Microbiology

Reagents


Diverse biochemical reagents are known for determining certain metabolisms and to differentiate the bacteria.

Still often classical biochemical tests are used to determine microorganisms. The result can be seen by a color change. Most reactions are based on the detection of an enzyme with a certain given substrate. Also methods to detect certain metabolites by chemical reaction and or complex building techniques are used. At the end a color change gives a result which leads to more cognition of the unknown organism (see table 1).

Cat. No.
Detection of
Differentiation of Organisms
Reaction
Color
(by positive result)
Reagent
29333
39442
acetoin production
Klebsiella, Enterobacter oxidize acetoin, reacts with alpha-naphtol red Barritt's Reagent A Barritt's Reagent B
07689
acetoin production
Klebsiella, Enterobacter oxidize acetoin, reacts with alpha-naphtol red O'Meara's Reagent
38497
39441
nitrate reduction to nitrite
Enterobacter, E. coli, Salmonella reacts with sulphanilic acid, forms a azo dye with alpha-naphtylamine red Nitrate Reagent A Nitrate Reagent B
07345

07817
oxidase activity
oxidase positives, oxidase negatives oxidize dimethyl-p-phenylenediamine hydrochloride, build a complex with alpha-naphtol dark blue Oxidase Reagent acc. Gaby-Hadley A
Oxidase Reagent acc. Gaby-Hadley B
18502
oxidase activity
oxidase positives, oxidase negatives oxidize N,N-dimethyl-p-phenylenediamine to Wurster's blue dark blue-purple Oxidase Reagent acc. Gordon-McLeod
08714
strong acid production
E. coli, Enterobacter indicator reaction red Methyl Red Solution
80353
tryptophan deaminase activity
Proteus reacts with indolepyruvic acid dark brown TDA Reagent
49825
tryptophanase activity
E. coli reacts with indole blue-purple DMACA Reagent
60983
67309
tryptophanase activity
E. coli reacts with indole red Kovac's Reagent for indoles
Kovac's Reagent for indoles
table 1: Biochemical Tests


Application example: Oxidase Reagents acc. Gaby-Hadley

These reagents can be used to perform the cytochrome c oxidase test in different methods. To differentiate organisms based on the presence of cytochrome c oxidase is one of the first and most important step by the identification of bacteria. The cytochrome c oxidase present in most gram negative bacteria oxidize dimethyl-p-phenylenediamine and alpha-naphtol a dark blue complex (indophenol blue). The test is applicable on agars in broths and on discs (see figure 1-4). Important is to do a positive and negative control with the samples.

Instructions:
Grow test culture on nutrient agar slant (18-24 hours). Add 2-3 loops of reagents A and B to slant.
Tilt tube to permit reagents to mix and flow over growth.

Result:
Observe for color change. A positive reaction shows a dark purple blue color on growth, especially at the border of the colonies, within 2 minutes.



Figure 1: E. coli on a agar plate
Figure 2: Pseudomonas flourescence on a agar plate


 

Figure 3: paper discs impregnated with 2 drops of each reagent:
left disc with E. coli;
right disc with Pseudomonas flourescence
Figure 4: cultures with 2 drops of each reagent:
left tube with E. coli;
right tube with Pseudomonas fluorescence



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