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. 1977 Oct;18(1):94–98. doi: 10.1128/iai.18.1.94-98.1977

Detection and differentiation of iron-responsive avirulent mutants on Congo red agar.

S M Payne, R A Finkelstein
PMCID: PMC421198  PMID: 409688

Abstract

Agar medium containing Congo red dye differentiates virulent and avirulent colonies of Shigella, Vibrio cholerae, Escherichia coli, and Neisseria meningitidis. Like virulent plague bacilli, wild-type cells of these species absorb the dye and produce red colonies. Mutants or colonial variants have been isolated that fail to absorb the dye and produce colorless colonies. These mutants exhibit reduced virulence in the chicken embryo model, but their virulence is enhanced by supplementation with iron. Of those species tested, only Neisseria gonorrhoeae isolates failed to grow in the presence of this dye. Inhibition of growth by Congo red may thus provide a simple means for differentiating gonococci from other Neisseria.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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