Congo Red Agar (CRA) Test for Biofilm Assay

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Bacteria tend to live in a community called a biofilm. A biofilm detection/measurement technique is called biotechnology if the technique targets specific biological properties of the microorganisms of which the biofilm is composed. Congo Red Agar (CRA) is used as a new alternative method for detecting slime production by coagulase-negative staphylococci and is more reliable than the Christensen method. CRA has been used in the past to detect biofilm production by S. epidermidis, and this approach correlates well with a biofilm-positive phenotype observed in vitro. The results are usually based on the colony color produced, which ranges from red for non-biofilm-producing strains to black for biofilm-producing strains.

CRA Test at Creative Biolabs

The CRA test developed is based on the subculture of the bacterial strains on brain heart infusion agar (BHIA), supplemented with sucrose and Congo red dye. This agar allowed colonies to differentiate in two colors, with black indicating strong biofilm production and red indicating no biofilm production. This is a quantitative test because it is based on a subjective chromatic evaluation.

Biofilm formation test for CRA and MCRA methods.Fig.1 Biofilm formation test for CRA and MCRA methods. (Normanita, 2020)


The accuracy of the method can be improved by adding or replacing some substances or modifying some parameters.

  • Fast
  • Easy
  • Sensitive
  • Cheap
  • Reproducible
  • The colonies remain viable in the medium for further analysis.

Creative Biolabs provides a full range of high-quality next-generation probiotics research services. By using state-of-the-art equipment and an experienced team of experts using the latest technologies, we have supported a wide variety of projects for multiple scientists worldwide. With a limited lead time, we plan the project properly to help you achieve better results while saving you money. If you are interested in our CRA test, please do not hesitate to contact us.


  1. Normanita, R. Validity Of Congo Red Agar And Modified Congo Red Agar To Detect Biofilm Of Enterococcus Faecalis. Saintika Medika. 2020, 16(1): 55-65.

For Research Use Only. Not intended for use in food manufacturing or medical procedures (diagnostics or therapeutics). Do Not Use in Humans.

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For Research Use Only. Not intended for use in food manufacturing or medical procedures (diagnostics or therapeutics). Do Not Use in Humans.

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