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

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.

Congo red inhibition as a convenient diagnostic for Flavobacterium psychrophilum

“…The selective inhibitory effect of congo red within a bacterial genus, as described here, has also been observed among Neisseria (Payne & Finkelstein 1977) and Porphyromonas spp. (Mayrand, Bourgeau, Grenier & Lacroix 1984).…”

“…(Mayrand, Bourgeau, Grenier & Lacroix 1984). Payne & Finkelstein (1977) reported that unlike other Neisseria spp. tested, N. gonorrhoeae failed to grow in the presence of congo red.…”

Culture media for the differentiation of isolates of Yersinia ruckeri, based on detection of a virulence factor

“…Differentiation between pathogenic and non-pathogenic strains of bacteria using bacteriological media containing dyes such as Congo red and Coomassie blue has been described for a number of species of Gram-negative bacteria, including Neisseria meningitidis, Vibrio cholerae and Escherichia coli (Payne and Finkelstein 1977), Shigella flexneri (Maurelli et al 1984) and Aeromonas salmonicida (Ishiguro et al 1985). Of special interest is the use of dyes for differentiation of strains of Y .…”

Epidemiology of diarrhoea caused by rotavirus and Escherichia coli in lambs in Kashmir valley, India

“…Pathogenic strains of E. coli are known to produce several virulence factors that can be demonstrated by different in vitro and in vivo methods under laboratory conditions. The ability to bind congo red (CR) dye in agar medium has been proposed as a marker for the invasive ability of several enteropathogens including E. coli (Payne and Finkelstein, 1977;Berkhoff and Vinal, 1986). Yoder et al (1989) provided evidence that CR binding might be directly related to virulence.…”