Advances in culture media design
(Chromogen and Inhibigen compounds)
Neal Parker
Industrial account manager
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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Background and principles of chromogenic media
Chromogen
Sugar component
(e.g. galactose)
Chromophore component (e.g. indoxyl derivative
such as 5-bromo-4-chloro-3-indoxyl)
Uptake
E. coli
Enzyme
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Background and principles of chromogenic media
E. coli
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Background and principles of chromogenic media
Br
Br
OHOH
Cl
H O
H
HO
H
H
Cl
-galactosidase
oxidation
O
O
NH
OH
H
5-bromo-4-chloro-3-indoxyl--Dgalactopyranoside (X-Gal)
NH
HN
O
OHOH
H O
H
HO
H
OH
OH
Br
H
H
galactose
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Cl
blue-turquoise chromophore
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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Background and principles of Inhibigens
InhibigenTM
Sugar or
amino acid
component
Inhibitor
component
(AEP)
Uptake
X
Free inhibitor in
medium is not
actively taken up
Inhibition of cell
wall synthesis
Specific enzyme hydrolysis
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Loss of
viability
Why use Inhibigens?
• XLD
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• Brilliance Salmonella
(InhibigenTM)
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
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