micro ch 6

A sample is collected and grown in Luria broth overnight. There are three different species of bacterium growing in the broth. The sample is transferred to Luria agar. How many different types of colonies would you expect to see on the agar after growth. 1 2 3 4 Too many to count

3

Select the incorrect statement. A total direct cell count includes the counting of live cells. A total direct cell count includes the counting of dead cells. A total direct cell count involves the measuring the turbidity of a liquid culture using a spectrophotometer. A total direct cell count is conducted by counting the cells in several grid squares and then calculating the average density.

A total direct cell count involves the measuring the turbidity of a liquid culture using a spectrophotometer.

What are the advantages and disadvantages of growing in an oxygen-rich environment?

Oxygen, which is an avid acceptor of electrons, enables organisms to extract more energy from compounds via oxidative phosphorylation than can be extracted using any other terminal electron acceptor.

Select the incorrect statement. Complex media are derived in part from components where the specific concentrations of each nutrient are unknown. Examples of complex media include media formulated from crude yeast or animal (beef or brain) extracts. In defined media, the chemical identity and concentration of all components are known. In defined media, yeast, animal, and plant tissue is present. None of these choices are incorrect.

In defined media, yeast, animal, and plant tissue is present.

How is temperature used to eliminate microbes or control their growth? Most, but not all, microorganisms can be killed by elevating the temperature 100 °C (boiling). Some microbes, however, produce spores that are resistant to temperatures. Most common pathogens can be removed from milk or juice by brief heating to temperatures below boiling (a process called pasteurization). This process is widely used because it kills most pathogens while preserving the properties of the liquid, however many bacteria are not destroyed during this process and pasteurized milk or juice will spoil after prolonged storage. Refrigeration is used to impede the growth of microbes and can preserve specimens, food or media for extended periods whereas, freezing stops the growth of almost all microbes for indefinite periods and is an excellent way to preserve food or specimens for long term storage. All of these choices are correct.

All of these choices are correct.

What are the advantages and disadvantages of removing microbes by filtration? Removing microbes from media or other fluids by filtration is fast. Filtration does not involve heating or chemically treating the sample, which in some cases is critical if components in the media are sensitive to heat or it is undesirable to add chemicals. Filters have the disadvantage of being expensive. Filters are easily clogged by particles in the solution. Viscous liquids display very poor flow rates through most filters. All of these choices are correct.

All of these choices are correct.

What roles do ions play in cells? Ions such as K+, Na+ and Cl- play an important role in controlling osmotic balance within the cell. Mg2+ and Mn2+ are critical for the function of DNA polymerases, and Mg2+ is also important for other types of protein-nucleic acid interaction. Iron is the central factor that enables enzymes such as cytochromes to carry and shuttle electrons. Other less abundant ions are needed as cofactors for enzymes that are present in low levels in the cells (and hence are called micronutrients since only very small amounts of such ions are needed for growth). Ions that are micronutrients include Zn2+, Co2+, Mo+, Cu2+, and Mn2+. All of these choices are correct.

All of these choices are correct.

Often times, when microorganisms are extracted from the environment, it is difficult to grow them in a culture in the laboratory. Why might this be? The nutrients required for this microorganism are unknown. The cofactors required for this microorganism are unknown. The microorganism may be sensitive to nutrients in the media. The nutrients and cofactors are available but the organism is incubated at the incorrect temperature. All of these could be true.

All of these could be true.

From what sources can organisms acquire electrons? All organisms require electrons to use as reducing agents for biochemical oxidation and reduction reactions. Organotrophs acquire electrons by breaking down organic molecules, such as glucose. Lithotrophs remove electrons from inorganic reduced molecules, such as ferrous iron (Fe2+), elemental sulfur, hydrogen gas (H2), hydrogen sulfide (H2S), ammonium (NH4+), and nitrite (NO2-). None of these statements is correct. All of these statements are correct.

All of these statements are correct.

How might understanding the natural growth requirements of a microorganism help a researcher? It is essential for its cultivation. It is important to understand the natural environments in which the organism can thrive (or fail to thrive). We can make predictions based on what the organism can and cannot grow on, as to what metabolic pathways are present in the cell. None of these statements is correct. All of these statements are correct.

All of these statements are correct.

What is a continuous culture? Continuous culture systems (e.g. chemostats) are open systems in which nutrients are fed into a culture vessel at a constant rate. The volume of the culture is kept constant by draining the excess medium (including cells and waste) at the same rate as fresh media is introduced. Continuous culture systems allow the density of the culture to be controlled by the concentration of nutrients in the media while the growth rate of the culture is controlled by the rate at which fresh media is introduced into the system (the dilution rate). Unlike batch cultures, which undergo lag, log, stationary, and death phases, continual culture systems can keep the bacterial culture growing in the log phase for indefinite period of time. All of these statements are correct.

All of these statements are correct.

Which of the following cellular components or processes are affected by temperature changes? Temperature affects the rate of chemical reactions by affecting the thermal energy of molecules, making them more or less likely to react if the temperature goes up or down, respectively. Temperature affects the folding and conformation of proteins, which can have dramatic effects on whether a particular enzyme can adopt the conformation necessary to carry out its function. The fluidity of the membrane bilayer also is strongly affected by temperature. Membranes with a large percentage of unsaturated lipids, which pack loosely, will remain more fluid at low temperatures than membranes rich in saturated lipids, which pack together more closely. All of these statements are correct. None of these statements is correct.

All of these statements are correct.

Autotrophs can assimilate carbon from inorganic sources such as carbon dioxide (CO2) whereas heterotrophs must obtain usable carbon from pre-existing organic molecules such as amino acids, lipids, sugars, nucleic acids or smaller organic molecules like pyruvate or acetate.

Autotrophs can assimilate carbon from inorganic sources such as carbon dioxide (CO2) whereas heterotrophs must obtain usable carbon from pre-existing organic molecules such as amino acids, lipids, sugars, nucleic acids or smaller organic molecules like pyruvate or acetate.

What is true when comparing the spread plate and the streak plate method. Both methods spread bacteria over the surface of the plate so that individual colonies can be identified Both methods require dilution of the sample before inoculation onto the plate Both methods are capable of quantifying the number of bacteria in the sample Both methods isolate individual colonies Both methods spread bacteria over the surface of the plate so that individual colonies can be identified and both methods isolate individual colonies

Both methods spread bacteria over the surface of the plate so that individual colonies can be identified and both methods isolate individual colonies

You have completed a direct count of two broths. Broth A has 500 cells/ml and broth B has 1,000,000 cells/ml. What is true about these broths? Broth A will cause more light to scatter when read in a spectrophotometer. Broth B will have a higher optical density. Broth A will have a higher optical density. Broth A will cause more light to scatter when read in a spectrophotometer and Broth A will have a higher optical density.

Broth B will have a higher optical density.

Escherichia coli is inoculated in tryptic soy broth and grows well overnight. Please indicate which statement is NOT true. All of the nutrients required for E. coli growth are available. When agar is added to tryptic soy broth, E. coli will still grow. Colonies can be identified from the tryptic soy broth grown overnight. Other bacteria with the same nutrient requirements will grow in the tryptic soy broth.

Colonies can be identified from the tryptic soy broth grown overnight.

You have extracted a Gram-negative organism from a sample but want to determine if it is a coliform (these are indicative of fecal contamination). Coliforms are Gram-negative microorganisms that characteristically ferment lactose. What type of media might you use to determine whether your unknown organism is a coliform? Selective media Differential media Enrichment media Any of these would be fine

Differential media

Select the incorrect statement regarding selective and differential media. A selective medium is designed such that only one type or a few types of microorganism will grow on it while most other microorganisms will not. An example of a selective medium is one that contains antibiotics that kill off most bacteria but allow the resistant bacteria to grow. This includes the cultivation of Neisseria on Thayer Martin media, which contains a combination of antibiotics that kill most fungi, Gram-positive and Gram-negative bacteria but to which Neisseria is resistant. Differential media allows the growth of more than one type of organism, but will permit the identification of specific species based on visual phenotypes such as a change in the color of the medium. MacConkey medium is actually both a selective and a differential medium because it contains bile salts that prevent the growth of many types of bacteria including Staphylococcus aureus. Differential media like MacConkey, allows the cultivation of both Salmonella and E. coli - but E. coli, which can ferment fructose, will form orange colonies on the agar due to the drop in pH via acid production whereas Salmonella will produce red colonies. All of these statements are correct.

Differential media like MacConkey, allows the cultivation of both Salmonella and E. coli - but E. coli, which can ferment fructose, will form orange colonies on the agar due to the drop in pH via acid production whereas Salmonella will produce red colonies.

A single colony contains approximately 1 billion cells before visible to the naked eye. True False

False

Colonies will be located both on the surface and emedded in the agar when completing the streak plate method. True False

False

During the streak plate method, where would one find isolated colonies after incubation has occurred? First section Second section Third section Last section

Last section

You are trying to quantify the number of microorganisms in an environment where their population density is very low. You filter your sample and quantify on solid media. Why is the direct cell count not a reliable option for quantification? Little to no cells would be seen, making the count unreliable. Too many cells would be seen, making the count unreliable. The bacteria are too little to see with this method. The bacteria might have died and therefore the count would not be reliable.

Little to no cells would be seen, making the count unreliable.

This media can be used for lactose fermentation differentiation and selection for Gram-negative bacteria. Blood agar (BAP) TSA PEA MacConkey agar

MacConkey agar

You are going to prepare an infectious dose of bacteria to run an experiment. This means you need a known concentration of bacteria that is capable of causing disease in your animal model. You complete a total direct cell count. Is this an accurate count? Yes, all living bacteria are counted that will allow for quantification of the infectious dose. Yes, all living and dead bacteria are counted that will allow for quantification of the infectious dose. No, the all living and dead bacteria are counted and will thus not allow for the quantification of the infectious dose. No, quantification is not possible with this method to determine the infectious dose.

No, the all living and dead bacteria are counted and will thus not allow for the quantification of the infectious dose.

Which of the following is not a practical issue that must be considered when using disinfectants? What types of microbes need to be destroyed in the sample? Not all disinfection methods work on all types of microbes. How many microbes are in the sample which needs to be destroyed? Samples containing a lot of microbes it may require more harsh methods to disinfect. What kind of object (e.g., liquid, surface, container) is it that needs to be disinfected? Some objects can be destroyed by certain methods of disinfection. Will the object be eaten or used by animals or humans after disinfection? If so then some chemical disinfectants that are toxic to animals should be avoided. None of these choices.

None of these choices.

How do oxidizing agents affect microbes?

Oxidizing agents including peroxides, bleach, iodine, chlorine and ozone all work by stripping electrons away from proteins, nucleic acids, lipids and cell walls.

How do prototrophic and auxotrophic organisms differ?

Prototrophs can synthesize all necessary cellular constituents from a single organic carbon source and inorganic precursors. Auxotrophs, in contrast, require that at least one organic precursor molecule be obtained from the environment. As a result, auxotrophs will only grow in niches where the appropriate organic molecules can be found.

A streak-plate method is used to isolate colonies of a particular bacterium. In which quadrant are you most likely to find the least number of colonies? Quadrant 1 Quadrant 2 Quadrant 3 Quadrant 4 The number of colonies will be the same in all quadrants

Quadrant 4

Why does growing in a salty environment pose a challenge? Salty environments pose a challenge to cellular life both because of the osmotic stress it places on the cell (in a salty environment we would expect much the water in the cell to escape to the outside). Water has more activity (e.g., of the water that remains, more is available due to the interaction of water with the ions) in a salty environment. Water contains strong hydrogen bonds that allows more of it to interact with the ions. All of these statements are correct. None of these statements is correct.

Salty environments pose a challenge to cellular life both because of the osmotic stress it places on the cell (in a salty environment we would expect much the water in the cell to escape to the outside).

As a microbiologist, you are trying to grow a pure culture of Salmonella typhimurium in broth so you can continue your research on this pathogen. What type of broth might you use to ensure only S. typhimurium will be present in your broth. Selective media Differential media Enrichment media Selective media and Differential media

Selective media

Mannitol salt agar contains two key ingredients to grow Staphylococcus aureus. It contains the sugar mannitol which S. aureus is able to ferment but other Staphylococcus species cannot and it contains a high salt concentration which limits the growth of many different organisms. This media is: Selective media Differential media Enrichment media Selective media and Differential media

Selective media and Differential media

What statement is true when comparing the following medias. Differential media inhibits the growth of certain microorganisms while enrichment media allows the growth of microorganisms Both selective and enrichment media inhibits the growth of certain microorganisms Enrichment media is a type of differential media Selective media inhibits the growth of certain microorganisms while enrichment media allows the growth of microorganisms and enhances the growth of certain microorganisms

Selective media inhibits the growth of certain microorganisms while enrichment media allows the growth of microorganisms and enhances the growth of certain microorganisms

This type of media is used to grow pure cultures. Liquid media Solid media Broth Dry media

Solid media

Select the correct statement. Low population densities will result in high OD readings. High population densities will result in low OD readings. A spectrophotometry is a direct method technique. Spectrophotometers measure the turbidity of a sample

Spectrophotometers measure the turbidity of a sample

Select the incorrect statement regarding the parts of a typical bacterial growth curve. Bacteria that have been taken from spent media and have ceased to grow do not resume growth immediately upon inoculation into fresh media. Instead the culture will have a "lag phase" where the cells adjust their metabolism and protein/lipids to adapt to rapid growth. After exiting lag phase, the cells gradually enter "log phase" or "exponential phase" where growth of the culture reaches the maximum value for that particular condition. Under this condition the rate of growth is exponential because once cell produces two new cells with each cell division. The cells in the culture eventually consume enough nutrients in the culture that the concentration of one or more of the nutrients will be too high to support the maximal growth rate. Also, waste products that may be detrimental to growth (acidic or basic compounds, for example) can build to toxic levels. At this point the growth of the culture slows until it enters "stationary phase". This phase in the growth curve results in no new biomass or new cells being formed (i.e. bacterial growth has stopped). After an extended period in stationary phase a large number of cells in the culture lose viability and will not resume growth when transferred to fresh media (the "death phase"). The loss of cellular viability is likely due to an inability to repair damaged membranes and macromolecules. None of these choices are incorrect.

The cells in the culture eventually consume enough nutrients in the culture that the concentration of one or more of the nutrients will be too high to support the maximal growth rate. Also, waste products that may be detrimental to growth (acidic or basic compounds, for example) can build to toxic levels. At this point the growth of the culture slows until it enters "stationary phase". This phase in the growth curve results in no new biomass or new cells being formed (i.e. bacterial growth has stopped).

Differential media can used to distinguish among the different types of hemolytic activity. True False

True

How can we determine the growth rate of a microorganism? b) Growth of a culture of microorganism occurring in the log phase can be determined by knowing the starting population of cells in the culture (N0, measured at time "0") and the population of cells at a later time (Nt, measured at time "t"). True False

True

Media is used to culture microbes in the lab setting. True False

True

Microbial population densities can be measured using a spectrophotometer. True False

True

Selective, differential, and enhancement media are mechanisms to alter the growth of microorganisms in media. True Fals

True

The most common method is to count the number of colony forming units (CFU) present in a sample. This is typically done by making several serial dilutions of the culture to be tested (for example a 1/10 dilution, a 1/100 dilution, a 1/1000 dilution) and spreading a defined volume of each dilution on its own nutrient agar plate. At some dilution the number of colonies that appear on the plate will be of a sufficient number to be counted accurately (less diluted samples will give too many colonies to count accurately and more dilute samples either give no colonies or too few colonies to be meaningful). Each colony on the plate started as a single cell, therefore, we can make a simple calculation to get back to the concentration of cells (CFU per mL) in the original sample based on the number that we count on the plate. Variations of this method include using filtration to capture microbes present in very dilute samples. Placing the filter on solid media allows colonies to grow and be counted. True False

True

True or false. A spread plate differentiates between living and dead cells when quantifying the number of organisms in contrast to the direct cell count which quantifies both living and dead organisms together. True False

True

A researcher wants to quantify how many microorganisms are present in a broth after it has been exposed to UV light. The broth is grown overnight. What method of inoculation might be most appropriate to quantify the number of living organisms in the broth? Streak plate method Spread plate method Pour plate method Two of these choices are correct All of these choices are correc

Two of these choices are correct

This method involves dilution of the sample prior to inoculation. Streak plate method Spread plate method Pour plate method Two of these choices are correct All of these choices are correct

Two of these choices are correct

Pure cultures can be obtained by: streaking the mixture of bacteria on solid media in a petri dish. If properly performed the sequential streaking of an initial mixture of bacteria onto different sections of the petri dish will result in single colonies of bacteria that are spatially separated from one another. Each colony arises from a single cell that underwent several rounds of cell division. spreading several dilutions of bacteria containing liquid onto plates of solid nutrient media one is able to isolate single colonies that grow. diluting the bacteria into molten nutrient agar at a temperature that should not kill the bacteria and rapidly pouring a plate from this mixture. The pour plate method is best for isolating individual, non-overlapping colonies but is the most laborious and can kill some of the bacteria if the temperature is not well controlled or if the bacteria is particularly heat sensitive. all of these statements are correct. none of these statements is correct.

all of these statements are correct

The advantages of measuring turbidity include _____. getting an instant estimation of the number of cells present in a sample rapid performance of the method (counting colonies can take days or weeks depending on how rapidly the bacteria grow) sampling a culture many times with a spectrophotometer without having to otherwise perturb the culture for analysis (e.g., making dilutions and plating on solid media) all of these statements are correct none of these statements is correct

all of these statements are correct

All of the following are types of special purpose media except: enrichment selective differential general purpose

general purpose

Unculturable microorganisms can be characterized by determining the types of bacteria present in a sample by: isolating DNA from all cells and amplifying and sequencing the 20S ribosomal DNA. isolating DNA from all cells and amplifying and sequencing the 60S ribosomal DNA. isolating DNA from all cells and amplifying and sequencing the 16S ribosomal DNA. isolating RNA from all cells and amplifying and sequencing the 16S ribosomal RNA. isolating RNA from all cells and amplifying and sequencing the 20S ribosomal RNA.

isolating DNA from all cells and amplifying and sequencing the 16S ribosomal DNA.

Media used to grow microorganisms can be in _____. liquid form gaseous form solid form liquid and solid forms solid and gaseous forms

liquid and solid forms

An organotroph is an organism that uses organic molecules as a source of energy. uses organic molecules as a source of electrons. uses organic molecules as a source of carbon. all of these choices.

uses organic molecules as a source of electrons.