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MIBO 3510L - Exam 2/Practical 1 Study Guide

Terms in this set (72)

Identifies Gram-negative enteric pathogens

**TEST realistically helps you determine if the bacteria contain Lysine Decarboxylase or Lysine Deaminase enzymes**

Four Differential Tests:

1) Fermentation of glucose (include pH indicator == Bromocresol purple)

Purple = pH > 6.8 (K)
Yellow = acidic, pH < 5.2 (A)

Little glucose is added (like TSI) - fermenters K/A.

2) Production of H2S (via Fe test as in SIM media)
Look for formation of a black precipitate

3) Lysine decarboxylase: following fermentation (requires acid), decarboxylation of lysine raises the pH and turns the butt purple

4) Lysine deaminase: lysine deamination products react with ferric ammonium citrate and turn the slant red


Starting color: purple


~10 hrs:

Fermenters of glucose: whole tube is yellow


~24 hrs:

Sugar reaction: glucose has run out, aerobic utilization of amino acids turns slant purple (K), anaerobic butt remains yellow (A)

(Bacteria can ferment glucose but does not contain lysine decarboxylase or lysine deaminase)


Lysine decarboxylase producers (must also ferment glucose): slant turns purple as described above, butt turns purple due to anaerobic lysine decarboxylation

(Bacteria can ferment glucose, and also produce lysine decarboxylase, causing the slant to turn purple (K) after glucose is gone, but also causing the butt to turn purple (K) due to basic products of lysine decarboxylation


Lysine deaminase producers: slant turns red due to aerobic lysine deamination (does not happen anaerobically)

(Bacteria can ferment glucose giving it a yellow butt, and the bacteria also produce lysine deaminase enzymes that turn the slant red)


H2S producers: H2S reaction with iron results in black precipitate forming (may or may not fill entire butt of tube)

Gas producers: Cracks form in butt of tube


***Note: If organism does not ferment glucose, H2S and lysine decarboxylase are not readable!!!

**Lysine decarboxylase would not be readable if organism doesn't ferment glucose because since LIA tubes start out purple in color and lysine decarboxylase produces a purple butt due to basic byproducts of lysine decarboxylation, so there would be no way to tell if an organism had lysine decarboxylase enzymes since the tube would still be purple due to no acidic byproducts of glucose fermentation to change it to be yellow butt