Most bacteria grow best at pH

pH 7

A sample of well 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. One milliliter of the fourth dilution tube is plated in a pour plate. After incubation, the plate has 83 colonies, indicating that the original water sample contained

830,000 cells per milliliter.

Which of the following is an advantage of the direct microscopic count?

requires no incubation time

The ________ method is used to indirectly measure microbial growth of filamentous bacteria and molds.

dry weight

Assume you inoculated 100 cells, with a generation time of 20 minutes, into 100 ml of nutrient broth. You then inoculated 100 cells of the same species into 200 ml of nutrient broth. After incubation for 3 hours, you can reasonably expect to have

the same number of cells in both.

For the three types of media in Table 6.1, which medium (or media) is/are chemically defined?

A

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

determines the number of viable cells

The source of nutrients in nutrient agar is

peptone and beef extract.

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?

96

Which of the following is an example of a metabolic activity that could be used to measure microbial growth?

glucose consumption

When cultivating anaerobic organisms in the laboratory setting, a candle jar is sufficient for the vast majority of organisms.

False

Figure 6.1, which line best depicts a facultative anaerobe in the absence of O2?

b

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?

c

Most fungi grow best at pH

5

Which enzyme catalyzes the reaction: O2- + O2- + 2H+ → H2O2 + O2?

superoxide dismutase

The biosafety level (BSL) for a clinical microbiology laboratory working with potentially airborne pathogens, such as tuberculosis bacteria, is

BSL-3.

Pure cultures can easily be obtained on streak plates, even if the desired bacteria are present in very low concentrations in the initial culture broth.

True

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

a

Which of the following is an organic growth factor?

vitamin B1

Thirty-six colonies grew in nutrient agar from 1.0 ml of undiluted sample in a standard plate count. How many viable and culturable cells were in the original sample?

36 per milliliter

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

191,000 cells per milliliter.

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

false

Which of the following elements is NOT correctly matched with its cellular function?

phosphorus – used for production of carbohydrates.

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

c

A sample of milk is tested for its bacterial content in a plate count assay. A one-milliliter sample of the milk is diluted in a 1:10 dilution series. One milliliter of the third dilution tube is plated in a pour plate. After incubation, the plate has 54 colonies, indicating that the original milk sample contained

54,000 cells per milliliter.

In Figure 6.3, which tube shows the expected growth pattern for a facultative anaerobe?

b

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

metabolic activity

Patients with indwelling catheters (long-term tubes inserted into body orifices for drainage, such as through the urethra and into the urinary bladder) are susceptible to infections because

biofilms develop on catheters.

Most pathogenic bacteria are thermophiles.

false

Bacterial growth refers to an increase in the numbers of cells in a bacterial culture.

true

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?

a biofilm in the reprocessor

If cells are grown in media containing amino acids labeled with radioactive nitrogen (15N), most of the radioactivity will be found in the cells'

DNA and proteins.

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

25 to 250

The term aerotolerant anaerobe refers to an organism that

does not use oxygen but tolerates it.

Salts and sugars work to preserve foods by creating a

hypertonic environment.

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

buffers

Which enzyme catalyzes the following reaction? 2H2O2 → 2H2O + O2

catalase

During which growth phase will gram-positive bacteria be most susceptible to penicillin?

log phase