chapter 6

Thirty- six colonies grew in nutrient agar from 1.0 ml of undiluted sample in a standard plate count. How many cells were in the original sample? 72 per milliliter 18 per milliliter 4 per milliliter 36 per milliliter 9 per milliliter

36 per milliliter

Most fungi grow best at pH 5. 9. 7. 14. 1.

5

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

Most bacteria grow best at pH 1. 5. 14. 9. 7.

7

Three cells with generation times of 60 minutes are inoculated into a culture medium. How many cells are there after 5 hours? 96 32 15 900 180

96

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

A

In table 6.1, in which medium (or media) would an autotroph grow?

A

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 sections of the graph illustrate a logarithmic change in cell numbers?

B and D

The biosafety level (BSL) for most introductory microbiology laboratories is BSL-1. BSL-2. BSL-3. BSL-4.

BSL-1.

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

BSL-3

in figure 6.1 which line shows the growth of an OBLIGATE aerobe incubated anaerobically

C

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

Bacterial generation times for four different bacterial species were calculated in the media listed in Table 6.3. All media were prepared with pure distilled water and incubated aerobically in the light. Compare and contrast the growth requirements of the four bacteria listed above. Which of the media, if any, are chemically defined?

Nitrobacter will only grow in the NaCL, NO3-, and MgSO4 medium ; whereas Lactobacillus requires the medium with 19 amino acids to grow. Since all the chemical components are known, all of the medias presented are chemically defined

A patient with a heart pacemaker recieved antibiotic therapy for streptococcal bactermia. One month later, he was treated for recurrence of the bactermia. When he returned six weeks later, again with bactermia, the physician recommended replacing the pacemaker. Why did this cure his condition?

Replacing the pacemaker he had previously with a new one would cure his condition since the previous pacemaker contains a biofilm caused by a bacteria. A new pacemaker without biofilm on it should result in the bactermia being cured.

Turbidity is an indirect measurement of bacterial growth that can be measured using a spectrophotometer.

True

In Figure 6.1, which line best illustrates the growth of a FACULTATIVE ANAEROBE incubated aerobically?

a

In one hospital, Pseudomonas aeruginosa serotype 10 infected the biliary 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

Figure 6.1, which line best depicts a facultative anaerobe in the ABSENCE of O2? a b c

b

In Figure 6.1, which line best depicts a psychrotroph incubated at 0°C? a b c

b

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

b

Most bacteria reproduce by

binary fission

Patients with indwelling catheters are susceptible to infections because

biofilms develop on catheters

The addition of which of the following to a culture medium will neutralize acids? carbon heat buffers pH sugars

buffers

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? a b c d a and c

c

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

c

Pathogenic bacteria isolated from the respiratory or intestinal tracts of humans are strict aerobes that grow best in candle jars. capnophiles that prefer highly oxygenated growth conditions. capnophiles that grow best in carbon dioxide incubators. facultative anaerobes that require reducing media for growth. strict aerobes that grow best in reducing media.

capnophiles that grow best in carbon dioxide incubators.

Which enzyme catalyzes the reaction: 2H2O2 → 2H2O + O2? catalase oxidase peroxidase superoxide dismutase

catalase

which enzyme catalyzes the reaction: O2- + O2- + 2H+ --> H2O2 + O2?

catalase

a culture medium consisting of agar, peptone, and beef heart is a

complex medium

Which of the following is an advantage of the standard plate count? can be used to count heat-sensitive bacteria can be performed on very dilute samples, such as lake water determines the number of viable cells provides immediate results can readily count cells that form aggregates

determines the number of viable cells

The term aerotolerant anaerobe refers to an organism that requires less oxygen than is present in air. tolerates normal atmospheric nitrogen gas levels. requires more oxygen than is present in air. is killed by oxygen. does not use oxygen but tolerates it.

does not use oxygen but tolerates it.

In Figure 6.3, which tube shows the expected growth pattern for a microaerophile? a b c d e

e

The data in Table 6.2 indicate that S. aureus is a(n) facultative anaerobe. aerobe. mesophile. facultative halophile. halophile.

facultative halophile

which group of microorganisms is most likely to spoil a freshwater trout preserved with salt?

facultative halophiles

In performing a ten- fold dilutions series from a sample containing 10,000 bacteria per milliliter, the fourth tube in the dilution series will have 10 cells per milliliter. True False

false

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

false

most pathogenic bacteria are thermophiles

false

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

glucose consumption

During which growth phase will gram- positive bacteria be most susceptible to penicillin? lag phase death phase log phase stationary phase The culture is equally susceptible during all phases.

log phase

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

metabolic activity

the source of nutrients in nutrient agar is peptone and NaCl. agar and NaCl. gelatin. peptone and beef extract. agar.

peptone and beef extract

Which enzyme catalyzes the reaction H2O2 + 2H --> 2H2O

peroxidase

Which of the following elements is NOT correctly matched with its cellular function? magnesium and potassium — required as cofactors for enzymes phosphorus — used for production of carbohydrates. phosphorus — incorporated into nucleic acids nitrogen — needed for amino acid synthesis sulfur — used for synthesis of thiamin and biotin

phosphorus — used for production of carbohydrates.

Which of the following is an advantage of the direct microscopic count? requires a large number of cells can readily count organisms that are motile requires no incubation time sample volume is unknown can easily distinguish live from dead cells

requires no incubation time

consider a culture medium on which only gram- positive organisms such as Staphylococcus aureus colonies can grow due to an elevated NaCl level. A yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the pH as a result and changing the color of a pH indicator chemical. This type of medium would be referred to as an

selective and differential medium

Which of the following is the best definition of generation time? the minimum rate of doubling the length of time needed for a cell to divide the duration of log phase the length of time needed for lag phase the time needed for nuclear division

the length of time needed for a cell to divide

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 4 hours, you can reasonably expect to have

the same number of cells in both

which of the following pairs of microbe classification terms and optimal growth temperatures is mismatched?

thermophile- growth at 37 degrees Celsius

An isolated colony on a streak plate contains millions (or even billions) of identical cells all arising from one initial cell. True False

true

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

true

Laboratory cultivation of obligate anaerobes requires reducing media or special growth chambers filled with inert gases. True False

true

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

true

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

true

Which of the following is an organic growth factor?

vitamin B1