Microbial Growth

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In microbiology lab, you make three different culture plates: one general purpose plate, one selective media plate, and one differential media plate. Unfortunately, you forget to label the different plates, so you do not know which is which. To determine the identity of each plate, you inoculate it with two different strains of laboratory bacteria. Which of the following results would indicate the plate you used was the general purpose media?

Both organisms would grow equally well.
In microbiology lab, you make three different culture plates: one general purpose plate, one selective media plate, and one differential media plate. Unfortunately, you forget to label the different plates, so you do not know which is which. To determine the identity of each plate, you inoculate it with two different strains of laboratory bacteria. After inoculation, you see that a particular plate has allowed both organisms to grow, but one has changed color. Which plate do you think this is?
enrichment media
Which of the following would you expect to be a function of MacConkey agar? Mark all that apply.

change the color of some organisms based on their metabolic characteristics inhibit the growth of certain bacteria

What enables the copied chromosomes to separate during binary fission?
The chromosomes are attached to different parts of cell membrane, which elongates and thus separates the chromosomes.
How long does it take for the daughter cells from one round of replication to replicate themselves?
No time is required -- they are ready to divide immediately after DNA replication and separation of the daughter cells is complete if conditions are right.
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
What would happen if the septum did not form during binary fission?
The parent cell would now have two copies of the chromosome.
Starting with three cells, how many cells would result from three rounds of replication?
What results when a single bacterium reproduces?
Two genetically identical daughter cells
If you begin with six cells, how many cells would you have after three rounds of division?
Forty-eight cells
Which of the following is NOT a step in bacterial cell division?
Disappearance of nuclear envelope
Which step of binary fission is the reason for genetically identical daughter cells?
Replication of the bacterial chromosome
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? Check all that apply.
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? Select all of the following statements that are true regarding fecal coliforms in the Lake of the Ozarks.
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?
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?
enrichment culture medium
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?
filtration count culture
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?
The bacteria must adjust to the nutrient content in the new medium, synthesizing necessary amino acids, growth factors, and enzymes.
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. Select each statement that accurately describes what is happening to bacterial cultures during stationary phase.
Harmful waste products may be accumulating.

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?
Chemostats provide a continued source of fresh nutrients and remove wastes and dead bacterial cells.
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 4 hours after inoculation?
16 million
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?
plate count
If cells are grown in media containing amino acids labeled with radioactive nitrogen (15N), most of radioactivity will be found in the cells
DNA and proteins.
Most bacteria reproduce by
binary fission.
Which of the following shows the moist heat methods in order of the temperature used (highest to lowest)?
Ultrahigh>Autoclave>Boiling>Batch Pasteurization
_______________ is a process used to destroy pathogens in food and drinks. It must be done at a lower temperature than other methods so that _______________.
Pasteurization; the taste of the food or drink will not be altered
During a flood, a community's well water system is contaminated with a pathogenic fungus. If the residents boil their water for 15 minutes prior to consumption, will they be protected?
yes, most likely
Which of the following is an example of microbial control? Select all that apply.
Sue washes off the vegetables before serving them in a meal.
What was the MOST likely source of the family’s botulism food poisoning?
The family consumed botulism toxin in the canned green beans.
Botulism food poisoning is a preventable illness if special precautions are taken during food preparation. In this case, what could Sue have done to prevent the outbreak of botulism? Select all that apply.
Sue noticed that the pressure cooker was malfunctioning during the canning process. She should have fixed the instrument, borrowed a properly working one, or purchased a new pressure cooker. Sue could have boiled the food for at least 10 minutes before serving it to her family members.

Which of the following best explains why the pressure cooker is so important in the canning process?
A pressure cooker utilizes steam to create a higher-pressure environment that allows the food to cook at higher temperatures than normal. The higher temperatures kill most contaminating microbes and endospores and therefore effectively sterilize the food.
Use of moist heat can control microbial growth in many circumstances, but heat-sensitive items and those susceptible to moisture cannot be sterilized in this manner. Which of the following correctly describes a method of physical control used to control microbial growth on or in such items? Select all that apply.
Sodium nitrate and sodium nitrite are added to many meat products, such as ham, bacon, hot dogs, and sausage. These additives help to prevent the growth of Clostridium botulinum by inhibiting certain iron-containing enzymes of the organism. This is an example of chemical food preservation. Which of the following correctly describes a method of chemical control used to control microbial growth? Select all that apply.
An antimicrobial chemical was added to a population of bacteria. The initial population was 107 living cells (10,000,000). After 2 minutes, only 106 cells still remained alive. After another 2 minutes (4 minutes of total treatment), about how many cells would still be alive?
Which of the following best describes why microbial death curves are typically plotted logarithmically?
Most of the cell death occurs early in the treatment.
Microbial control methods usually target any of the following microbial structuresEXCEPT which one?