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Why do we use the term colony-forming units, instead of cells, when expressing concentration of bacteria in a sample?
· Sometimes a group of cells form a single colony
· Weight 1 g of sample and place into 9 mL of sterile water
· Prepare serial dilution of the sample
· Deliver inoculum to each plate
· Pour melted agar into plates
· Stack plates, invert, and incubate
· Count colonies and calculate concentration
· Gas and acid produced from lactose fermentation
You observe a microbial colony on a glycerol yeast agar. This microbe is likely to be
Which of the following is NOT a characteristic of the coliforms?
They are coccus shape
· They DO
o Able to ferment lactose
o Present in human feces
o Don’t form endospores
o Are gram-negative
The most probable number method is used to determine the number of speies of coliforms in a sample
In the most probably number test, various amounts of the sample are added to
· Lactose broth tubes
Which of these is involved in the presumptive test portion of a multiple-tube technique?
· Determining whether gas was produced
To determine whether ammonia is produced from peptones (proteins), _____ is added to the sample and will change color if ammonia is present
Ammonia test reagent
The deamination of which of these substances in the soil produces ammonia?
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?
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 microorganisms is susceptible to an antibiotic?
· The diameter of the zone of inhibition surrounding the antibiotic disks
What is the 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
· What is important
o The thickness of the agar
o The size of the antibiotic disk
o The number of bacteria plated
Why is it critical to use aseptic technique when transferring the antibiotic disks to the agar ?
· Contaminating organisms could produce their own antibiotics
· Contaminating microorganisms could break down the antibiotics
· Contaminating microorganisms could alter the diffusion of the antibiotics thorugh the agar
What are the three possible outcomes for each antibiotic: microorganism pair in a Kirby-Bauer assay?
· Susceptible, resistant, or intermediate
Blood agar is used in the Kirby-Bauer disk-diffusion test because it allows for easy diffusion of the antimicrobial agent through the agar
The disk-diffusion method determines which antibiotics are resistant to the bacteria
The effectiveness of two antibiotics administered together may be greater than the effectiveness if either antibiotic were used alone. This is known as synergism. What would have been seen as evidence of synergism in the disk-diffusion method?
· Enhanced zones of inhibition in the area between two adjacent disks
In the disk-diffusion method, why is the zone of inhibition circular?
· Diffusion occurs equally from the edge of the disk
Which of the following is NOT a mechanism by which antibiotics control microbial growth?
Causing mutations in DNA
· They can by
o Destroying the cell membrane
o Inhibiting nucleic acid synthesis
o Inhibiting protein synthesis
The origins of all antibiotics are living microorganisms.
Sensitivity to an antimicrobial agent generally corresponds to small zones of inhibition.
Which of the following could be a realistic representation of a zone of inhibition?
A broad-spectrum antibiotic would likely affect ____
· gram-positive and gram-negative bacteria
The size of the zone of inhibition must be compared to the performance standards for that antimicrobial agent to determine susceptibility or resistance.
Which of the following best describes transformation?
· Transfer of genetic material from the environment into a bacterium
How does DNA get into the environment for transformation to occur?
· It is released when a bacterium dies
How could transformation be beneficial to microorganisms?
· Transformation allows microorgansims to develop new characteristics or abilities
· Transformation allows microorganisms to acquire new genes
· Transformation could allow the organisms to become pathogenic
In the experiment described in your lab manual, the transformation is ___
Which of the following terms describes the organisms that has been transformed?
· None of the available answers (autotroph, prototroph, auxotroph) describe an organism that has been transformed.
Which of the following can be used to transform the bacteria?
· Both genomic and plasmid DNA
In the experiment described in this lab, how can you tell if the organisms have been transformed?
· You can determine if it acquired the appropriate new abilities or characteristics
Which of the following, if found in the environment, could lead to transformation of a competent bacterium?
The purpose of UV light in this experiment is to detect transformed cells
What method is used in this experiment to make the plasma membrane of E. coli more fluid and easier for the foreign DNA to enter?
· Heat shocking
The purpose of Ca2+ in this experiment is to _____
· Neutralize phosphates in DNA and the plasma membrane
· A plasmid containing gfp and ampicillin-resistance genes
LB agar is _____
· Nutritionally complete
Transformation is the acquisition of DNA
· From solution
A cell that can take up foreign DNA is referred to as
E. Coli naturally fluoresce
In this experiment, E. coli cells that acquire pGLO will ________
· Grow in the presence of amphicillin
How do you know if your transformation was successful?
· Colonies will display novel characteristics not found in the wild type
How can you ensrue that the organisms that grew on your experimental plates were not contaminated?
· Any contaminating colonies will not display the phenotypic characteristics attributed to the genetic material you used for transformation
· Spontaneous mutations do not occur unless there is a mutagen present. This agar did not contain mutagensActual refutes
- It is very unlikely that spontaneous mutation events would lead to the same mutation in a variety of organisms
- It is not possible that a spontaneous mutation in just one generation would lead to the acquisition of an entire gene- Spontaneous mutation is much too rare for hundreds of colonies to display this new characteristic
What would you expect ot happen if you tried to transform a competent microorganism with two different types of plasmids
· The organism would express genes from both of the plasmids
Correctly identify the steps and elements in this bacteriophage plaque assay
· Mixture of molten agar, bacteria, and diluted phage suspension
· Cell-phage mixture is poured onto an agar plate
· Mixture is left to solidify
· Incubation allows microbial growth and phage replication
· Phage plaques
· Lawn of host cells
Bacteriophages are indicated by areas called _____ when grown in a solid medium containing host cells.
Viruses must be grown in susceptible host cells
The number of visible plaques counted equals the number of phage particles in the original stock culture
_____ are viruses that infect bacteria
A 21 plaques are recorded on an agar plate, you should use that number to calculate the overall phage count.
Phage typing can be used to identify bacteria because _____
· Phages infect specific bacteria
In theory, each plaque on a plate corresponds to -____
· One infective virus in the initial suspension
· The largest problem is that single viruses may create multiple plaques, resulting in overestimates of the number of viruses present (FALSE)What is true?
o The plaques must be at a density that can be counted on the plate: high and low densirites may resulti n inaccurate counts.
o The plaques must be clearly visible in order to be counted accurately; this technique cannot be used with viruses that do not cause cellular damage
o The largest problem is that the count may underestimate the total number of viral particles, as not all virions may be able to cause infection
When determining the number of bacterial virus particles in a suspension, why is the number obtained always less than the actual viral titer?
· Because all of the virus particles do not infect with 100% efficiency
Viruses infecting ____ are typically the easiest to grow in the laboratory
The concentration of infection plaque forming units (pfu) per volume of fluid is known as the
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