lab quiz 1

What bacteria were involved in the phenylalanine deaminase lab?

Escherichia coli Proteus mirabilis

what are the indicators for the deamination and sulfur reduction

Ferric ammonium citrate

In lab 5-12 Phenylalanine deaminase we inoculate the slants using what method?

Fish tail streak

Describe the reaction when you see a black precipitate

Hydrogen sulfide (H2S) is produced in lysine iron agar by the anaerobic reduction of thiosulfate.

What is going on if there is a purple slant/ butt if our control is purple too?

If the medium has been inoculated with a lysine decarboxylase-positive organism, acid production from glucose fermentation will induce production of decarboxylase enzymes. The acidic pH will turn the medium yellow, this triggers decarboxylation of lysine, which will produce Cadaverine and alkalinize the agar= returning it to purple.

Describe the reaction when you see a red slant/ yellow butt

If the organism produces lysine deaminase, the resulting deamination reaction will produce compounds that react with the ferric ammonium citrate and produce a red color. Yellow because the butt is in an anaerobic region, with no oxygen.

What bacteria is used in the Lysine Iron Agar lab?

1. Enterobacter aerogenes 2. Citrobacter freundii 3. Proteus mirabilis

What bacteria are used in the DNAse lab?

1. Serratia marcescens 2. Escherichia coli

What pH is phenol red when it is yellow?

6.8 for yellow

What are the indicators for decarboxylation and glucose fermentation in the LIA lab?

Bromocresol purple

How is fermentation detected in this test?

If the phenol red broth medium turns yellow, that means there was fermentation of sugar, there was acid production. If it is red with no bubble, means there was no fermentation. If pink, it means there was degradation of peptone; alkaline end products.

What is the indicator for the phenylalanine deaminase lab?

Indicator is Ferric Chloride ions (FeCl3), it reacts with phenyl pyruvic acid to show a positive result, green color.

What is the purpose of the LIA lab?

Looking for lysine decarboxylation, lysine deamination, glucose fermentation, and production of hydrogen sulfide gas

What does purple slant with yellow butt mean?

Lysine deaminase negative; lysine decarboxylase negative; glucose fermentation positive because there is no oxygen at the bottom of slant; K/A.

purple slant/ purple butt

Lysine deaminase negative; lysine decarboxylase positive; K/K.

Red slant/ yellow butt

Lysine deaminase positive; lysine decarboxylase negative; glucose fermentation R/A

What is the indicator for the DNA hydrolysis test?

Methyl Green dye is added to the DNA rich agar to act as our indicator for the DNA hydrolysis test.

What is the indicator for the Phenol Red broth test?

Phenol Red

Phenylalanine deaminase is present in certain bacteria. In your own words, explain what this enzyme catalyzes.

Phenylalanine Deaminase removes NH2, an amine group from phenylalanine (amino acid). Next, two hydrogen ions will be removed, these ions plus water produce an intermediated acid. Intermediated acid undergoes deamination (removes NH2) to make NH3 (ammonia), and phenyl pyruvic acid.

What is the purpose of the DNAse lab?

Purpose is to identify the bacteria that produce DNAse (enzyme, that breaks down DNA into small fragments called nucleotides, hydrolyzes DNA)

For the DNAse lab, which bacteria gave a positive result?

Serratia marcescens

Black precipitate

Sulfur reduction; H2S.

What is the purpose of the Phenol Red Broth lab?

The purpose of the phenol red broth lab is to look for fermentation of sugar, specifically glucose, sucrose, and lactose.

What happened in the DNA hydrolysis test?

The bacteria Serratia marcescens was the positive result. Serratia marcescens was able to produce the exoenzyme DNase which hydrolyzed the DNA rich agar into it nucleotide subunits.

What is the purpose of the phenylalanine deaminase lab?

To see which organism produces the enzyme phenylalanine deaminase.

What pH is phenol red when it turns red?

above 7.4 for red, this is neutral

What pH is phenol red when it turns pink?

above 8 when it turns pink