MICROBIOLOGY EXAM QUESTIONS AND ANSWERS ON ANTIBIOTICS

MICROBIOLOGY EXAM QUESTIONS
AND ANSWERS ON ANTIBIOTICS
What is an antibiotic?
A. An organism that inhibits the growth of other organisms
B. A chemical that inhibits microbial growth
C. A synthetic chemical that kills bacteria
D. All available answers are characteristics of an antibiotic.
B
What does the Kirby-Bauer test assess?
A. The ability of a microorganism to swim away from an
antibiotic
B. The ability of a microorganism to secrete an antibiotic
C. The ability of an organism to mutate in the presence of an
antibiotic
D. The susceptibility of an organism to a set of antibiotics
D
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. Do different antibiotics diffuse the same distance through
agar?
C. Is a particular bacterium susceptible to any of a variety of

,antibiotics?
D. All available answer choices are possibilities.
C
What characteristic of the Kirby-Bauer test helps scientists to
determine if a microorganism is susceptible to an antibiotic?
A. The diameter of the zone of inhibition surrounding the
antibiotic disks
B. A pH change that alters the color of the agar surrounding
the antibiotic disk
C. The ability of the microorganism to degrade the agar
around the antibiotic disks
D. The size of the colonies the organism forms
A
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
B
Which of the following characteristics does NOT need to be
standardized in a Kirby-Bauer assay?
A. The method used to develop a bacterial lawn on the agar

,plate
B. The thickness of the agar
C. The number of bacteria plated
D. The size of the antibiotic disk
A
Why is it critical to use aseptic technique when transferring
the antibiotic disks to the agar?
A. All available answers are correct.
B. Contaminating organisms could produce their own
antibiotics.
C. Contaminating microorganisms could break down the
antibiotics.
D. Contaminating microorganisms could alter the diffusion of
the antibiotics through the agar.
A
What are the three possible outcomes for each antibiotic:
microorganism pair in a Kirby-Bauer assay?
A. Similar, reversion, or indeterminate
B. Susceptible, resistant, or indeterminate
C. Susceptible, resistant, or intermediate
D. Stunted, robust, or intermediate
C
You perform a Kirby-Bauer assay with two antibiotics.
Antibiotic X has a zone of inhibition of 9 mm. Antibiotic Y has
a zone of inhibition of 11 mm. Which antibiotic is better at

, killing this particular microorganism?
A. Antibiotic Y
B. It is impossible to tell from the information given.
C. Antibiotic X and Y, which have identical antimicrobial
activities
D. Antibiotic X
B
You perform a Kirby-Bauer assay, but you neglect to use
aseptic technique. Your plate becomes contaminated with a
bright red organism. You can easily tell this organism apart
from the one you intended to inoculate (which has grown into
a nice lawn all over the plate). In order to conserve time, you
measure the zone of inhibition for your intended organism,
ignoring the contaminants. Are you assured to get the correct
answer using this method?
A. No, the contaminant adds too many variables to make this
assay usable.
B. Yes, but you have to factor in the zone of inhibition for the
contaminant as well.
C. Yes, but you would have to subtract 1-2 mm from the
intended organism's zone of inhibition to account for the
presence of the contaminant.
D. Yes, you can easily tell the two organisms apart, ensuring
that you measure only the zone of inhibition for the correct
organism.
A