CH 6

A broth medium has been inoculated, and microbial numbers will be counted periodically to generate a bacterial growth curve. At 2 hours after inoculation, the culture has progressed through lag phase and is now in log phase. At this point, the population size is 1 million cells. The generation time is 30 minutes. Assuming the continuation of log growth, how many cells would there be at 2 hours of growth in log phase?

16 million

Put the following steps of bacterial replication in the correct order, starting from a parent cell. 1. Cell elongation 2. Septum formation 3. Chromosome replication 4. Separation of daughter cells

3, 1, 2, 4

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? A. 72 per milliliter B. 9 per milliliter C. 18 per milliliter D. 36 per milliliter

36 per milliliter

If you begin with six cells, how many cells would you have after three rounds of division?

48 cells

An experiment began with 4 cells and ended with 128 cells. How many generations did the cells go through?

5

A chemostat is continuous culture system that is designed to promote and prolong exponential growth and prevent bacteria from entering stationary phase. How might this work? A. Chemostats promote the formation of endospores, which enable the long-term survival of the bacteria. B. Chemostats provide a continued source of fresh nutrients and remove wastes and dead bacterial cells. C. Chemostats include detoxifying agents that inactivate growth-inhibiting toxins that develop during continued microbial growth. D. Chemostats include growth-promoting agents that prolong microbial growth.

Chemostats provide a continued source of fresh nutrients and remove wastes and dead bacterial cells.

Which of the following is NOT a step in bacterial cell division? A. Replication of the genetic material B. Splitting apart of two new daughter cells C. Disappearance of nuclear envelope D. Cell elongation

Disappearance of nuclear envelope

The Lake of the Ozarks is a human-made lake, so it collects runoff from coal strip-mining, fertilizers, resort wastewaters, and septic drainages. The average lake temperature is between 10∘C and 21∘C. Consider the physical requirements for growth and multiplication that would allow fecal coliforms to "blossom" in the Lake of the Ozarks. Which of the following would accurately describe these organisms? A. Facultative halophiles B. Extremophiles C. Psychrophiles D. Mesophiles

Facultative halophiles Psychrophiles Mesophiles

Most pathogenic bacteria are thermophiles. T/F

False

In addition to physical requirements, bacterial growth and multiplication also entails chemical requirements. Which of the following statements would accurately describe chemical requirements and conditions associated with growth in the Lake of the Ozarks environment? A. Fecal coliforms will likely contain enzymes to counteract toxic oxygen forms. B. The lake environment will support the growth of facultative anaerobes. C. Fecal coliforms will need to acquire trace elements for growth in the lake environment.

Fecal coliforms will likely contain enzymes to counteract toxic oxygen forms. The lake environment will support the growth of facultative anaerobes. Fecal coliforms will need to acquire trace elements for growth in the lake environment.

Which step of binary fission is the reason for genetically identical daughter cells? A. Replication of the bacterial chromosome B. Splitting of the two daughter cells C. Elongation of the cell D. There are four new daughter cells that result from one parental cell

Replication of the bacterial chromosome

When bacteria are inoculated into a new sterile nutrient broth, their numbers don't begin to increase immediately. Instead, there is a lag phase that may last for an hour or even several days. Why don't bacterial numbers increase immediately? A. The bacteria have to establish a biofilm before their numbers can increase. B. There are not enough nutrients for the bacteria to grow, and growth is delayed until there are some dead cells to cannibalize. C. The medium contains inhibitors that prohibit rapid growth of the bacteria, and these must be inactivated before bacterial numbers will increase. D. The bacteria must adjust to the nutrient content in the new medium, synthesizing necessary amino acids, growth factors, and enzymes.

The bacteria must adjust to the nutrient content in the new medium, synthesizing necessary amino acids, growth factors, and enzymes. A new medium may not have the same nutrients that were available in the medium from which an inoculum was taken. The bacteria may have to synthesize different amino acids, growth factors, or enzymes to enable them to grow in this new medium. Once those are synthesized, the growth rate is likely to increase, and the cells will move into log (exponential) growth phase.

After a period of rapid growth (log phase), bacterial growth rates will slow and enter the stationary phase. The number of viable cells no longer increases, but instead stays constant. In this activity you will indicate the statements that correctly describe what is happening during stationary phase. Reasons? A. The number of cells that are dying is balanced by the number of new cells that are being formed. B. Cells are not increasing in number because they have not yet adjusted to the nutrient availability in the new media. C. Harmful waste products may be accumulating. D. The cells are likely running out of nutrients.

The number of cells that are dying is balanced by the number of new cells that are being formed. Harmful waste products may be accumulating. The cells are likely running out of nutrients.

What would happen if the septum did not form during binary fission?

The parent cell would now have two copies of the chromosome.

Agar is used as a solidifying agent in microbiological media since few bacteria can degrade it. T/F

True

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

True

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

True

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

True

What results when a single bacterium reproduces? A. Two genetically unique daughter cells B. One parent cell and a genetically identical daughter cell C. Two genetically identical daughter cells D. One parent cell and a genetically different cell

Two genetically identical daughter cells

Bacteria naturally prefer company instead of solitude for growth. Examples of this kind of communal growth pattern can be found everywhere, from surfaces of the teeth and the intestines, to the surface of a slimy rock in the lake, to the thick floc that clogs water pipes. These examples of communal bacterial growth are known by what name? A. colony B. infectious unit C. biofilm D. planktonic unit

biofilm

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 A. infections can be transmitted from other people. B. their immune systems are weakened. C. biofilms develop on catheters. D. injected solutions are contaminated.

biofilms develop on catheters.

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?

determines the number of viable cells

The term aerotolerant anaerobe refers to an organism that

does not use oxygen but tolerates it.

Sampling lake water for microscopic organisms is not as easy as it sounds when you want to both count and identify species. In a given water sample, your bacteria of choice can be rare or difficult to culture, particularly given the mixture of bacteria in a biofilm. Which of the following culture media would be best for growing fecal coliforms when they are relatively less abundant than other bacteria in the lake? A. enrichment culture medium B. anaerobic culture medium C. complex culture medium D. basic culture medium

enrichment culture medium

Bacteria that can grow in the presence or absence of oxygen (O2) are called __________. A. facultative anaerobes B. obligate anaerobes C. microaerophiles D. obligate aerobes

facultative anaerobes

Cultures of the Lake of the Ozarks water samples were grown on enrichment media for identification. However, these organisms are present to some degree in all samples. An important question from a clinical perspective is whether or not there is a significant increase in the fecal coliform populations that would put people's health at risk. If you were part of the team investigating this outbreak, how would you best enumerate the fecal coliform threat? A. plate count culture B. filtration count culture C. serial dilution count culture D. direct microscopic counts

filtration count culture

Salts and sugars work to preserve foods by creating a

hypertonic environment.

Which of the following is NOT a direct method to measure microbial growth? A. metabolic activity B. direct microscopic count C. standard plate count D. filtration on a support membrane followed by incubation on medium E. most probable number (MPN)

metabolic activity

This activity asks you to consider various methods of counting or estimating the size of bacterial populations and to select the method that will provide the most accurate data for plotting a bacterial growth curve. Which of the following methods would be most appropriate for gathering data to plot a bacterial growth curve throughout the four phases? A. direct microscopic count B. plate count C. indirect estimate based on turbidity D. electronic cell counter

plate count

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

requires no incubation time