyde through the endoscopes,followed by a tap water rinse.P.aeruginosa serotype 10 was not isolated from the detergent,glutaraldehyde,or tap water.What was the source of the infections?

Which of the following is an advantage of the standard plate count?

Figure 6.1 -In Figure 6.1,which line best depicts an obligate anaerobe in the presence of O₂?

Filtration methods,followed by growth of the bacteria trapped on the filters in growth media,are used to count bacteria present in very low concentrations,such as in lakes and streams.

Which of the following is the best definition of generation time?

The addition of which of the following to a culture medium will neutralize acids?

Three cells with generation times of 60 minutes are inoculated into a culture medium.Assuming no lag phase takes place,how many cells are there after 5 hours?

A sample of ocean water is tested for its bacterial content in a plate count assay.A one-milliliter sample of the water is diluted in a 1:10 dilution series.0.1 milliliter of the second dilution tube is plated in a pour plate.After incubation,the plate has 191 colonies,indicating that the original water sample contained