Deck 4: Dynamics of Microbial Growth

Question 1

In nature, bacteria

A) seldom grow in close association with many other kinds of organisms.
B) always go through a very short exponential phase.
C) occasionally synthesize structures such as slime layers.
D) may adhere to surfaces by means of pili and slime layers.
E) All of the answer choices are correct.

Answer 1

D

Question 2

A pure culture in exponential growth phase has a bacterial concentration of 6.4 × 10⁸ cells/ml. If the bacterium has a generation time of 1 h, how long ago was the cell concentration 8.0 × 10⁷ cells/ml?

A) 1 h
B) 2 h
C) 3 h
D) 4 h
E) 24 h

Answer 2

C

Question 3

The lag phase of the bacterial growth curve is marked by

A) a decrease in cell mass.
B) dormant, metabolically inactive cells.
C) metabolically active cells.
D) vigorously dividing cells.
E) spore-forming cells.

Answer 3

C

Question 4

During which phase of the bacterial growth curve does a bacterial population become much more resistant to harmful conditions?

A) Lag phase
B) Exponential phase
C) Stationary phase
D) Late log phase
E) Decline phase

Question 5

In a rapidly multiplying bacterial population, cell numbers increase

A) arithmetically.
B) logarithmically.
C) linearly.
D) indirectly.
E) additionally.

Question 6

Bacteria may be stored for several months

A) on a slant in the refrigerator, frozen in agar AND in broth at 37°C.
B) in broth at 37°C, on a slant in the refrigerator AND frozen in glycerol solution.
C) on a slant in the refrigerator, frozen in glycerol solution, AND freeze-dried.
D) freeze-dried, in broth at 37°C AND frozen in agar.
E) freeze-dried, frozen in glycerol solution AND in broth at 37°C.

Question 7

The solidifying agent used most successfully in bacterial nutrient media is

A) gelatin.
B) peptone.
C) agar.
D) starch.
E) agarose.

Question 8

In the growth curve of a bacteria population, the bacteria are rapidly increasing in number in the

A) lag phase.
B) exponential (log) phase.
C) stationary phase.
D) decline phase.
E) death phase.

Question 9

A urine sample with more than 100,000 organisms is considered indicative of infection. A urine sample containing 5,000 bacteria, with a generation time of 30 minutes, sits for 3 hours before finally being assayed. How many bacteria will then be present within the sample?

A) 320,000
B) 100,000
C) 64,000
D) 15,000
E) 10,000

Question 10

When doing experiments with bacteria,

A) it is usually not necessary to standardize which stage of growth is used.
B) it is best to use colonies, as all the bacteria in a colony are at the same stage of growth.
C) it is best to use bacteria from the same stage of growth.
D) the age of the bacteria is not important.
E) it is best to use mixed populations and biofilms.

Question 11

Generally the proteins of thermophiles

A) resist denaturation.
B) react more efficiently with DNA.
C) are easily denatured.
D) have very few amino acids.
E) are larger than those of mesophiles.

Question 12

During which phase of the bacterial growth curve does the total number of viable (live) cells decline?

A) Stationary
B) Lag
C) Exponential
D) Death
E) Infection

Question 13

The simplest technique for isolating bacteria in growth media is referred to as the

A) streak-plate method.
B) pour-plate method.
C) serial dilution method.
D) MPN method.
E) bacterial growth method.

Question 14

Late log phase of the bacterial growth curve

A) is characterized by the production of primary metabolites.
B) is characterized by the production of secondary metabolites.
C) is a transition into the death phase.
D) shows a decline in cell numbers.
E) is characterized by germination of endospores.

Question 15

Which of the statements about biofilms is True? 

A) Biofilms are very rarely involved in human bacterial infections.
B) Biofilms may protect organisms against harmful chemicals.
C) Biofilms are a peptidoglycan-encased community of microorganisms.
D) Biofilms may significantly inhibit bioremediation efforts.
E) Biofilms are very seldom found in a natural environment.

Question 16

During which phase of growth are bacteria most susceptible to antibiotics?

A) Lag
B) Stationary
C) Exponential (log)
D) Decline
E) Infection

Question 17

Prokaryotic cells divide by a process known as

A) conjugation.
B) mitosis.
C) binary fusion.
D) binary fission.
E) meiosis.

Question 18

The scientist that contributed most to the development of pure culture techniques was

A) Alexander Fleming.
B) Louis Pasteur.
C) Edward Jenner.
D) Robert Koch.
E) Paul Ehrlich.

Question 19

A hot tub (with a water temperature of 104°F or 40°C) would most likely contain

A) psychrophiles.
B) freezophiles.
C) mesophiles.
D) thermophiles.
E) hyperthermophiles.

Question 20

All the bacterial cells that result from the replication of a single original bacterial organism are referred to as a

A) mixed population.
B) pure culture.
C) lag culture.
D) mutant culture.
E) single culture.

Question 21

High concentrations of salt and sugar in foods

A) are useful in preserving the food AND tend to force water into a cell, causing plasmolysis.
B) have no effect on water availability AND are useful in preserving the food.
C) are useful in preserving the food AND tend to draw water out of a cell.
D) are useful in preserving the food AND force bacteria to divide
E) tend to force water into a cell, causing plasmolysis AND force bacteria to divide

Question 22

Trace elements

A) include zinc, copper, and manganese AND may be needed for enzyme function.
B) include zinc, copper, and manganese AND are required in large amounts.
C) may be needed for enzyme function AND are involved in maintaining pH in the cell.
D) are required in large amounts AND may be needed for enzyme function.
E) are involved in maintaining pH in the cell AND include zinc, copper, and manganese.

Question 23

Carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur may be considered

A) minor elements.
B) major elements.
C) neutral elements.
D) acidic elements.
E) trace elements.

Question 24

The optimum pH for growth of most species of bacteria is ________.

A) pH 5
B) pH 7
C) pH 9
D) pH 6
E) pH 1

Question 25

What would True about an organism called Bacillus fastidiosus?

A) It might be expected to be very flexible in its growth requirements.
B) It might be expected to be very strict in its growth requirements.
C) It could probably be grown on a minimal medium.
D) It might be expected to have a spherical shape.
E) It might be expected to depend on sunlight for energy.

Question 26

Organisms that are indifferent to the presence of oxygen and do not use it are

A) aerotolerant anaerobes.
B) facultative anaerobes.
C) obligate aerobes.
D) microaerophiles.
E) obligate anaerobes.

Question 27

Small organic molecules that must be provided to bacteria in order for them to grow are called

A) minerals.
B) growth factors.
C) water.
D) vitamins.
E) ions.

Question 28

The enzymes that deal with toxic oxygen-containing molecules is/are

A) glycolase AND superoxide dismutase.
B) superoxide dismutase AND cytochrome oxidase.
C) superoxide dismutase AND catalase.
D) catalase AND cytochrome oxidase.
E) cytochrome oxidase AND glycolase.

Question 29

Organisms that use CO₂ as their source of carbon are called

A) organotrophs.
B) heterotrophs.
C) autotrophs.
D) chemotrophs.
E) carbonotrophs.

Question 30

Organisms that require gaseous oxygen for metabolism are referred to as

A) facultative aerobes.
B) obligate aerobes.
C) facultative anaerobes.
D) microaerobes.
E) obligate anaerobes.

Question 31

Chemoheterotrophs

A) use sunlight as an energy source.
B) use preformed organic molecules as a carbon source.
C) use preformed organic molecules as an energy source.
D) use inorganic chemicals as an energy source.
E) use preformed organic molecules as a carbon source AND as an energy source.

Question 32

Mycobacterium leprae is typically found infecting the ears, toes, and fingers of its host due to its

A) requirement for well-oxygenated blood.
B) easy access to those body parts.
C) need for cooler temperatures.
D) long incubation period.
E) environmental distribution.

Question 33

Bacteria on fish caught in the Arctic Ocean would

A) be freezophiles AND continue to grow while the fish is in the refrigerator.
B) be mesophiles AND would continue to grow while the fish is in the refrigerator.
C) be mesophiles AND would not grow very well in the refrigerator.
D) be psychrophiles AND would continue to grow while the fish is in the refrigerator.
E) be thermophiles AND would not grow very well in the refrigerator.

Question 34

The prefix photo- indicates that an organism will make use of ________ for energy purposes.

A) chemicals
B) organics
C) light
D) inorganics
E) water

Question 35

Organisms may derive energy from

A) sunlight AND temperature gradients.
B) sunlight AND metabolizing chemical compounds.
C) metabolizing chemical compounds AND temperature gradients.
D) temperature gradients AND pH gradients.
E) sunlight AND pH gradients.

Question 36

The optimal temperature for most human pathogens might be expected to range from

A) 20-45°C.
B) 35-40°C.
C) 15-25°C.
D) 93-98.6°C.
E) 35-40°F

Question 37

Peptone

A) refers to a hydrolysate of carbohydrates used in growth media.
B) refers to a hydrolysate of proteins used in growth media.
C) consists of a water extract of beef.
D) consists of a mix of monosaccharides and oligosaccharides.
E) refers to a hydrolysate of proteins used in growth media AND consists of a water extract of beef.

Question 38

Which of the following is (are) obligate aerobes?

A) Clostridium botulinum
B) Escherichia coli
C) Micrococcus luteus
D) Helicobacter pylori
E) All of the answer choices are correct.

Question 39

Organisms that use organic molecules as their source of carbon are called

A) chemotrophs.
B) heterotrophs.
C) organoheterotrophs.
D) autotrophs.
E) organoautotrophs.

Question 40

Shake tubes are used to determine the

A) pH requirements for bacterial growth.
B) temperature requirements for bacterial growth.
C) oxygen requirements for bacterial growth.
D) salt requirements for bacterial growth.
E) nutrient requirements for bacterial growth.

Question 41

Products that limit pH changes are often incorporated into media and are referred to as

A) enzymes.
B) buffers.
C) bases.
D) acids.
E) neutrifiers.

Question 42

Medically important bacteria are often

A) grown on agar containing blood AND grown at 4°C.
B) grown at 37°C AND grown at a pH of 5.
C) grown on agar containing blood AND grown at 37°C.
D) grown on agar containing chocolate AND grown at 4°C.
E) grown at a pH of 5 AND grown at 4°C.

Question 43

MacConkey agar is

A) a selective medium.
B) a selective and differential medium.
C) a differential medium.
D) an enrichment medium.
E) an anaerobic medium.

Question 44

Agar

A) has chemical and physical properties that make it almost ideal for solidifying media.
B) is a useful nutrient source for most bacteria.
C) is a hydrolysate of carbohydrates and proteins.
D) stays liquid through the typical range of incubation temperatures.
E) only solidifies if it is cooled in a refrigerator for 48 hours.

Question 45

A microbe is discovered growing near a deep sea thermal vent. When researchers bring a sample up to the surface and try to grow it in a lab at room temperature in a normal incubator, they are unsuccessful. Why?

A) The pressure isn't the same at sea level as it is on the ocean floor and the microbe may require a very specific pressure.
B) Oxygen concentrations are very different between the two environments-it's possible the microbe is a strict anaerobe and is poisoned by the air (oxygen) in the lab.
C) Salt concentrations might be different in the media the researchers are attempting to use and the salt water the microbe is used to living in. This might be causing osmotic pressure differences that the microbe can't tolerate.
D) The temperature is probably different-the thermal vent would be very hot, while these researchers are trying to grow this microbe at room temperature. 
E) All of the answer choices are correct.

Question 46

You are working in a clinical laboratory in a hospital setting. You're handed a throat swab from a patient. You are told specifically that the physician is only interested in the presence and type of Gram positive cells. Identification isn't the main goal here-just a first step to work towards determining what Gram positive cells might be there. What might you do first to go about working towards this goal?

A) Perform a Gram stain.
B) Streak the sample for isolation on a tryptic soy agar general purpose medium plate.
C) Streak the sample for isolation on a medium that is selective for Gram positive cells.
D) Grow the microbes on the swab by inoculating a tryptic soy broth liquid medium tube.
E) Perform an acid-fast stain.

Question 47

In the cultivation of microaerophilic and anaerobic bacteria,

A) a(n) candle/anaerobe jar is sufficient.
B) atmospheric oxygen in a(n) candle/anaerobe jar is converted to water.
C) a packet containing chemicals that generate CO₂ and hydrogen is used in a(n) candle/anaerobic jar.
D) oxidizing agents are incorporated into the media that react with oxygen.
E) selective and differential media must always be used.

Question 48

Differential media only allow certain bacteria to grow.

Question 49

Prokaryotes are the only organisms able to use atmospheric nitrogen as a nitrogen source.

Question 50

You are a microbiologist working for a pharmaceutical company and discover a new secreted metabolite that can serve as a medication. Your company asks you to oversee the production of the metabolite. Which of the following does NOT need to be considered if you need to grow 5,000 liter cultures of bacteria for the purpose of harvesting the metabolite they secrete?

A) The death rate of the bacteria after stationary phase is complete.
B) The ideal rate of input of new nutrients into the culture to maintain the cells in log phase.
C) The ideal rate of pulling off some of the culture in order to maintain the cells in log phase.
D) The best way to mix the large vat in order to keep nutrient levels, temperature, and oxygen levels constant.
E) The best way to keep the pH of the entire mixture at the ideal level to promote log phase growth.

Question 51

Freezing is an effective means of destroying bacteria.

Question 52

One would expect most strict anaerobic organisms to have superoxide dismutase.

Question 53

It is assumed that every colony observed on a streak plate arose from a single bacterium.

Question 54

There are five stages of growth in an open system of culture.

Question 55

A medium that inhibits the growth of organisms other than the one being sought is called a(n)

A) synthetic medium.
B) specific culture medium.
C) selective medium.
D) enrichment medium.
E) differential medium.

Question 56

In microbiology, growth usually refers to an increase in size of the bacteria.

Question 57

Secondary metabolites may be antibiotics.

Question 58

Agar replaced gelatin as the gelling (solidifying) agent for media because

A) agar provides nutrients for rapid bacterial growth.
B) fewer bacteria can break down agar compared with gelatin.
C) agar is solid at temperatures as high as 90°C.
D) agar provides a pH range from 4-11.
E) agar is much easier to obtain than gelatin.

Question 59

A single bacterial cell may multiply to form a visible colony.

Question 60

Candle jars are usually used to

A) prevent candles from melting.
B) provide an atmosphere with CO₂.
C) stimulate the growth of obligate anaerobes.
D) prevent the growth of obligate aerobes.
E) enhance the growth of microaerophiles.

Question 61

The colonies of interest in this case are the blue-green presumptive Shigella colonies. However, growth on hektoen enteric agar is not sufficient for definitive identification. Further tests are needed. First, the lab technicians need to prepare larger numbers of Shigella from your patient's stool sample, and then they need to ensure that they are culturing a single species. The methods used to do this are ________, followed by ________. 

A) streak plating; pour plates
B) enrichment culture; Gram staining
C) Gram staining; enrichment culture
D) Gram staining; capsule staining
E) enrichment culture; streak plating

Question 62

Thayer-Martin agar typically contains a combination of antibiotics: vancomycin, colistin, nystatin, and trimethoprim. Please select the True statement.

A) The antibiotics in Thayer-Martin agar do not kill Gram-negative cells.
B) The antibiotics in the Thayer-Martin medium lyse the sheep RBCs.
C) Neisseria gonorrhoeae is not sensitive to the included antibiotics.
D) Fastidious bacteria are never impacted by common antibiotics.
E) Sheep blood cell in a growth medium protects bacteria from the impact of antibiotics.

Question 63

A halophilic, aerobic mesophile has a generation time of 20 minutes. You place 1 × 10⁴ of these organisms on an appropriate solid medium, and incubate the plate for 100 minutes. Select the False statement.

A) The growth medium contains NaCl.
B) The organism will grow at 40ᵒC. 
C) After incubation, a colony on the plate contains 3.2 × 10⁵ cells.
D) After incubation, a colony on the plate contains 5 × 10⁴ cells.
E) The organism produces superoxide dismutase and catalase.

Question 64

The lab technicians culture the sample on Thayer-Martin agar. This complex medium contains 5% sheep blood and a combination of antibiotics. This medium is 

A) differential.
B) selective AND differential.
C) selective.
D) aerobic.
E) chemically defined.

Question 65

You are determining the number of colony forming units (CFUs) for Susan, who has a urinary tract infection (UTI). You added 1 mL of Susan's urine sample to 99 mL of diluent, and spread 0.1 mL of that dilution on a culture medium. After appropriate incubation, you count 143 colonies on the plate. What was the concentration of bacteria in the original urine sample? 

A) 1.43 cells/ mL
B) 1.43 × 10² cells/ mL
C) 1.43 × 10³ cells/ mL
D) 1.43 × 10⁵ cells/ mL
E) Cannot be determined

Question 66

In addition to the few Shigella colonies that are noted, there are also abundant salmon pink colonies, around which the medium has turned yellow, losing its original blue color. You know that hektoen enteric agar must contain ________. 

A) lactose
B) a pH indicator
C) a weak acid
D) malachite green
E) penicillin

Question 67

A physician sends a stool sample to your lab, and wants to know if there are lactose fermenting microbes in the sample. How might you determine if these microbes are present or not from this mixed-microbe specimen?

A) Streak the sample for isolation on Thayer-Martin agar (which contains lactose and particular antibiotics for selectivity).
B) Streak the sample for isolation on a blood agar plate (which contains lactose and red blood cells that enrich the culture for iron).
C) Streak the sample for isolation on a MacConkey agar plate (which contains lactose and a pH indicator that turns pink when acid byproducts are present).
D) Either Thayer-Martin agar or blood agar would work, as long as the plates are incubated in an anaerobic chamber.  
E) None of the answer choices would work-there's no way to reliably determine this feature from the specimen given.

Question 68

Diagnosis of legionellosis depends partly on culture of the causative agent from medical samples. Typically, the organism is grown on buffered charcoal yeast extract (BCYE) agar. What essential component must this medium have to ensure growth of L. pneumophila?

A) red blood cells
B) chlorine
C) NaCl
D) cysteine
E) All of the answer choices are correct.

Question 69

Clostridium paradoxum grows optimally at 55°C, pH 9.3; it will not grow in the presence of O₂. Please select the True statement about this organism.

A) It is spherical in shape.
B) It is a psychrophile.
C) It is an obligate anaerobe.
D) It is an acidophile.
E) It is an aerotolerant anaerobe.

Question 70

If you are asked to make 200 mL of Thayer-Martin agar, who much sheep's blood would you add to the medium? Recall that this complex medium contains 5% sheep blood.

A) 10%
B) 5 mL
C) 10 mL
D) Random quantities
E) 10,000 RBCs

Question 71

You are in charge of water quality for your city's water treatment plant. Of the methods at your disposal, which will be the most efficient and cheapest method of determining the number of viable bacteria in the water coming out of your plant?

A) Direct counts using a microscope and a counting chamber.
B) Using a Coulter counter machine.
C) Performing serial dilutions and doing spread plate counts.
D) Using membrane filtration followed by placing the membrane in a growth medium for colony counts after incubation.
E) Biochemical analysis of secondary metabolites in the water that are given off by bacteria.

Question 72

Shigella species and Salmonella species are classified as facultative anaerobes. You know that given this information, the bacteria in your patient's fecal culture will grow best

A) in the absence of oxygen.
B) in the presence of oxygen.
C) at low levels of oxygen.
D) in high levels of carbon dioxide.
E) if catalase is added to the medium.

Question 73

Eosin methylene blue agar (EMB) is a selective and differential medium. The dyes in the medium inhibit most Gram-positive organisms. Gram-negative organisms such as the coliforms grow on this medium. Coliforms that are fecal in origin produce colonies with a metallic green color on EMB, while those that are non-fecal produce colorless colonies. You plate a urine sample onto an EMB plate and incubate it. Metallic green colonies develop. From this, you can conclude that 

A) the sample contains bacteria that are Gram-negative AND are non-fecal in origin.
B) the sample contains bacteria that are Gram-negative AND are fecal in origin.
C) the sample contains bacteria that are Gram-positive AND are fecal in origin.
D) the bacteria in the colonies are Gram-positive AND are rod-shaped.
E) normal microbiota in the bladder is fecal in origin AND is aerobic.

Question 74

You take a stool sample from Mrs. Thomas, and send it to the lab for analysis. You tell her that the technicians will do a variety of tests to confirm the identity of the organism causing her illness. The first thing that will be done is to inoculate some of her stool sample onto a medium called hektoen enteric (HE) agar. On this medium, Shigella species produce blue-green colonies, while Salmonella produces blue-green colonies with a black center, and most Gram-positive bacteria do not grow at all. You explain to Mrs. Thomas that this type of medium is called a(n) ________ medium.

A) selective
B) differential
C) enrichment
D) selective and differential
E) differential and enrichment

Question 75

You are culturing a new bacterium in the laboratory. You cannot find any glucose it the lab when you are making growth medium, so you decide to use honey instead. You add twice as much honey than is called for in the medium recipe, because you want to give the organism the best opportunity or growth. To your surprise, the organism does not grow on your modified medium. Select the most likely explanation.

A) The growth medium became hypotonic with the addition of so much honey; the bacteria underwent plasmolysis and died.
B) The growth medium became hypertonic with the addition of so much honey; the bacteria underwent plasmolysis and died.
C) The growth medium became halophilic with the addition of so much honey; the bacteria underwent plasmolysis and died.
D) The growth medium became hypertonic with the addition of so much honey; the bacteria underwent osmotic lysis and died.
E) The growth medium became hypotonic with the addition of so much honey; the bacteria underwent simple diffusion and burst.

Question 76

L. pneumophila is widespread and is found in various water sources, including hot tubs, water cooling towers, swimming pools, grocery store misters, and shower water. Select the False statement  regarding the organism, given this information.

A) It survives in the presence of chlorine.
B) It is a mesophile.
C) It is an obligate anaerobe.
D) It can survive in water pipes.
E) It is a mesophile AND it can survive the presence of chlorine.

Question 77

You take absorbance readings on a spectrophotometer across a 6-hour culture of E. coli cells growing in tryptic soy broth (TSB). Your absorbance readings clearly indicate a lag phase, a log phase, and a stationary phase. You come back in and take readings at 8, 10, 12, 14, and 16 hours, but the absorbance number remains the same. Shouldn't it start coming down as the closed batch culture enters death phase? What's the most likely thing that is happening?

A) Something is likely wrong with the spectrophotometer and it isn't measuring the correct values. Perhaps something is on the detector, making it register Falsely high absorbance numbers.
B) A spectrophotometer can measure absorbance as an indicator of cell number, but can't discriminate between a live cell and a dead one. The presence of dead cells keeps the absorbance high even into the death phase.
C) E. coli just grows slowly, and has a long generation time. After 16 hours the cells are still in stationary phase, so the cell numbers are expectedly constant. 
D) Perhaps there's a big smudge of something on the tube that is blocking some of the light. This would lead to an elevated reading for every timepoint after the smudge was placed on the tube.
E) There is no point in measuring the absorbance of the culture because the cells are bacterial. It would make more sense to measure would the transmission value.

Question 78

In some labs, samples containing suspected L. pneumophila are cultured on traditional BCYE medium as well as BCYE medium lacking L-cysteine. How would L. pneumohila be identified in this situation?

A) Compare the two plates. Colonies that grow on traditional BYCE medium but not on BYCE medium lacking cysteine are likely L. pneumophila.
B) Compare the two plates. Colonies that grow on BYCE medium lacking cysteine but not on traditional BYCE medium are likely L. pneumophila.
C) Compare the two plates. Colonies that grow on both traditional BYCE medium and on BYCE medium lacking cysteine are likely L. pneumophila.
D) Compare the two plates. Colonies that do not grow on traditional BYCE medium or on BYCE medium lacking cysteine, but do grow on nutrient agar are likely L. pneumophila.
E) Compare the two plates. Colonies that grow on traditional BYCE medium and are blue, yellow or cyan in color are likely L. pneumophila.

Question 79

The causative organism of gonorrhea is Neisseria gonorrhoeae, a fastidious, Gram-negative diplococcus. What does fastidious mean in this context?

A) An organism with complex nutritional requirements.
B) An organism that requires oxygen for growth.
C) An organism that survives in the presence of specific antibiotics.
D) An organism that only grows in pure culture.
E) An organism that requires a living host.

Question 80

On HE medium, Shigella species produce blue-green colonies, while Salmonella produces blue-green colonies with a black center. There are two noticeable types of colonies growing on the hektoen enteric (HE) medium in Mrs. Thomas' test. One type of colony is greenish in color. This leads you to conclude that the bacteria in these colonies 

A) is Gram-negative and is likely Shigella.
B) is Gram-negative and is likely Salmonella.
C)  is Gram-positive and is likely Shigella.
D) is Gram-positive and is likely Salmonella.
E) is Gram-neutral and is likely Salmonella.