OBJECTIVES: Biofilm formation is one of the important features of Staphylococcus 
epidermidis, particularly in nosocomial infections. We aimed to investigate the 
biofilm production by phenotypic methods and the presence of ica genes in S 
epidermidis.
METHODS: A total of 41 S epidermidis isolates were recovered from different 
clinical specimens. Biofilm formation was evaluated by microtiter plate, tube 
method and Congo red agar method. The presence of icaA and icaD genes was 
investigated by PCR. Validity of methods (sensitivity and specificity), and 
metrics for test performance (positive/negative predictive value, and 
positive/negative likelihood ratio) were determined.
RESULTS: By both microtiter plate and tube method, 53.6% of S epidermidis 
isolates were able to produce biofilm, whilst only 24.4% of isolates provided a 
biofilm phenotype on Congo red agar plates. icaA and icaD genes were found in 
100% and 95.1% of isolates, respectively. Biofilm phenotypes accounted for 4.8% 
by microtiter plate assay, despite the absence of the ica gene. Congo red agar 
and PCR exhibited a lower sensitivity (18% and 45.5%, respectively) for 
identifying the biofilm phenotype in comparison to microtiter plate.
CONCLUSION: The microtiter plate method remains generally a better tool to 
screen biofilm production in S epidermidis. In addition, the ability of S 
epidermidis to form biofilm is not always dependent on the presence of ica 
genes, highlighting the importance of ica-independent mechanisms of biofilm 
formation. The use of reliable methods to specifically detect biofilms can be 
helpful to treat the patients affected by such problematic bacteria.