Advances in culture media design (Chromogen and Inhibigen compounds)

Neal Parker

Industrial account manager

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Introduction

• Background and principles of Chromogens

• Why do we use them?

• Background and principles of Inhibigens

• Why do we use them?

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Background and principles of chromogenic media

• Chromogen – “a chemical compound, itself without colour, that can be transformed into a coloured compound, or can react with another material to form a coloured compound”

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E. coli

Chromophore component (e.g. indoxyl derivative such as 5-bromo-4-chloro-3-indoxyl)

Sugar component (e.g. galactose)

Uptake

Enzyme

Chromogen

Background and principles of chromogenic media

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Background and principles of chromogenic media

E. coli

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O

OH

H

H

HO

H

H

OHHO

OH

NH

O

OH

H

H

HO

H

H

OHHOH

OH

HN

NH

O

O

Cl

Br

Cl

Br

Cl

Br

-galactosidase oxidation

5-bromo-4-chloro-3-indoxyl--D-galactopyranoside (X-Gal)

galactose blue-turquoise chromophore

Background and principles of chromogenic media

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Why use Chromogens?

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Why use Chromogens?

• Improve overall specificity of a diagnostic medium.

• Positive colonies are easy to identify.

• Reduce number of sub-cultures required.

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Current chromogen situation

• The large scale synthesis of chromogens means compounds are affordable for use in culture media

• There are now chromogenic media available for almost all organisms of interest in both the Industrial and Clinical environments

• >30 chromogenic media formulations are currently available for the differentiation of E. coli and coliforms

• >10 formulations for Salmonella

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From chromogens to inhibigens…

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Background and principles of Inhibigens

• Inhibigen – “an inhibitor molecule linked to a specific substrate. In this bound state, the inhibitor is non-toxic. However, if taken up by a cell and cleaved from the substrate, the Inhibigen molecule will prevent the organism from replicating ”

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Uptake

Inhibition of cell wall synthesis

Loss of viability

Inhibitor component (AEP)

Sugar or amino acid component

InhibigenTM

Specific enzyme hydrolysis

-

XFree inhibitor in medium is not actively taken up

Background and principles of Inhibigens

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• XLD • Brilliance Salmonella (InhibigenTM)

Why use Inhibigens?

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Why use Inhibigens?

• Reduce stress on target organism

• Improve sensitivity

• Reduce growth of non-target organisms

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Current Inhibigen Situation

• Inhibigens are a patented concept• Small scale manufacture • Currently only one product containing Inhibigen compounds

• Many more are in the pipeline