Microbiology Chatpers 5, 6, and 7

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What is an important step in the preparation of a proper bacterial smear?

Allow the loop to cool after it has been flamed

When transferring an inoculum from an agar broth or slant tube to a slide, you should sterilize your inoculating instrument to avoid cross contamination. When should the instrument be heat sterilized with the bunsen burner?

Both before and after transferring the inoculum to the slide.

When transferring an inoculum from a solid medium, it is necessary to resuspend the culture to help avoid cell clumping. In what substance should the cells be resuspended?


Sometimes bacterial cultures suspended in broth culture sediment to the bottom of the broth tube. What technique should be used to resuspend this culture?

gently flick the tube with your finger

When creating a bacterial smear from a broth culture, how many loopfuls of inoculum should be placed onto the slide to ensure that enough bacteria are transferred?

2 or 3 loopfuls

It is necessary to prepare proper bacterial smears before performing which of the following staining techniques?

Gram stain, simple stain, and spore stain

What is the purpose of applying a stain to a bacterial smear?

To provide contrast between the organism and the background

What is the definition of a basic stain?

Stain with a positively charged chromogen

Why are basic stains attracted to the bacteria itself?

Cell wall components carry a negative charge and the chromogen has a positive charge; opposite charges attract one another.

Which of the following is an example of a basic stain?

Methylene Blue

Vibrio cholera is a water-borne pathogen that colonizes the gastrointestinal tract. How would you describe the shape of this organism?

Curved rod

What is the difference between spirilla and spirochetes?

Spirilla are rigid, while spirochetes are flexible

What two characteristics are used to describe the cellular morphology of a microscopic organism?

Shape and arrangement

Why doesn’t an acidic stain adhere to bacterial cells?

Acidic stains have a negatively charged chromogen and are repelled by the negative charges on bacterial surfaces.

What is an example of an acidic stain?

India ink

What are the practical advantages of using a negative staining technique?

Cells retain their natural size and shape, and are not distorted by the effects of chemicals or heat.

Why should negatively stained slides be handled with extra precaution?

The live organisms in the inoculum are not killed with heat fixation.

Step two of the procedure states: "Using sterile technique, place a loopful of inoculum from the M. luteus culture in the drop of nigrosin and mix." What procedure qualifies as sterile technique?

Heat-sterilizing the inoculating instruments before and after transferring the inoculum

What is a difference between an acidic stain and a basic stain?

An acidic stain has a negatively charged chromogen and a basic stain has a positively charged chromogen.

What are the steps of gram staining?

1. Crystal Violet (rinse) 2. Iodine (rinse) 3. Decolorize (rinse) 4. safranin (rinse) 5. blot slide 6. view under microscope

After you add crystal violet to the slide, what should be your next step?

Rinse with distilled water.

After you add crystal violet and rinse the slide, what should be your next step?

Add Gram’s iodine.

After Gram’s iodine is added and then rinsed, what is the next step in the Gram stain procedure?

Add decolorizing agent.

What is the best procedure for decolorization?

Add decolorizing agent until run-off is clear.

What happens to the Gram-positive cell wall during decolorization?

The decolorizing agent dehydrates the peptidoglycan.

What happens to the Gram-negative cell wall during decolorization?

The decolorizing agent dissolves the outer membrane.

As bacterial cells age, their peptidoglycan begins to break apart. What would be the effect on decolorization?

Old Gram-positive cells will be decolorized.

How does safranin affect Gram-positive cells?

Safranin penetrates the cell wall, but not enough of it is retained to cause a color change.

If you FORGOT to do the decolorizing step, what colors would the Gram-positive and Gram-negative cells be when viewed at the end of the procedure?

All would be purple.

You performed the Gram stain on a smear. You are expecting to find purple Gram-positive bacilli and pink Gram-negative cocci. Instead, you observe pink bacilli and pink cocci. What is NOT a possible explanation for this unusual result?

You skipped the safranin step.

You performed the Gram stain. You are expecting to find purple Gram-positive cocci and pink Gram-negative bacilli. Instead, you observe purple cocci but don’t seem to see any bacilli. How could you explain this?

You forgot the safranin step.

What are the characteristics of gram-positive bacteria?

1. many layers of peptidoglycan 2.crystal violet retained during decolorization 3. stains purple

What are the characteristics of gram-negative bacteria?

1. stain red/pink 2. crystal violet is not retained during decolorization 3. one or two layers of peptidoglycan

The Gram stain is an example of a __________ stain, because the process uses two contrasting stains to separate bacteria into groups based on cell wall composition.


While gram-positive cells have a thick layer of __________ in their cell walls, gram-negative cells have a thin layer, surrounded by an additional lipopolysaccharide layer.


What basic stains are used in the Gram staining procedure?

Crystal violet and safranin

What substance is used as a decolorizing agent in the Gram stain?

Ethyl alcohol

If you forget to add the decolorizing agent when performing a Gram stain, what color will the gram-negative cells be?


After performing a Gram stain, gram-negative cells appear __________, while gram-positive cells appear __________.

pink or red; purple

What is the purpose of using Gram’s iodine during the Gram staining procedure?

Gram’s iodine is a killing agent, binds to crystal violet, and serves as a mordant.

Which of the following represents an incorrect association regarding the reagents used during the Gram Staining procedure?

1. counterstain = Methylene blue 2. Mordant = Gram’s iodine 3. Decolorizing agent = Ethyl alcohol 4. Primary stain = Crystal violet Answer #1

While vegetative cells are metabolically _____, cells in the spore form are metabolically _____.

active; inactive

What process is likely to occur when environmental conditions become unfavorable?


The spore is resistant to which of the following extreme environmental conditions?

Extreme temperatures, radiation, and desiccation.

While the formation of the spore is called _____, the reversion to a vegetative cell is called _____.

sporogenesis; germination

What is the purpose of steaming the stain while applying malachite green?

To allow the malachite green to penetrate more deeply into the thick spore coat

Which of the following represents a true statement regarding the structure of the capsule?

The capsule structure protects bacteria from the immune response of the host.

What stain is used as the counterstain when performing a spore stain?


Members of which genus of bacteria are best stained using the acid-fast method?


While __________ bacteria retain carbol fuchsin after acid-alcohol treatment, __________ bacteria are decolorized by acid-alcohol.

acid-fast; non-acid-fast

A thick waxy layer of what substance in the cell wall constitutes the major portion of the mycobacterial cell wall, separating it from other microorganisms?

Mycolic acids (lipoidal)

What color do you expect Escherichia coli to be after performing the acid-fast stain?


What color do you expect Mycobacterium smegmatis to be after performing the acid-fast stain?


What is the purpose of heating the slide during the staining process?

Allows for further penetration of the stain through the lipoidal wall and into the cytoplasm

A new antibiotic is produced that inhibits the synthesis of acetyl-CoA and the electron transport chain in bacteria. For each glucose molecule that is metabolized, how many fewer ATP molecules will be produced?


Based on the concept map only, which of the following is most likely to be true of microbial metabolism?
-The energy from 2 ATP is necessary to drive the electron transport chain.
-The Krebs cycle produces molecules necessary for function of the electron transport chain.
-Acetyl-CoA is produced by substrate-level phosphorylation.
-Acetyl-CoA is converted directly into 2 ATP

The Krebs cycle produces molecules necessary for function of the electron transport chain.

What process produces the most ATP?

the electron transport chain

Why is ATP required for glycolysis?

ATP makes it easier to break apart glucose into two three-carbon molecules.

Glycolysis literally means what?

sugar splitting

How many net ATPs can be made from one molecule of glucose in glycolysis?


What carbon molecules remain at the end of glycolysis?

Pyruvic acid

Which of the following statements about glycolysis is true?
-Glycolysis produces glucose.
-All cells perform glycolysis.
-Glycolysis is the main source of NADH in the cell.
-Glycolysis is also called the Embden-Meyerhof pathway.

Glycolysis is also called the Embden-Meyerhof pathway.

What occurs at the bridge step in the krebs cycle?

Decarboxylation of pyruvic acid

How many electron carriers are reduced in the Krebs cycle only?


What is the function of GTP?

an energy carrier

What is the fate of metabolites during respiration?

They are oxidized completely to carbon dioxide and water.

Where would you expect to find electron transport chains in a prokaryote?

Along the plasma membrane

Which compounds provide electrons to the electron transport chain?


What does oxygen get reduced to at the end of the electron transport chain?


What does the electron transport chain do to the concentration of hydrogen ions (protons)?

The concentration of protons is higher outside the membrane than inside.

The process of generating ATP using a proton gradient is referred to as what?


Which of the following statements about fermentation is true?

-It is an alternative way to return electron carriers to their oxidized state.
-It allows the electron transport chain to continue in the absence of oxygen.
-It provides additional protons to allow the electron transport chain to continue.
-It is an alternative way for a cell to produce oxygen.

It is an alternative way to return electron carriers to their oxidized state.

What is the role of pyruvic acid in fermentation?

It takes the electrons from NADH, oxidizing it back into NAD+.

What is the fate of the NAD+ newly regenerated by fermentation?

It returns to glycolysis to pick up more electrons.

What are the two acids produced by fermentation?

Lactic acid and propionic acid

What is the intermediate product formed by pyruvic acid during alcoholic fermentation?


Which of the following correctly matches enzyme components with their correct definition and/or function?

Coenzymes are the organic cofactors important to enzyme activity.

Which of the following conditions would increase enzymatic activity in a bacterial cell that normally thrives in the human body? and Why?

slightly increasing the temperature within the optimum range *This happens because the molecules are moving faster*

Which of the following is true of aerobic respiration compared to anaerobic respiration? What are some examples?

Aerobic respiration uses oxygen as a final hydrogen acceptor, whereas anaerobic respiration uses an inorganic molecule other than oxygen as the final electron acceptor. Nitrate, sulfate, or carbonate.

Much of the energy released in catabolic reactions is captured in ATP for use in other reactions. When the phosphate is transferred directly from an organic molecule to ADP in order to produce ATP, as represented by C–C–C ~P + ADP → C–C–C + ATP, this represents __________.

substrate-level phosphorylation

What is substrate-level phosphorylation?

When phosphate is transferred from a substrate to ADP

When proteins are oxidized, all of the following are true EXCEPT which one?

-The amino group is removed through deamination and converted to nitrogenous waste such as NH4+.
-Enzymes break down proteins into component amino acids.
-Microbes produce extracellular enzymes to reduce proteins to their fatty acid and glycerol components so that each component can enter the Krebs cycle.
-After deamination of the protein, the organic acid enters the Krebs cycle.

Microbes produce extracellular enzymes to reduce proteins to their fatty acid and glycerol components so that each component can enter the Krebs cycle. *This is not true of protein oxidation but it is true of lipid oxidation.*

Microbes are often identified using biochemical tests that detect specific enzymes of metabolic pathways. E.coli typically ferments lactose, whereas the dysenterybacterium, Shigella, does not. If a pure culture of each bacterium were placed in a tube containing lactose as the only food source, and a chemical indicator changed color if the tube became acid, what would the tubes look like after the bacteria were incubated?

The tube with E. coli would indicate a pH change, and the Shigella tube would indicate no change. *This biochemical test is used to differentiate E. coli, which produces lactase and ferments the sugar (thereby producing acids), from Shigella, which does not produce lactase.*

Which of the following pairs is mismatched?

-RNA polymerase makes a molecule of RNA from an RNA template
-DNA gyrase coils and twists DNA
-transposase insertion of DNA segments into DNA
-DNA ligase joins segments of DNA
-DNA polymerase makes a molecule of DNA from a DNA template

transposase insertion of DNA segments into DNA

DNA is constructed of

two strands of nucleotides running antiparallel.

What is not a product of transcription?

a new strand of DNA

Culture 1: F+, leucine+, histidine+
Culture 2: F-, leucine-, histidine-

In the table, if culture 1 mutates to Hfr, what will be the result of conjugation between the two cultures?

1 will remain the same; recombination will occur in 2

An enzyme produced in response to the presence of a substrate is called a what?

inducible enzyme.

Transformation is the transfer of DNA from a donor to a recipient cell

as naked DNA in solution.

According to the operon model, for the synthesis of an inducible enzyme to occur, what must happen?

substrate must bind to the repressor.


In the figure, if base 4 is thymine, what is base 4′?


UUA leucine UAA nonsense
GCA alanine AAU sparagine
AAG lysine UGC cysteine
GUU valine UCG, UCU serine

Refer to the table The anticodon for valine is


UUA leucine UAA nonsense
GCA alanine AAU sparagine
AAG lysine UGC cysteine
GUU valine UCG, UCU serine

Refer to the table. What is the sequence of amino acids encoded by the following sequence of bases in a strand of DNA?


Translation would stop at the first codon.

The necessary ingredients for DNA synthesis can be mixed together in a test tube. The DNA polymerase is from Thermus aquaticus, and the template is from a human cell. The DNA synthesized would be most similar to

Human DNA.

An enzyme that copies DNA to make a molecule of RNA is

RNA polymerase.

Assume the two E.coli strains shown below are allowed to conjugate.

Hfr: pro+, arg+, his+, lys+, met+, ampicillin-sensitive
F: pro-, arg-, his-, lys-, met-, ampicillin-resistant

What supplements would you add to glucose minimal salts agar to select for a recombinant cell that is lys+, arg+, amp-resistant?

ampicillin, proline, histidine, methionine

Protein synthesis in eukaryotes is similar to the process in prokaryotes in that both eukaryotes and prokaryotes

use codons to determine polypeptide sequences.

What observations would best suggest that a plate was inoculated with a pure (axenic) culture?

The unknown culture contains two species of bacteria. Bacterial species tend to produce distinctive-looking colonies. If all colonies on the plate appear identical, then it’s likely the inoculum was pure.

Imagine that you forgot to flame the loop before streaking the inoculum from the first quadrant into the second quadrant. What is the most likely consequence of this error?

Too much bacterial growth outside the first quadrant. Proper streak plating technique deposits progressively smaller amounts of bacteria in each quadrant. This is done by having the loop pick up only a small amount of bacteria from the previous quadrant’s streaks. Flaming the loop between streaks ensures that the loop starts clean and that only this small amount of bacteria is used to inoculate the next quadrant.

What is the correct way to open a petri plate?

Lifting the lid of the Petri plate only enough to get the loop inside keeps the agar protected. Most of the lid remains right above the agar, and this prevents airborne microbes from falling into your culture.

Where should you label your Petri plate with information about the culture? and why?

All labeling should be done on the bottom portion of the agar plate. This ensures that the written information stays with your culture, even if the lid gets accidentally exchanged with another plate.

What are the steps for streaking a petri plate?

1. flame the loop and let it cool 2. lift the lid of the petri plate 3. streak across streak a and into quadrant 2 4. streak within quadrant 2 5. close the petri plate lid 6. rotate plate and flame the loop

If a correctly streaked plate were INCORRECTLY incubated right side up (instead of upside down), what would you expect to see?

During incubation, water tends to condense in the lid of Petri plates. If the plate is incubated in a right-side-up position, this condensation will "rain" onto the surface of the agar. The water on the agar will create a soupy mess of bacteria instead of isolated colonies. Incubating the plate upside down keeps water condensation in the lid and away from your culture.

What would expect to see if an air borne contaminate was exposed to a petri plate?

When a plate is exposed to airborne contaminants, the contaminating microbes settle all over the plate. After incubation, the colonies from these contaminants will be all over the plate also, not just following the streak lines.

What kind of diets can bacteria live on?

Carbon dioxide, iron, sulfur, hydrogen gas, and ammonia

What chemical reactions produces energy? What is another name for these reactions?

catabolic reactions degradative reactions

What chemical reactions use energy?
What is another name for these reactions?

anabolic reactions biosynthetic reactions

What is metabolism?

the sum of all chemical reactions within a living organism

What is catabolism?

the breakdown of complex organic compounds into simpler ones.

What is a hydrolytic reaction?

reactions which use water and in which chemical bonds are broken

What is exergonic?

produce more energy than they consume

What is an example of a catabolic reaction?

breaking down sugars into water and carbon dioxide

What is anabolism?

building of complex molecules from simpler ones.

What is dehydration synthesis reactions?

reactions that release water while molecules are being made

What is endergonic?

consume more energy than they produce

What is an example of anabolic processes?

formation of proteins from amino acids, nucleic acids from nucleotides, and polysaccharides from simple sugars.

What do biosynthetic reactions generate?

materials for life

What makes up ATP?

adenine, ribose, and 3 phosphate groups

When do chemical reactions occur?

when chemical bonds are broken or formed

What is activation energy?

collision energy required for a chemical reaction

What is a catalyst?

substances that can speed up a chemical reaction without being permanently altered

What is reduced?

electron acceptor/oxidizing agent

What is oxidized?

electron donor/reducing agent

What is oxidation?

the removal of electrons

What is reduction?

the gain of electrons

If you have a lot of hydrogens what else do you have a lot of?


What is dehydrogenation?

removing hydrogen and electrons

True or false. A cell can do any chemical reaction with or without enzymes.

false; enzymes are required for chemical reactions to occur

The amount of molecules you can make is what?

turnover number

What is an apoenzyme?

an inactive enzyme

What is a cofactor?

a substance whose presence is essential for the activity of an enzyme.

What is a coenzyme?

a nonprotein compound that is necessary for the functioning of an enzyme.

What are the electron carriers?

NAD+, NADP+, FAD, and CoA

What do the electron carriers help with?

The help with the production of ATP

What do the inhibitors do to enzymes?

the prevent the enzyme from working

What happens when something is denatured?

the break down of hydrogen bonds and other covalent bonds

What make up enzymes?

the 20 amino acids

What do all organisms use to make proteins?

amino acids

How do enzymes increase speed?

they lower the activation energy

What causes the tertiary protein structure?

all the different attractions

True/False Carbon fixation occurs during the light-independent phase of photosynthesis.


Which organism is NOT correctly matched to its energy source?

1. chemoautotroph – Fe2+
2. chemoheterotroph – glucose
3. photoautotroph – CO2
4. chemoautotroph-NH3
5. photoheterotroph – light

photoautotroph – CO2

Which of the following has bacteriochlorophylls and uses alcohols for carbon?

1. photoautotroph
2. chemoautotroph
3. photoheterotroph
4. chemoheterotroph


Streptococcus lacks an electron transport chain. How does this bacterium reoxidize NADH? Where is the NADH formed?

Streptococcus goes through fermentation. From each molecule of glucose 2 molecules of ATP and two molecules of NADH are formed. The NADH is deoxidized in fermentation when the electrons are given to pyretic acid to be reduced to lactate.

Which of the following statements about beta oxidation is false?

1. It is used in petroleum degradation.
2. It is a step in glycolysis.
3. It is a method of catabolizing fatty acids.
4. It involves the formation of 2-carbon units.
5. It involves the formation of acetyl-CoA.

It is a step in glycolysis.

NO3-+ 2H+ NO2- + H2O
Nitrate ion Nitrite ion

Which of the following is true about this reaction?

1. This process requires O2.
2. This process requires the electron transport system.
3. This process requires light.
4. This process occurs anaerobically.
5. This process requires O2 and the electron transport system.

This process occurs anaerobically.

If a cell is starved for ATP, which pathway would most likely be shut down?

pentose phosphate pathway

In noncyclic photophosphorylation, O2 is released from what?


What is NOT necessary for respiration?


True/False Both respiration and photosynthesis use water molecules for the donation of hydrogen ions.


Assume you are working for a chemical company and are responsible for growing a yeast culture that produces ethanol. The yeasts are growing well on the maltose medium but are not producing alcohol. What is the most likely explanation?

O2 is in the medium.

True/False The pentose phosphate pathway can be characterized as an anabolic pathway.


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?

48 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

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?


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?

Mesophiles, Psychrophiles, Facultative halophiles The bacterial growth process depends on the microorganism’s ability to adapt to environmental conditions. Being able to grow to larger numbers increases the chances for survival and spread to new hosts. Requirements for growth have led us to develop descriptive terms for the organisms that refer to temperature range [Chapter 6, section 6-1], pH range [Chapter 6, section 6-2], and pressure range [Chapter 6, section 6-3].

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?

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. With chemical and physical requirements met, bacteria are able to replicate in their environment and potentially increase numbers enough to find or invade a new host.

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?

biofilm Biofilms are a large collection of mixed populations of organisms that form a matrix of "slime" for protection and assemble a complex, coordinated, and functional community on a surface. Biofilms often provide a safe haven for bacterial growth, often among "friendly" microorganisms. The complex architecture of biofilms gives the cells benefits they would not have in an individual lifestyle as a planktonic cell. As such, biofilms can play an extremely important role in colonizing a host and leading to a disease state.

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 Growth of microorganisms for identification is not a trivial exercise. To accurately and efficiently grow bacteria in culture, you must consider the bacteria’s relative abundance, metabolic and chemical needs, and best growth conditions, as well as the cost and overall goals of the experiment. Enrichment culture medium is a good choice for environmental samples whose desired populations are low compared to the rest of the microbes present. From a sample of large numbers of organisms, complex medium favors the growth of only certain organisms.

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 *This method will trap organisms and keep them on the surface of the filter. Transferring the organisms to a plate will then produce an accurate count. Fecal coliform bacteria were counted by direct filtration CFUs. Some of the samples taken at the beaches exceeded the recommended maximum levels established by the Environmental Protection Agency (EPA) for direct sampling: greater than 235 E. coli per 100 ml of water, or a geometric mean of greater than 126 E. coli per 100 ml of water. The beach samples were 178.2 E. coli per 100 ml and 1299.7 E. coli per 100 ml, with a geometric mean of 173.2 E. coli per 100 ml.*

Which of the following methods used to count microbes is correctly matched as direct or indirect?

filtration–direct method A specific volume of fluid is filtered through a membrane, which is then placed on media and allowed to grow, representing a direct count of the viable cells.

Which of the following phases of the bacterial growth curve is matched with the correct definition?

log phase–the phase where organisms are actively dividing and the generation time is constant

A microbe reproduces by binary fission every 20 minutes under favorable conditions. How long would 10 generations take and how many bacteria would be present if all the conditions were just right?

3 hours 20 minutes, producing 1,024 bacteria The organism produced 210 over 10 generations, which would take a little over 3 hours and produce over a half million bacterial cells.

Which process is best for the short-term storage of bacterial cultures?

refrigeration Refrigeration is the best short-term storage method for microbes. Refrigeration slows down metabolic activity, but the microbes can be quickly revived at optimum temperatures.

Bacteria that can grow in the presence or absence of oxygen (O2) are called __________.

facultative anaerobes Facultative anaerobes are able to use oxygen if it is present but also to grow in the absence of oxygen, although with decreased efficiency.

Which level of biosafety (BSL) is appropriate for handling organisms that present a moderate risk of infection?


What types of microbes would a microbiologist use culture techniques for living host cells?

obligate intracellular organisms, such as chlamydia and viruses These organisms cannot grow on media but require living host cells when cultured.

What statement accurately describes the culture media necessary for growing Clostridium tetani?

Reducing media are complex media containing chemicals, such as thioglycolate, that combine with oxygen, creating an anaerobic environment.

Microbes have very narrow optimum temperature ranges. What classification of microbes are most likely to cause human disease, based on temperature requirements?

mesophiles The temperature range of mesophiles overlaps that of normal human body temperature, allowing the greatest growth.

What statement regarding infections involving biofilms is FALSE?

There is no way to prevent biofilms from developing on surfaces.

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. 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.

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.

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.

This activity asks you to calculate the size of a bacterial population during exponential growth.
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 *There would be approximately 16 million cells. In the 2-hour interval of log growth, there are four 30-minute generations. This is four doublings of the 1 million organisms present at hour 2. 1 million cells x 24 = 16 million cells*

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

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

facultative halophiles

Nitrogen-fixing bacteria, such as cyanobacteria, can use atmospheric nitrogen (N 2 ) for their nitrogen source.


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?


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


Which of the following is an organic growth factor?

vitamin B1

The source of nutrients in nutrient agar is

peptone and beef extract.

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


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


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.

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


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.


Pathogenic bacteria isolated from the respiratory or intestinal tracts of humans are what?

capnophiles that grow best in carbon dioxide incubators.

What is the difference between a disinfectant and an antiseptic?

Disinfectants are used on inanimate objects, antiseptics are used on living tissue.

Why must you consider the pH of the location you plan to treat with a disinfectant?

The pH may alter the interaction between the disinfectant and the microbe. The pH may alter the potency of the disinfectant. The pH may alter the susceptibility of the microbe.

You have a spill in the lab, contaminating the benchtop with an organism that is very naturally resistant to disinfectants. How might you increase the potency of the disinfectant you use?

Increase the concentration of the disinfectant

Which of the following is most resistant to disinfectants?

-Gram-positive bacteria
-Bacterial endospores

Bacterial endospores

Which of the following is NOT an environmental condition that needs to be considered when selecting a disinfectant?

-Length of exposure
-Type of material to be disinfected

The lab tests often involve lots of bacteria growing on nutrient agar; nutrient agar is rarely disinfected in reality.

Why are the tests performed in the lab not always a good indicator of how effective a disinfectant will be in the real world?

The lab tests often involve lots of bacteria growing on nutrient agar; nutrient agar is rarely disinfected in reality.

Which chemical is best to use for disinfection regardless of the environmental or microbiological conditions?

-Hydrogen peroxide
-None of the available answers are correct.

None are correct

Since longer exposures to disinfectants result in better disinfection, why don’t we just disinfect everything we need to for a minimum of 5 days?
-Long exposures could begin to adversely affect delicate objects.
-This may increase the probability of someone being exposed to the harsh disinfectants.
-This is impractical financially.
-All available answers are correct.

All are correct

What is an antibiotic?

A chemical that inhibits microbial growth

What does the Kirby-Bauer test assess?

The susceptibility of an organism to a set of antibiotics

Which of the following best describes what a single Kirby-Bauer plate is testing?
-Do different antibiotics diffuse the same distance through agar?
-Is a particular bacterium susceptible to any of a variety of antibiotics?
-Are a variety of bacteria susceptible to a single antibiotic?
-All available answer choices are possibilities.

Is a particular bacterium susceptible to any of a variety of antibiotics?

What characteristic of the Kirby-Bauer test helps scientists to determine if a microorganism is susceptible to an antibiotic?

The diameter of the zone of inhibition surrounding the antibiotic disks

What is a zone of inhibition?

The area around the antibiotic disk in which bacteria cannot grow

Which of the following characteristics does NOT need to be standardized in a Kirby-Bauer assay?

The method used to develop a bacterial lawn on the agar plate

Why is it critical to use aseptic technique when transferring the antibiotic disks to the agar?

-Contaminating microorganisms could break down the antibiotics.
-Contaminating microorganisms could alter the diffusion of the antibiotics through the agar.
-Contaminating organisms could produce their own antibiotics.
-All available answers are correct.

All are correct

What are the three possible outcomes for each antibiotic: microorganism pair in a Kirby-Bauer assay?

Susceptible, resistant, or intermediate

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