Microbial Growth

Total Flash Cards » 36
Text Size: S | M | L
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. Both organisms would grow, but they would be dyed different colors. Only one organism would grow. Only one organism would grow, and it would grow a different color.
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? It is impossible to distinguish between selective and differential media in this case. selective media differential media general purpose media enrichment media
Which of the following would you expect to be a function of MacConkey agar? Mark all that apply.

allow for the growth of all organisms in a sample regardless of nutritional requirements inhibit the growth of certain bacteria allow for the growth of all organisms in a sample that require only the most common nutrients change the color of some organisms based on their metabolic characteristics
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. The septum splits the replicated chromosomes. The mitotic spindle drives the separation. The nuclear membrane dissolves. 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. 20 minutes No time is needed -- the daughter cells cannot replicate further. After the cells have matured fully. 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
1, 4, 3, 2 3, 1, 2, 4 4, 3, 1, 2 3, 2, 1, 4 2, 4, 3, 1
3, 1, 2, 4
What would happen if the septum did not form during binary fission? The daughter cells would not be genetically identical. Nothing; the septum is not required for binary fission. The chromosome could not replicate. The parent cell would now have two copies of the chromosome. 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? Six Nine Twelve Twenty-four Forty-eight Cannot be determined Twenty-four
What results when a single bacterium reproduces? Two genetically unique daughter cells One parent cell and a genetically identical daughter cell One parent cell and a genetically different cell Two genetically identical daughter cells Two genetically identical daughter cells
If you begin with six cells, how many cells would you have after three rounds of division? Twelve cells Nine cells Eighteen cells Twenty-four cells Forty-eight cells It is impossible to determine. Forty-eight cells
Which of the following is NOT a step in bacterial cell division? Cell elongation Disappearance of nuclear envelope Replication of the genetic material Splitting apart of two new daughter cells Disappearance of nuclear envelope
Which step of binary fission is the reason for genetically identical daughter cells? Replication of the bacterial chromosome Splitting of the two daughter cells There are four new daughter cells that result from one parental cell Elongation of the cell 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. Mesophiles Facultative halophiles Hyperthermophiles Psychrophiles Extremophiles Mesophiles Facultative halophiles
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. Fecal coliforms will not need organic growth factors to grow in the lake environment. The lake environment will support only the growth of obligate anaerobes. The lake environment will support the growth of facultative anaerobes. 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. Fecal coliforms will likely contain enzymes to counteract toxic oxygen forms.
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? colony biofilm planktonic unit infectious unit biofilm
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? complex culture medium anaerobic culture medium basic culture medium enrichment culture medium 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? plate count culture filtration count culture serial dilution count culture direct microscopic counts 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. The bacteria have to establish a biofilm before their numbers can increase. The medium contains inhibitors that prohibit rapid growth of the bacteria, and these must be inactivated before bacterial numbers will increase. There are not enough nutrients for the bacteria to grow, and growth is delayed until there are some dead cells to cannibalize. 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. The number of cells that are dying is balanced by the number of new cells that are being formed. The cells are likely running out of nutrients. The cells are dead; therefore, the number is staying constant. Cells are not increasing in number because they have not yet adjusted to the nutrient availability in the new media. Harmful waste products may be accumulating. The number of cells that are dying is balanced by the number of new cells that are being formed. The cells are likely running out of nutrients. 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. Chemostats include detoxifying agents that inactivate growth-inhibiting toxins that develop during continued microbial growth. Chemostats include growth-promoting agents that prolong microbial growth. Chemostats promote the formation of endospores, which enable the long-term survival of the bacteria. 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 8 million 4 million 2 million 32 million 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? electronic cell counter plate count direct microscopic count Any of these methods will provide reliable data for plotting a growth curve. indirect estimate based on turbidity 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. proteins. phospholipids. DNA and proteins. DNA and phospholipids. DNA and proteins.
Most bacteria reproduce by fragmentation. aerial hyphae. mitosis. binary fission. budding. binary fission.
Which of the following shows the moist heat methods in order of the temperature used (highest to lowest)? Autoclave>Ultrahigh>Batch Pasteurization>Boiling Ultrahigh>Boiling>Autoclave>Batch Pasteurization Ultrahigh> Boiling>Batch Pasteurization >Autoclave Ultrahigh>Autoclave>Boiling>Batch Pasteurization 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; beneficial microorganisms are not killed Pasteurization; the taste of the food or drink will not be altered autoclaving; beneficial microorganisms are not killed autoclaving; the taste of the food or drink will not be altered 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? definitely not probably not yes, most likely 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. Mary microwaves food before putting it on the table. Sue uses bleach to clean the kitchen counters. Mary places leftovers in the refrigerator after the meal. Sue uses bleach to clean the kitchen counters. Mary places leftovers in the refrigerator after the meal. 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 chicken. The family consumed botulism toxin in the canned tomatoes. The family consumed botulism toxin in the canned green beans. The family consumed botulism toxin in the spinach salad. 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 lightly heated the food before serving it to her family members. Sue could have boiled the food for at least 10 minutes before serving it to her family members. She could have discarded all of the home-canned food and replaced it with store-bought canned vegetables. 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 normal atmospheric pressure for longer-than-normal cooking times in order to prevent the growth of microbial contaminants and possible endospores. 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. Pressure cookers utilize temperatures that kill only the pathogenic organisms and leave behind the nonpathogenic ones to enhance the flavor of the food. Pressure cookers utilize pressure and dry heat to create an environment that will remove harmful organisms from the food contents. Dry heat is the most effective method of eliminating endospores. 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. Filtration is the passage of a liquid or a gas through a screenlike material with pores small enough to retain microorganisms. A vacuum is typically used to force the liquid through the mesh, and then the sterile liquid or gas is collected in a sterile container on the other side. Nonionizing radiation, such as UV light, has a wavelength longer than that of ionizing radiation. The wavelengths of UV light are absorbed by cellular DNA in organisms directly exposed to the light. Desiccation is a process that removes water from microorganisms, leaving them unable to grow or reproduce, but still viable. Osmotic pressure is a process that uses high concentrations of salts and sugars to preserve food. Filtration is the passage of a liquid or a gas through a screenlike material with pores small enough to retain microorganisms. A vacuum is typically used to force the liquid through the mesh, and then the sterile liquid or gas is collected in a sterile container on the other side. Nonionizing radiation, such as UV light, has a wavelength longer than that of ionizing radiation. The wavelengths of UV light are absorbed by cellular DNA in organisms directly exposed to the light.
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. Surface-active agents, or surfactants, decrease surface tension among molecules of a liquid. Phenolics exert antimicrobial activity by injuring lipid-containing plasma membranes, which causes the cellular components to leak out of the cell. Alcohols exert their action by denaturing proteins and dissolving lipids. High pressure is used to denature proteins in vegetative cells. Surface-active agents, or surfactants, decrease surface tension among molecules of a liquid. Phenolics exert antimicrobial activity by injuring lipid-containing plasma membranes, which causes the cellular components to leak out of the cell. Alcohols exert their action by denaturing proteins and dissolving lipids.
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? 0 103 104 105 105
Which of the following best describes why microbial death curves are typically plotted logarithmically? Different treatments vary in the length of time required to kill all microbes. Bacterial population sizes are typically expressed in logarithmic form. Most of the cell death occurs early in the treatment. It takes longer to kill all members of a large population than a smaller one. Most of the cell death occurs early in the treatment.
Microbial control methods usually target any of the following microbial structuresEXCEPT which one?
mitochondria nucleic acids plasma membrane permeability microbial proteins
mitochondria