DETECTION OF THE INTERCELLULAR-ADHESION GENE-CLUSTER (ICA) AND PHASE VARIATION IN STAPHYLOCOCCUS-EPIDERMIDIS BLOOD CULTURE STRAINS AND MUCOSAL ISOLATES

Staphylococcus epidermidis is a common cause of catheter-associated in fections and septicemia in immuno-compromised patients, To answer the question whether S. epidermidis skin isolates differ from isolates cau sing septicemic diseases, 51 strains obtained from blood cultures, 1 s train from shunt-associated meningitis, and 36 saprophytic isolates we re characterized, The study demonstrates that most of the blood cultur e strains formed a multilayered biofilm on plastic material, whereas s kin and mucosal isolates did not, Moreover, biofilm-producing strains were found to generate large bacterial autoaggregates in liquid cultur e, Autoaggregation and biofilm formation on polymer surfaces was assoc iated with the presence of a DNA sequence encoding an intercellular ad hesion gene cluster (ica) that mediates the production of a polysaccha ride intercellular adhesin, The presence of the intercellular adhesion genes in blood culture isolates was also found to be correlated with the exhibition of black colonies on Congo red agar, whereas the adhesi n-negative strains formed red colonies, Upon subcultivation on Congo r ed agar, the black colony forms of the blood culture strains exhibited red colony variants which were biofilm and autoaggregation negative a nd occurred at a frequency of 10(-5). The DNA analysis of these S. epi dermidis variants by pulsed-field gel electrophoresis and Southern hyb ridization with an ica-specific gene probe revealed no detectable diff erence between the black and red colony types, Moreover, after repeate d passage, the phenotype of the parent strain could be restored, There fore, these colony forms were regarded as phase variants. This phenoty pic change was observed exclusively in adhesin-positive clinical isola tes and not in adhesin-negative saprophytic strains of S. epidermidis.