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Updated: Aug 17, 2026
A High-throughput Platform for the Screening of Salmonella spp./Shigella spp.
Published on: November 7, 2018
Exploring the use of Congo red agar in improving the serotyping of non-serotypeable Shigella with In-silico evidence
Ronit Juthani1, Ankita Das2, Kamali Doss2
1Jawaharlal Institute of Postgraduate Medical Institute and Research (JIPMER), Puducherry, India.
Objectives:
To assess if congo red could make non-serotypeable Shigella strains serotypeable and to employ molecular docking to determine the basis of the same phenomenon.
Methods:
We used 42 bacterial strains of non-serotypeable Shigella collected from 2012 to 2019 for this study. Each bacterial strain was freshly inoculated onto congo red agar and incubated at 37° C for 18-24 h. Bacterial colonies obtained were re-subjected to biochemical tests followed by serotyping and serogrouping. In-silico studies to investigate the interaction between MxiC protein of T3SS and O-antigen LPS with congo red were performed.
Results:
Of the total 42 non-serotypeable Shigella studied, (26/42)62% were capable of being serotyped following the use of congo red agar, 65% were Shigella flexneri, 19% were Shigella dysenteriae, while 2 strains (7%) each of Shigella boydii and Shigella sonnei were detected. We observed no change in their biochemical properties. The in-silico molecular docking studies revealed high binding affinity between congo red and the B-Chain of Mxi C. Out of the 5 chains of the O-Antigen, congo red showed robust binding with the B-chain with the involvement of a cluster of hydrophobic interactions between them. This may have a crucial role in the conversion of non-serotypeable strains to serotypeable strains on exposure to congo red as observed in our study.
Conclusion:
Congo red agar as a medium converts a sizeable percentage of non-serotypeable Shigella strains to serotypeable Shigella strains.
