Micro Biochem Tests- GNR

Oxidase

• Tests for Cytochrome C Oxidase

• Pos (Blue): Pseudomonas

• Neg: Enterobacteriacae

Spot Indole

• Tests for tryptophanase

• Pos (Blue): E.coli, Klebsiella oxytoca, Proteus Vulgaris, Citrobacter koseri, Morganella morganii

• Neg: Klebsiella pneumoniae, Proteus mirabilis, Salmonella, Shigella, Pseudomonas aeruginosa

PYR

• Tests for pyrolidonyl arylamidase/ aminopeptidase

• Pos: Klebsiella, Citrobacter, Serratia, Enterobacter, Yersinia

• Neg: E.coli

OF Media

-Covered (Anaerobic): Tests for fermentation

-Uncovered (Aerobic): Tests for oxidation

Triple Sugar Iron (TSI) Slants

• Tests for sugar fermentation (glucose, sucrose, lactose) K= red A= yellow and H2S production

• K/K: no fermentation- Pseudomonas aeruginosa

• K/A: glucose fermentation only- Salmonella, Shigella

• A/A: glucose, lactose and/or sucrose fermentation- E.coli, Proteus vulgaris

• Black: H2S production- Salmonella

• Bubbles/ Cracks: Gas production- Salmonella

Kliger Iron Agar (KIA)

• Same as TSI, but without Sucrose

• Results same as TSI, unless organism is a NLF, but can ferment sucrose- Proteus vulgaris (K/A)

ONPG

• Tests for delayed Lactose fermentation (organisms that have Beta-galactosidase, but not permease)

• Pos (Yellow): E.coli, Enterobacter aerogenes

• Neg: Proteus mirabilis

Methyl Red (MR)

• Tests for mixed acid end product (messy girl)

• Always done with VP

• Pos: Produces red color change

Voges- Proskauer (VP)

• Tests for 2,3- Butanediol (clean girl)

• Always done with MR

• Pos: Produces red color change

Arginine/Lysine/Onithine Decarboxylase (ADC/LDC/ODC) (AKA Moeller’s Method)

• Detects the production of the corresponding enzyme from the organism used for hydrolyzation of an AA, producing an alkaline environment

• Organism must be a glucose fermenter for reaction

• Positive reaction produces purple end product

Arginine Decarboxylase (ADC)

• Pos (Purple): Pseudomonas aeruginosa, Vibrio cholerae, E.coli (Variable), Salmonella (delayed/ neg), Shigella (delayed/ neg)

• Neg (Yellow): Enterobacter aerogenes, Klebsiella pneumo, Proteus vulgaris, Serratia, E.coli (Variable), Salmonella (delayed pos/ neg), Shigella (delayed pos/ neg)

Lysine Decarboxylase (LDC)

• Pos (Purple): Enterobacter aerogenes, Klebsiella pneumo, Salmonella, Serratia, E.coli (variable)

• Neg: Proteus vulgaris, Pseudomonas aeruginosa, Shigella, Vibrio cholerae

Ornithine Decarboxylase (ODC)

• Pos (Purple): Enterbacter aerogenes, Serratia, Vibrio cholera, E.coli (variable)

• Neg: Klebsiella pneumo, Proteus vulgaris, Pseudomonas aeruginosa, Salmonella, Shigella, E.coli (variable)

Phenylalanine Deaminase (PAD)

• Detects the presence of phenylalanine deaminase used to from phnylpyruvic acid

• Pos (Green): Proteus, Morganella, Providencia sp.

Citrate Utilization

• Tests whether citrate can be used as the organism’s source of carbon using Simmon’s citrate medium (ammonia salts + citrate+ bromothmol blue)

• Color change by bacteria using bile salts to create ammonia

• Pos (Blue): Klebsiella, Enterobacter, Salmonella, possibly Citrobacter

• Neg (no color change- green): E.coli

Urease

• Tests for an organism’s ability to hydrolyze urea

• Differentiates Proteus sp from NLF Enterobacteria

• Pos: Proteus sp (Strongly positive)

• Neg: E.coli, other NLF Enterobacteria

Nitrate Reduction Test

• Tests for an organism’s ability to reduce nitrate to nitrite using nitroreductase

• It is possible that an organism can reduce nitrate all the way to N gas, producing a false negative result

  • Zinc is added to negative results to confirm, if color changes after Zinc addition, falsehood is upheld

• Nitrite Pos (Color change before Zinc): All Enterobacterales should be

• Nitrite Neg (No color change before Zinc, color change after Zinc): No Relevant Examples

• N Gas Pos (No color change after Zinc): Variable

Gelatin Liquefaction

• Detects presence of gelatinase enzyme, causing liquification of medium gelatin

• Pos (Liquification): Proteus and Serratia sp, Stenotrophomonas maltophilia

• Neg: (No Liquification): E.coli

Motility

• Tests for motile enteric bacteria, motile organisms diffuse into agar

• Pos (Turbidity in agar): E.coli, Enterbacter, Citrobacter, Salmonella, Serratia

• Neg: Klebsiella

Full ID for Differentiating GNR

• A giant test kit that includes all the tests to differentiate GNRs

• This gives you a number that you input on a computer and it gives you a percentage likelihood of the sample being whatever species it may be

• Rapid test