Deck 6: Bacterial Growth, Nutrition, and Differentiation

Question 1

Which of the following occurs when a microorganism is found in an environment below its minimum growth temperature?

A) The cell dies.
B) Growth stops because the cell membrane melts.
C) Growth stops because enzymatic processes become sluggish.
D) Growth slows but does not stop.

Answer 1

C

Question 2

What advantage does the plating method shown on the left panel below have over the plating method shown in the right panel?

A) It can be used to isolate pure colonies.
B) It can be used to culture viable organisms.
C) It can be used to produce confluent growth.
D) It can be used to quantify the number of organisms in a given bacterial sample.

Answer 2

D

Question 3

Which of the following is NOT a problem with the viable count method of cell quantification?

A) underestimation of the number of living cells in the culture
B) takes too long if you want to immediately study cells at a particular growth phase
C) not accurate for organisms whose cells remain attached (for example, Streptococci growing in chains)
D) not useful for living cells

Answer 3

D

Question 4

Which of the following is NOT happening during the lag phase of growth?

A) Cells are at their largest.
B) Genes for growth in the specific environment are turned on.
C) Cell components are being synthesized.
D) Cells are detecting their environment.

Question 5

What classification is also given to barophilic organisms that grow at the ocean floor?

A) mesophilic
B) psychrophilic
C) halophilic
D) acidophilic

Question 6

Which of the following is NOT required for microorganisms to grow and divide?

A) DNA replication
B) binary fission
C) equatorial septum formation
D) conjugation

Question 7

What is the correct term for the chemical conversion shown below?
N₂ →NH₄⁺

A) phototrophy
B) nitrification
C) denitrification
D) nitrogen fixation

Question 8

Bacteria begin to participate in quorum sensing at which stage of growth?

A) late log phase
B) log phase
C) stationary phase
D) death phase

Question 9

A new enzyme that helps protect a bacterial cell from reactive oxygen species has been discovered.During which phase of growth would you expect the gene that codes for this enzyme to be expressed?

A) lag phase
B) log phase
C) late log phase
D) stationary phase

Question 10

Which of the following statements regarding examples of chemotrophy is FALSE?

A) Glucose is an oxidized compound that freely donates electrons to NAD, a more reduced compound.
B) Glucose is a reduced compound that freely donates electrons to NAD, a more oxidized compound.
C) NAD plays an important role in chemotrophic metabolism.
D) Glucose is an important chemotrophic carbon source.

Question 11

Which of the following could describe the relationship between the cyanobacterium Nostoc and E.coli related to the carbon cycle?

A) Nostoc produces carbohydrates from lithotrophy, and E. coli breaks down the carbohydrates to generate CO₂.
B) Nostoc produces carbohydrates from phototrophy, and E. coli breaks down the carbohydrates to generate CO₂.
C) Nostoc produces CO₂ that E. coli turns into carbohydrates.
D) E. coli produces carbohydrates that Nostoc uses as energy to produce more carbohydrates.

Question 12

Examine the media recipes shown.What ingredients make Luria Bertani a complex medium as opposed to a chemically defined minimal medium?

A) tryptone and NaCl
B) tryptone and yeast extract
C) NaCl and yeast extract
D) Luria Bertani is a chemically defined minimal medium.

Question 13

Mannitol salts agar is a medium that contains a high concentration of salt (7.5%)and mannitol as a fermentable carbon source.Few organisms are able to grow on it because of its high salt concentration.Organisms that can grow and ferment mannitol will produce an acid that interacts with the pH indicator in the media,turning it yellow.Nonmannitol-fermenting organisms grow without any change to the media.Which of the following correctly describes this medium?

A) selective
B) differential
C) selective and differential
D) neither

Question 14

Which of the following can be used to directly count bacterial cells without the use of a microscope?

A) viable counts
B) optical density
C) fluorescence-activated cell sorter
D) Petroff-Hauser counting chamber

Question 15

Fastidious organisms would be best grown on which type of media?

A) enriched
B) synthetic
C) minimal
D) selective

Question 16

A culture of Salmonella increases from 20 cells to over 10,000 cells in just three hours.Of what is this an example?

A) lag phase
B) doubling time
C) budding
D) exponential growth

Question 17

Given the incredibly fast division times of bacterial cells,which of the following could explain why we are NOT surrounded by large mountains of bacterial cells?

A) Bacteria produce too much toxic iron.
B) Bacteria require a host cell to grow.
C) Bacteria are outcompeted by viruses.
D) Bacteria run out of nitrogen.

Question 18

Which of the following is needed as an important enzyme cofactor for microbial growth?

A) Na+
B) Mg²+
C) sulfur
D) oxygen

Question 19

Which of the following can be most efficiently used to measure bacterial growth in real time?

A) FACS
B) spectrophotometer
C) Petroff-Hauser counting chamber
D) fluorescent microscope

Question 20

If you start with 14 organisms at time 0,how many organisms will you have after 9 generations,assuming exponential growth?

A) 126
B) 512
C) 7,168
D) 14,336

Question 21

Why might a facultative organism prefer aerobic respiration over fermentation when carbohydrates become scarce?

A) Facultative organisms never prefer aerobic respiration to fermentation.
B) It gets more energy from fermentation.
C) It gets more energy from aerobic respiration.
D) It gets less energy from aerobic respiration.

Question 22

What is the purpose of the palladium packet in the anaerobic jar?

A) to catalyze a reaction between H₂ and residual O₂ in the jar to remove all the O₂
B) to remove CO₂ that can be converted to O₂
C) to provide O₂ for aerobic respiration
D) to provide N₂ for protein synthesis

Question 23

Which of the following cellular components could be found in high concentrations in a halophilic microorganism?

A) Na+/ K+ ion pump
B) citric acid
C) cold-tolerant enzymes
D) asuperoxide dismutase

Question 24

Production of urease by Helicobacter pylori allows it to do which of the following?

A) sense when it has entered the intracellular environment of its host
B) survive in basic conditions
C) increase production of ion pumps
D) neutralize stomach pH to survive in acidic conditions

Question 25

Which of the following is NOT necessary for endospore formation?

A) exopolysaccharide formation
B) peptidoglycan synthesis
C) dipicolinic acid synthesis
D) calcium transport

Question 26

Aerobic bacteria are capable of using ________ as a terminal electron acceptor in the electron transport chain.

Question 27

CASE HISTORY
A young mother who recently emigrated from Uganda brought her sick 18-month-old infant,Mirembe,to a New York City emergency room.The infant was crying uncontrollably,especially when the physician tried to move her head.Meningitis (an infection of the spinal fluid and membrane surrounding the brain)was suspected,and a spinal tap was performed to collect cerebrospinal fluid (CSF).The fluid,which appeared cloudy,was sent to the laboratory.
CSF should be free of microbes,but a microscopic examination revealed Gram-negative bacilli.The technician cultured the sample on various solid media.The organism failed to grow on blood agar plates containing intact red blood cells (RBCs)but did grow on a medium containing lysed RBCs (called chocolate agar because of its color).The organism recovered from the CSF also grew on a relatively simple medium containing growth factors known as X and V.
The diagnosis was meningitis caused by the bacterium Haemophilus influenzae.The child received antibiotics and made a full recovery.
The blood agar plates used to culture Mirembe's sample contain intact red blood cells and agar.Organisms that are capable of lysing the red blood cells may produce green-appearing zones of partial hemolysis or clear-appearing zones of complete hemolysis around colonies that are easily visually distinguishable.This medium is best described as:

A) selective.
B) differential.
C) chemically defined.
D) synthetic.

Question 28

Which of the following is NOT an example of a bacterial organism that can form a biofilm?

A) All bacterial organisms can form biofilms.
B) Pseudomonas aeruginosa
C) Escherichia coli
D) Bacillus anthracis

Question 29

Direct counting of bacterial cells under the microscope can be accomplished using a ________.

Question 30

If an error occurred during the sporulation process and small acid-soluble proteins were not included in the spore,what would be the effect?

A) The spore would only exist for 100 years.
B) The spore will be more likely to germinate.
C) The spore will be less resistant to heat.
D) The spore will be less resistant to ultraviolet light.

Question 31

Why do strict anaerobes die in the presence of oxygen?

A) They are vulnerable to reactive oxygen species.
B) They are not able to get enough energy without using oxygen as a terminal electron acceptor.
C) They do not use oxygen as a terminal electron acceptor.
D) Strict anaerobes do not die in the presence of oxygen.

Question 32

Most bacteria in nature grow at a very slow rate,a situation that can be mimicked using a ________.

Question 33

A ________ contains only the most basic compounds an organism needs to grow and nothing more.

Question 34

If you were trying to isolate a pure culture of Staphylococcus aureus from the skin lesion of an infected individual,you would use appropriate sampling techniques and would specifically have to culture the microorganism onto ________.

Question 35

Which of the following is true regarding an environment with a high osmolarity?

A) It has a low salt concentration.
B) It has a high pH.
C) It has a high water activity.
D) It has a low water activity.

Question 36

Consider the tube shown.What type of organism would grow only at the bottom of the tube?

A) microaerophile
B) aerotolerant anaerobe
C) strict anaerobe
D) strict aerobe

Question 37

Which of the following is NOT involved in biofilm formation or function?

A) rorespore engulfment
B) quorum sensing
C) exopolysaccharide formation
D) antibiotic resistance

Question 38

Why do bacterial organisms form a biofilm?

A) to claim territory and fight off competing organisms of a different species
B) to attach to a surface in an area where food is plentiful
C) to find a food source when nutrients are scarce
D) to mate with other bacterial organisms of the same or different species

Question 39

Which of the following is NOT a toxic by-product of oxygen metabolism?

A) superoxide
B) hydroxide radicals
C) hydrogen peroxide
D) dihydrogen oxide

Question 40

Mesophilic proteins are ________ flexible than psychrophilic proteins.

Question 41

List and describe two differences between anaerobic respiration and fermentation.

Question 42

Explain why extremophiles are not a pathogenic threat to humans.

Question 43

Explain what effect the loss of heterotrophs would have on the carbon cycle and the world.

Question 44

Explain metabolically why bacteria grow faster in complex media than in minimal media.

Question 45

Examine the figure on endospore formation shown.Explain what is happening at stage III and how it leads to the remarkable heat and chemical resistance of endospores.

Question 46

What is a batch culture? Describe how it can be used to illustrate the bacterial growth curve.

Question 47

Within aquatic environments,bacteria are mainly found associated with surfaces in the form of a ________.

Question 48

The production of ________ mechanisms in a biofilm helps maintain the viability of a biofilm during an infection.

Question 49

Explain how many microorganisms are able to grow at pH levels outside the functional pH range of their enzymes.

Question 50

How is it possible for a strict anaerobic bacteria to cause a disease in humans?

Question 51

CASE HISTORY
A fecal sample from a patient with diarrhea was streaked onto MacConkey lactose agar medium,a medium that selectively prevents the growth of Gram-positive bacteria but will differentiate Gram-negative bacteria that can ferment lactose from those that cannot.The next day,several different types of bacterial colonies were visible on the agar plate.Some were red;others were white.The white colonies led the clinical microbiologist to suspect that the patient was infected with the Gram-negative bacillus Salmonella enterica serovar typhimurium.
MacConkey lactose agar medium selectively prevents the growth of Gram-positive bacteria but will differentiate Gram-negative bacteria that can ferment lactose from those that cannot.The use of these types of media,called selective and differential media,are extremely helpful when microbiologists already have an idea of the pathogen present.What led the microbiologist to believe that the white colonies were Salmonella enterica serovar typhimurium?

Question 52

CASE HISTORY
Robert,a 21-year-old software salesman from Dallas,Texas,presented to the Parkland Hospital emergency room with three days of cramping pain in the midgastric and lower abdominal areas.He had no nausea,vomiting,or diarrhea.Upon examination,the patient screamed in severe pain when the clinician pressed on his lower right abdomen.Blood samples were obtained and sent for bacteriological culture.A blood culture bottle incubated in air appeared sterile,whereas another blood culture bottle placed in a special chamber that removed oxygen grew thick with bacteria.A subsequent exploratory laparoscopy,in which a small incision is used to perform surgery and minimize scarring,revealed a grossly inflamed appendix that released a liter of pus when removed.The diagnosis was appendicitis caused by the anaerobic bacterium Bacteroides fragilis-a common intestinal microbe.
How should the microbe causing Robert's infection be cultured? Will all of the microbes present in a sample taken from the site of his infection be able to grow in this culture? Explain your answer.

Question 53

List the three factors that complicate measuring bacterial growth in a human host.Describe how each one makes measuring bacterial growth difficult.