BIOL 351 EXAM 3 2026-2027 QUESTIONS
AND CORRECT ANSWERS GRADED A+
When observing for lysine decarboxylation in LIA, do you observe the slant or the
butt?
Butt
When observing for lysine deamination in LIA, do you observe the slant or the
butt?
Slant
If an organism can undergo lysine decarboxylation, what color and where can you
observe this reaction in LIA?
Purple; Butt
If an organism can undergo lysine deamination, what color and where can you
observe this reaction in LIA?
Red; Slant
What is the interpretation for a purple slant / purple butt in LIA?
Positive lysine decarboxylase and negative lysine deamination
,What is the interpretation for a purple slant / yellow butt in LIA?
Negative lysine decarboxylase and negative lysine deamination
What is the interpretation for a red slant / yellow butt in LIA?
Negative lysine decarboxylase and positive lysine deamination
What is the purpose of the oxidase test?
To identify bacteria containing cytochrome c oxidase
What is the resultant color in a positive oxidase test and what molecule is oxidized
to form this color?
Purple/blue color; Tetramethyl-p-phenylenediamine
What is the purpose of the catalase test?
To identify organisms that produce the enzyme catalase
The catalase test is most commonly used to differentiate between what members?
Catalase-positive Staphylococceae and Micrococcaceae from the catalase-negative
Staphylococceae
, What indicates a catalase positive test meaning that the enzyme catalase is present?
The formation of bubbles after the addition of hydrogen peroxide
What is the purpose of using Phenol Red broth?
To differentiate members of Enterobacteriaceae from other gram-negative rods
A differential test medium prepared as a base with a carbohydrate added
Is Phenol Red broth selective/differential/both? What makes it that way?
Phenol Red broth is differential; It contains a pH indicator (Phenol Red) which is
yellow under acidic conditions and red under basic conditions
What reaction must undergo to form acid byproducts? What reaction must undergo
to form basic byproducts?
Carbohydrate fermentation form acid byproducts; Deamination of peptone amino
acids form ammonia which is a basic by product
How is the presence of gas production measured in Phenol Red broth?
A Durham tube is added
True/False: Methyl Red, Voges-Proskauer is mutually exclusive.
AND CORRECT ANSWERS GRADED A+
When observing for lysine decarboxylation in LIA, do you observe the slant or the
butt?
Butt
When observing for lysine deamination in LIA, do you observe the slant or the
butt?
Slant
If an organism can undergo lysine decarboxylation, what color and where can you
observe this reaction in LIA?
Purple; Butt
If an organism can undergo lysine deamination, what color and where can you
observe this reaction in LIA?
Red; Slant
What is the interpretation for a purple slant / purple butt in LIA?
Positive lysine decarboxylase and negative lysine deamination
,What is the interpretation for a purple slant / yellow butt in LIA?
Negative lysine decarboxylase and negative lysine deamination
What is the interpretation for a red slant / yellow butt in LIA?
Negative lysine decarboxylase and positive lysine deamination
What is the purpose of the oxidase test?
To identify bacteria containing cytochrome c oxidase
What is the resultant color in a positive oxidase test and what molecule is oxidized
to form this color?
Purple/blue color; Tetramethyl-p-phenylenediamine
What is the purpose of the catalase test?
To identify organisms that produce the enzyme catalase
The catalase test is most commonly used to differentiate between what members?
Catalase-positive Staphylococceae and Micrococcaceae from the catalase-negative
Staphylococceae
, What indicates a catalase positive test meaning that the enzyme catalase is present?
The formation of bubbles after the addition of hydrogen peroxide
What is the purpose of using Phenol Red broth?
To differentiate members of Enterobacteriaceae from other gram-negative rods
A differential test medium prepared as a base with a carbohydrate added
Is Phenol Red broth selective/differential/both? What makes it that way?
Phenol Red broth is differential; It contains a pH indicator (Phenol Red) which is
yellow under acidic conditions and red under basic conditions
What reaction must undergo to form acid byproducts? What reaction must undergo
to form basic byproducts?
Carbohydrate fermentation form acid byproducts; Deamination of peptone amino
acids form ammonia which is a basic by product
How is the presence of gas production measured in Phenol Red broth?
A Durham tube is added
True/False: Methyl Red, Voges-Proskauer is mutually exclusive.
