Micro Lab

What is an antibiotic? A) A synthetic chemical that kills bacteria B) An organism that inhibits the growth of other organisms C) A chemical that inhibits microbial growth D) All available answers are characteristics of an antibiotic.

A chemical that inhibits microbial growth

Why is it critical to use aseptic technique when transferring the antibiotic disks to the agar? A) Contaminating microorganisms could break down the antibiotics. B) Contaminating organisms could produce their own antibiotics. C) Contaminating microorganisms could alter the diffusion of the antibiotics through the agar. D) All available answers are correct.

All available answers are correct.

Which of the following associations is INCORRECT regarding selective media? A) Crystal violet agar: inhibits the growth of gram-positive organisms, used to isolate gram-negative organisms B) NaCl (sodium chloride) agar: inhibits the growth of a non-halophilic organisms, often used to isolate Staphylococcus C) Crystal violet agar: inhibits the growth of gram-negative organisms, used to isolate gram-positive organisms D) Phenylethyl alcohol agar: inhibits the growth of gram-negative organisms, used to isolate gram-positive organisms

Crystal violet agar: inhibits the growth of gram-negative organisms, used to isolate gram-positive organisms

What is the definition of differential media? A) Differential media incorporate chemical substances that inhibit the growth of one type of bacteria while permitting the growth of another. B) Differential media have a wide variety of fuel supplies available and support the growth of most types of bacteria. C) Differential media have been supplemented with highly nutritious materials for the purpose of cultivating fastidious organisms. D) Differential media incorporate chemical compounds that produce characteristic changes in the appearance of the bacterial colonies.

Differential media incorporate chemical compounds that produce characteristic changes in the appearance of the bacterial colonies.

What is the definition of enriched media? A) Enriched media have a wide variety of fuel supplies available and support the growth of most types of bacteria. B) Enriched media incorporate chemical compounds that produce characteristic changes in the appearance of the bacterial colonies. C) Enriched media incorporate chemical substances that inhibit the growth of one type of bacteria while permitting the growth of another. D) Enriched media have been supplemented with highly nutritious materials for the purpose of cultivating fastidious organisms.

Enriched media have been supplemented with highly nutritious materials for the purpose of cultivating fastidious organisms.

What is the purpose of adding eosin and methylene blue to eosin-methylene blue agar? A) Eosin and methylene blue are pH indicators that turn blue when lactose is fermented. B) Eosin and methylene blue are present to inhibit the growth of gram-negative organisms. C) Eosin and methylene blue are dyes that precipitate on the surface of acid-producing colonies of enteric lactose fermenters, creating a metallic green sheen. D) Eosin and methylene blue directly inhibit the growth of lactose nonfermenters.

Eosin and methylene blue are dyes that precipitate on the surface of acid-producing colonies of enteric lactose fermenters, creating a metallic green sheen.

Hemolytic bacteria can only grow on blood agar. A) True B) False

False

If a yellow halo is present around a colony on a mannitol salt plate, the bacterium cannot ferment mannitol. A) True B) False

False

On a mannitol salt plate, bacteria are using the salt (NaCl) for their energy source. A) True B) False

False

The coagulase test and catalase test are used to detect the presence of the same enzyme. A) True B) False

False

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

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

What is the purpose of adding phenol red to mannitol salt agar? A) Phenol red permits the differentiation of bacteria based on their ability to ferment mannitol. B) Phenol red permits the differentiation of bacteria based on their ability to withstand high salt concentrations. C) Phenol red permits the differentiation of bacteria based on their ability to ferment lactose. D) Phenol red inhibits the growth of gram-positive organisms.

Phenol red permits the differentiation of bacteria based on their ability to ferment mannitol.

What is the definition of selective media? A) Selective media have a wide variety of fuel supplies available and support the growth of most types of bacteria. B) Selective media incorporate chemical compounds that produce characteristic changes in the appearance of the bacterial colonies. C) Selective media incorporate chemical substances that inhibit the growth of one type of bacteria while permitting the growth of another. D) Selective media have been supplemented with highly nutritious materials for the purpose of cultivating fastidious organisms.

Selective media incorporate chemical substances that inhibit the growth of one type of bacteria while permitting the growth of another.

What are the three possible outcomes for each antibiotic: microorganism pair in a Kirby-Bauer assay? A) Stunted, robust, or intermediate B) Susceptible, resistant, or indeterminate C) Susceptible, resistant, or intermediate D) Similar, reversion, or indeterminate

Susceptible, resistant, or intermediate

Which of these would be useful in distinguishing whether an unknown culture is Staphylococcus aureus or S. epidermidis? A) Testing for presence of catalase. B) Testing for ability to grow on mannitol salt agar. C) Conducting a Gram stain. D) Testing for presence of coagulase.

Testing for presence of coagulase.

What is a zone of inhibition? A) The area around the Bunsen burner that is considered sterile B) The area around the antibiotic disk in which bacteria cannot grow C) The area between two antagonistic antibiotics D) The area in which antibiotics are inhibited from killing bacteria

The area around the antibiotic disk in which bacteria cannot grow

What characteristic of the Kirby-Bauer test helps scientists to determine if a microorganism is susceptible to an antibiotic? A) The size of the colonies the organism forms B) The ability of the microorganism to degrade the agar around the antibiotic disks. C) The diameter of the zone of inhibition surrounding the antibiotic disks D) A pH change that alters the color of the agar surrounding the antibiotic disk

The diameter of the zone of inhibition surrounding the antibiotic disks

Which of the following characteristics does NOT need to be standardized in a Kirby-Bauer assay? A) The number of bacteria plated B) The method used to develop a bacterial lawn on the agar plate C) The thickness of the agar D) The size of the antibiotic disk

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

What does the Kirby-Bauer test assess? A) The ability of a microorganism to secrete an antibiotic B) The susceptibility of an organism to a set of antibiotics C) The ability of an organism to mutate in the presence of an antibiotic D) The ability of a microorganism to swim away from an antibiotic

The susceptibility of an organism to a set of antibiotics

Most known bacteria that have been cultured from human skin are Gram-positive A) True B) False

True

A greenish area around a bacterial colony growing on blood agar indicates _______________. A) gamma-hemolysis B) fermentation C) alpha-hemolysis D) bacitracin sensitivity E) beta-hemolysis

alpha-hemolysis

To test for a microbe's ability to produce an enzyme that clots blood fibrin, clumping will be observed after adding _____________________. A) coagulase plasma B) catalase C) antigens D) mannitol E) hydrogen peroxide

coagulase plasma

What color is phenol red in the presence of acid? A) blue B) yellow C) green D) red E) black

yellow