Biofilm is a gel-like layer produced by several microorganisms that consisted of exopolysaccharide (EPS), DNA, water, protein, and other polysaccharides, and is formed by attaching to any living or non-living surfaces. In addition, being one of the main causes of various infections that affect human health, biofilm is also responsible for the remarkable problems in food, agriculture, livestock industries, and irrigation and ventilation systems. Therefore, in order to take precautions against the damages, the detection of the biofilm formation is very crucial.

There are different types of methods for detecting the in vitro biofilm formation. One of them is the congo red agar (CRA) method. In this method, a biofilm producing microorganism, changes the colour of the medium into bright black from red-pink.

In this study, it was aimed to determine the biofilm production of 21 clinically isolated multidrug resistant strains, namely 11 Escherichia coli strains, Acinetobacter baumannii, Candida albicans, Candida glabrata, Candida tropicalis, Klebsiella pneumoniae, Providencia rustigianii, Serratia odorifera, Shigella flexneri, Staphylococcus aureus MRSA and Streptococcus pneumoniae by using the CRA method. According to the results, it was determined that 10 of the existing strains (K. pneumoniae, S. aureus MRSA, C. albicans and 7 E. coli strains) produced biofilm.