Question

bio2010-fall 2025 lab quiz #6-. module 17-module 18. total 10 points
select one best choice. write your answer on the answer sheet provided. organism names
must be written in binomial nomenclature and correctly spelled.

1. in general, the larger the zone of inhibition

on mueller hinton media, the organism is:
a. more sensitive
b. more resistant

1. the production of which of the following

may be responsible for bacterial resistance
to penicillin?
a. beta lactamase
b. beta lactam
c. peptidoglycan

1. which of the following is targeted by

antimicrobial drugs?
a. fungal infections
b. bacterial infections
c. viral infections
d. b and c

1. penicillin is more effective in killing:

a. gram negative bacteria
b. gram positive bacteria
c. penicillin-resistant bacteria

1. the diffusion rate of antibiotics on the

mueller hinton media is determined by the
following factors, except:
a. the molecular weight of the
antibiotics
b. the size of antibiotic disks
c. concentration of the antibiotics
bonus: the name of the antimicrobial
susceptibility test that was done in our lab is

1. emb plate is selective but not differential

a. true.
b. false

1. the targets of antibiotics include the

following, except:
a. dna replication
b. protein synthesis
c. glucose synthesis
d. cell wall synthesis

1. the presumptive mpn test looks for the

presence of:
a. escherichia coli
b. enterobacter aerogenes
c. enteric bacteria
d. coliforms

1. metallic sheen on colonies growing on an

emb plate indicates that the organism:
a. is a gram negative
b. uses metal in metabolism
c. ferments lactose
d. is resistance to bile

1. you inoculated 3 sets of lactose tubes with

10ml, 1 ml, and 0.1 ml of water sample.
after incubation the only that turned yellow
and produce gas were the 5 tubes inoculated
10 ml samples. what is the most probable
number of bacteria present in this water
sample? (see mpn chart on the next page if
needed)
a. 23 cfu/100 ml
b. 23 cfu/ml
c. 240 cfu/100 ml
d. 240 cfu/ml
e. cannot be determined

Explanation:

1. Larger zones of inhibition indicate greater sensitivity to antibiotics.
2. Beta-lactamase breaks down penicillin’s beta-lactam ring, causing resistance.
3. Antimicrobial drugs target bacteria and fungi; viruses are not targeted by typical antimicrobials.
4. Penicillin disrupts peptidoglycan (thicker in Gram-positive bacteria), making them more susceptible.
5. Antibiotic disk size does not affect diffusion rate (molecular weight, concentration, and media properties do).
6. EMB plates are both selective (for Gram-negatives) and differential (distinguishes lactose fermenters).
7. Antibiotics target DNA replication, protein synthesis, and cell wall synthesis; glucose synthesis is not a common target.
8. The presumptive MPN test detects coliforms (indicator of fecal contamination).
9. Metallic sheen on EMB plates is characteristic of strong lactose fermenters (e.g., E. coli).
10. MPN requires results from all three dilutions (10mL, 1mL, 0.1mL) to calculate; only 10mL results are given, so it cannot be determined.

Bonus: The Kirby-Bauer test is the standard antimicrobial susceptibility test using Mueller-Hinton media.

Answer:

1. A. More sensitive
2. A. Beta lactamase
3. A. Fungal infections (Note: This is a correction—antimicrobials include antifungals; if "antibiotics" were specified, B would be correct, but the question says "antimicrobial drugs")
4. B. Gram positive bacteria
5. B. The size of antibiotic disks
6. B. False
7. C. Glucose synthesis
8. D. Coliforms
9. C. Ferments lactose
10. E. Cannot be determined

Bonus: Kirby-Bauer test