Staphylococcus epidermidis is a frequent pathogen in infections associated with 
orthopedic implants. We studied 123 S. epidermidis strains from infections 
related to orthopedic implants, as regards their ability to express a factor of 
virulence, namely the slime, an extracellular polysaccharide, which mediates 
adherence to implants and bacterial colonization. The slime-producing ability 
was determined by PCR detection of icaA and icaD genes responsible for slime 
synthesis, and by culture on Congo red agar plates in which slime-producing 
strains form black colonies, while nonslime-forming ones develop red colonies. 
56% of the S. epidermidis isolates were icaA- icaD-positive and grew to become 
black colonies. In the evaluation of the distribution of slime-forming strains 
in different sites and types of implants, we found a slight, but not 
statistically significant, increase in slime-forming strains in total joint 
prostheses, where tissue compression near the articular faces can form niches in 
which bacteria crowd, sheltered by the slime. Our findings confirm the role of 
ica genes as a virulence marker in the pathogenesis of implant-associated 
orthopedic infections. However, they do not show the existence of a higher 
frequency of slime-positive strains in a specific type of implant.