MICROBIOLOGY LAB EXERCISES EXAM QUESTIONS
AND ANSWERS #20
The type of metabolism occurring when microorganisms incompletely oxidize sugars,
resulting in valuable byproducts such us ethyl alcohol and organic acids, yet very little
ATP is made - correct answer Fermentation
Nitrite reduction is a useful biochemical test for identifying bacteria. During this
metabolic process nitrate serves as a final electron acceptor, an a moderate amount of
ATP is produced. This type of metabolism is know as: - correct answer Anaerobic
respiration
The enzyme produced and excreted by some bacteria to break down relatively large
and insoluble starch molecules into soluble units of glucose - correct answer
Extracellular amylases
Which of the following types of microorganisms is least likely to produce extracellular
enzymes (exoenzymes)? - correct answer Bacteria, e.g. E.coli that live in human
intestine
A positive sugar fermentation test will be detected by_____ (a yellow color) and/or____
(an air bubble in the Durham tube) production. - correct answer Acid; gas
A positive nitrate reduction test is indicated by the development of a ______ color
following the addition of the nitrite detecting reagents (2 drops of sulfanilic acid followed
by 6 drops of naphthylamine) - correct answer Red
In this week's lab you will spit on an unused portion of the E. Coli side of your control
starch plate. Why? - correct answer To demonstrate the presence of the starch
hydrolyzing enzyme (alpha-amylase) in human saliva
These Gram negative, non-sporeforming, rod-shaped, and lactose-fermenting bacteria
are indicators of unsafe contamination of food or water - correct answer Coliforms
Which of the following statements is/are true regarding Eosin Methylene Blue (EMB)
agar? - correct answer It is used for the confirmed test of water
It is selective and differential
It inhibits growth of gram positive and selects for growth of gram negative
The material, typically a sterile liquid, with which a sample is diluted - correct answer
Diluent
If 1ml of diluate (a.k.a. Aliquot) is added to 9ml of diluent, what is the dilution? - correct
answer 1:10
, Exoenzyme produced to break down starch? Breaks down into? - correct answer alpha-
amylase
Glucose and maltose
Exoenzyme produced to break down casein? Breaks down into? - correct answer
Caseinase
Amino acids
Bromcresol purple colors? - correct answer Yellow-Acidic ph
Purple-Neutral ph
Nitrate reduction to nitrite? - correct answer Turns from yellow to red
Red is positive, yellow is negative
B. Polymyxa exoenzyme production - correct answer Positive
E. Col exoenzyme production - correct answer Negative
Waterborne diseases include - correct answer Typhoid fever, cholera, viral diseases,
dysentery, giardiasis, parasitic diseases
Why can pathogens responsible for waterborne illnesses be hard to detect - correct
answer Present in low numbers
Fastidious (requires special media)
Too much variety
What are used as indicators of contamination in water? - correct answer Coliform
Coliform bacteria characteristics - correct answer Gram negative
Non-sporulating rods
Ferment lactose to acid and gas within 48 hours at 35C
Fecal coliforms - correct answer Found in intestinal tract of warm-blooded animals
(sewage)
Non-fecal coliforms - correct answer Found in soil and plant material
Presumptive test - correct answer Looks for lactose fermenters
Confirmed test - correct answer EMB agar confirms presence of lactose fermenters and
gram negative
Completed test - correct answer NA slant and lactose broth checks for gram negative
non sporulating rods that ferment lactose
EMB agar - correct answer Eosin Methylene Blue Agar
AND ANSWERS #20
The type of metabolism occurring when microorganisms incompletely oxidize sugars,
resulting in valuable byproducts such us ethyl alcohol and organic acids, yet very little
ATP is made - correct answer Fermentation
Nitrite reduction is a useful biochemical test for identifying bacteria. During this
metabolic process nitrate serves as a final electron acceptor, an a moderate amount of
ATP is produced. This type of metabolism is know as: - correct answer Anaerobic
respiration
The enzyme produced and excreted by some bacteria to break down relatively large
and insoluble starch molecules into soluble units of glucose - correct answer
Extracellular amylases
Which of the following types of microorganisms is least likely to produce extracellular
enzymes (exoenzymes)? - correct answer Bacteria, e.g. E.coli that live in human
intestine
A positive sugar fermentation test will be detected by_____ (a yellow color) and/or____
(an air bubble in the Durham tube) production. - correct answer Acid; gas
A positive nitrate reduction test is indicated by the development of a ______ color
following the addition of the nitrite detecting reagents (2 drops of sulfanilic acid followed
by 6 drops of naphthylamine) - correct answer Red
In this week's lab you will spit on an unused portion of the E. Coli side of your control
starch plate. Why? - correct answer To demonstrate the presence of the starch
hydrolyzing enzyme (alpha-amylase) in human saliva
These Gram negative, non-sporeforming, rod-shaped, and lactose-fermenting bacteria
are indicators of unsafe contamination of food or water - correct answer Coliforms
Which of the following statements is/are true regarding Eosin Methylene Blue (EMB)
agar? - correct answer It is used for the confirmed test of water
It is selective and differential
It inhibits growth of gram positive and selects for growth of gram negative
The material, typically a sterile liquid, with which a sample is diluted - correct answer
Diluent
If 1ml of diluate (a.k.a. Aliquot) is added to 9ml of diluent, what is the dilution? - correct
answer 1:10
, Exoenzyme produced to break down starch? Breaks down into? - correct answer alpha-
amylase
Glucose and maltose
Exoenzyme produced to break down casein? Breaks down into? - correct answer
Caseinase
Amino acids
Bromcresol purple colors? - correct answer Yellow-Acidic ph
Purple-Neutral ph
Nitrate reduction to nitrite? - correct answer Turns from yellow to red
Red is positive, yellow is negative
B. Polymyxa exoenzyme production - correct answer Positive
E. Col exoenzyme production - correct answer Negative
Waterborne diseases include - correct answer Typhoid fever, cholera, viral diseases,
dysentery, giardiasis, parasitic diseases
Why can pathogens responsible for waterborne illnesses be hard to detect - correct
answer Present in low numbers
Fastidious (requires special media)
Too much variety
What are used as indicators of contamination in water? - correct answer Coliform
Coliform bacteria characteristics - correct answer Gram negative
Non-sporulating rods
Ferment lactose to acid and gas within 48 hours at 35C
Fecal coliforms - correct answer Found in intestinal tract of warm-blooded animals
(sewage)
Non-fecal coliforms - correct answer Found in soil and plant material
Presumptive test - correct answer Looks for lactose fermenters
Confirmed test - correct answer EMB agar confirms presence of lactose fermenters and
gram negative
Completed test - correct answer NA slant and lactose broth checks for gram negative
non sporulating rods that ferment lactose
EMB agar - correct answer Eosin Methylene Blue Agar
