Lab Quiz 7: API 20 E, Catalase, and Nitrate Reduction

Comprehensive vocabulary flashcards covering the API 20 E test strip, catalase test, and nitrate reduction test including substrates, enzymes, products, and reagents.

API 20 E Purpose

For rapid identification of Enterobacteriaceae and other gram-negative rods.

Exoenzyme

Enzymes that are transported extracellularly, where they break down large food molecules or harmful chemicals.

Endoenzyme

Enzymes that are retained intracellularly and function there.

API 20 E Exoenzymes

The two exoenzymes tested in the API 20 E strip are Urease and Gelatinase.

Phenol red

A pH indicator used in ADH, LDC, ODC, and URE microtubes; it is yellow below pH $6.8$ (acidic) and red/pink above pH $7.4$ (alkaline).

Bromthymol blue

A pH indicator used in [CIT] and all sugar tubes; it is yellow below pH $6.8$ (acidic) and blue above pH $7.6$ (alkaline).

ONPG (O-nitrophenyl-$\beta$-D-galactopyranoside)

The substrate used to determine if bacteria produce the endoenzyme $\beta$-galactosidase.

O-nitrophenol

The detected yellow end product of the ONPG test produced when $\beta$-galactosidase hydrolyzes ONPG.

Arginine Dehydrolase (ADH)

An endoenzyme that breaks down the amino acid substrate Arginine into alkaline products, turning phenol red to red.

Lysine Decarboxylase (LDC)

An endoenzyme that decarboxylates the amino acid substrate Lysine into the detected product cadaverine.

Cadaverine

The detected end product of the Lysine Decarboxylase (LDC) test.

Ornithine Decarboxylase (ODC)

An endoenzyme that decarboxylates the amino acid substrate Ornithine into the detected product putrescine.

Putrescine

The detected end product of the Ornithine Decarboxylation (ODC) test.

Pyridoxyl phosphate

A cofactor activated by acids (produced during anaerobic fermentation) that is required for the LDC and ODC tests.

Citrate [CIT] Purpose

To determine whether bacteria can utilize Citrate as a sole carbon source using the endoenzyme citrase.

Hydrogen Sulfide (H2S) Test

A test to determine if bacteria produce thiosulfate reductase; it utilizes the reagent Ferrous Ammonium Sulfate to detect $H_2S$ as a black precipitate.

Urease (URE)

An exoenzyme that hydrolyzes Urea into the alkaline product $NH_3$, resulting in a bright pink color with phenol red indicator.

Tryptophan Deaminase (TDA)

An endoenzyme that deaminates the substrate Tryptophan into the product indole-pyruvic acid.

Ferric Chloride ($FeCl_3$)

The reagent added to the TDA microtube that turns red-brown in the presence of indole-pyruvic acid.

Tryptophanase

The endoenzyme that produces the detected product indole from the amino acid substrate Tryptophan.

Kovac’s Reagent

The reagent added to the Indole (IND) test that turns red-copper in a positive result.

Voges-Proskauer [VP] Substrate

Sodium Pyruvate, which bacteria ferment to produce the detected end product acetoin.

VP Reagents

VPa ($\alpha$-naphthol) and VPb (KOH, Potassium hydroxide) added to the [VP] cupule.

Gelatinase [GEL]

An exoenzyme that hydrolyzes the large protein substrate gelatin; a positive result is indicated by the medium turning liquid or black.

Carbohydrate Fermentation (GLU, MAN, INO, SOR, etc.)

The process of breaking down specific carbohydrates into acids, turning the pH indicator Bromthymol Blue from blue to yellow.

Catalase Function

An endoenzyme that breaks down the substrate hydrogen peroxide ($H_2O_2$) into the products $O_2(g)$ and $H_2O$.

Catalase Positive Result

The presence of bubbles after adding hydrogen peroxide ($H_2O_2$) to the MAN, INO, or SOR microtubes.

Nitrate Reduction Reagents

Reagent A (sulfanilic acid) and Reagent B ($\alpha$-naphthylamine), which are added to the GLU tube to detect nitrite.

Nitrate Reductase

The enzyme that reduces nitrate ($NO_3$) to nitrite ($NO_2$).

Zinc (Nitrate Test)

A powerful reducing agent added if no color change occurs after Reagents A and B; if the tube turns red after zinc, the result is negative for nitrate reduction.

Full Nitrate Reduction

A positive result where bacteria produce both nitrate reductase and nitrite reductase, indicated by no color change even after adding zinc.

Anaerobic Environment in API 20 E

Created by adding oil to the ADH, LDC, ODC, H2S, and URE tubes.