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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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?
• 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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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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Why use Inhibigens?
• Reduce stress on target organism
• Improve sensitivity
• Reduce growth of non-target organisms
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