30 terms

lab quiz 2

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What is the definition of selective media?
Selective media incorporate chemical substances that inhibit the growth of one type of bacteria while permitting the growth of another.
What is the definition of differential media?
Differential media incorporate chemical compounds that produce characteristic changes in the appearance of the bacterial colonies.
What is the definition of enriched media?
Enriched media have been supplemented with highly nutritious materials for the purpose of cultivating fastidious organisms.
Which of the following associations is INCORRECT regarding selective media?
*Crystal violet agar: inhibits the growth of gram-negative organisms, used to isolate gram-positive organisms
* Crystal violet agar: inhibits the growth of gram-positive organisms, used to isolate gram-negative organisms
* Phenylethyl alcohol agar: inhibits the growth of gram-negative organisms, used to isolate gram-positive organisms
* NaCl (sodium chloride) agar: inhibits the growth of a non-halophilic organisms, often used to isolate Staphylococcus
Crystal violet agar: inhibits the growth of gram-negative organisms, used to isolate gram-positive organisms
What is the purpose of adding phenol red to mannitol salt agar?
Phenol red permits the differentiation of bacteria based on their ability to ferment mannitol.
What is the purpose of adding eosin and methylene blue to eosin-methylene blue agar?
Eosin and methylene blue are dyes that precipitate on the surface of acid-producing colonies of enteric lactose fermenters, creating a metallic green sheen.
Which of the following is the most accurate description of the appearance of Staphylococcus aureus growing on mannitol salt agar?
white to cream colored colonies surrounded by yellow halos in the agar
In the streak plate technique, the intent is to isolate bacteria by dilution in theory by _________________.
dilution on a solid surface
Which of the following does NOT describe a colony?
*an outcome on a successful streak plate
*one kind of bacterium
*used to develop a pure culture
*a visible growth on a streak plate
*a mixture of microbes in an environment
a mixture of microbes in an environment
Which of the following media would be useful for isolating bacteria that are in small number in a mixed culture?
selective media
Selective media can be useful in isolating bacteria.Mannitol salt agar is selective because of its _____________.
salt content
Dyes such as phenol red or methylene blue are used in culture media to _________________.
detect pH changes due to metabolism
The reason that Staphylococcus aureus turns yellow on MSA is ___________.
the microbes have fermented mannitol
MacConkey (MAC) agar is selective because of __________________.
bile salts and crystal violet
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 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
Endospores are destroyed by which of these methods?
Autoclaving.
Which one of the following methods of control involves the hottest temperature?
Autoclaving
A bactericidal chemical kills bacteria.
true
Imagine that you incubate bacteria in nutrient broth containing an antimicrobial chemical. Upon observing no growth after 48 hours, you make a subculture in a tube of nutrient broth that does not contain the antimicrobial chemical. If the bacteria grow in the subculture, you can conclude that the chemical ____________________.
is bacteriostatic
The MIC is the _______________________.
lowest concentration of a substance that prevents bacterial growth
When a physician sends a clinical sample to the lab and asks for antibiotic susceptibility to be determined, the lab technician determines the susceptibility by _____________________.
performing the Kirby-Bauer test
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 be seen as evidence of synergism in the disk-diffusion method?
enhanced zones of inhibition in the area between two adjacent disks
Kirby Bauer susceptibility test results are reported as S, I, or R. Broth dilution susceptibility tests are reported as MICs. Which statement about these tests is correct?
Kirby Bauer tests provide qualitative results while broth dilution tests provide quantitative results.
How does UV radiation damage microorganisms
The DNA is damaged by the formation of thymine dimers
What skin quality(s) protects microbes from removal by handwashing?
Oil and layers of cells
Which of the following provides quantitative data regarding the antibiotic susceptibility of a particular bacteria?
broth dilution test