Detection of the intercellular adhesion gene cluster (ica) and phase variation in Staphylococcus epidermidis blood culture strains and mucosal isolates

Abstract

Staphylococcus epidermidis is a common cause of catheter-associated infections and septicemia in immunocompromised patients. To answer the question whether S. epidermidis skin isolates differ from isolates causing septicemic diseases, 51 strains obtained from blood cultures, 1 strain from shunt-associated meningitis, and 36 saprophytic isolates were characterized. The study demonstrates that most of the blood culture strains formed a multilayered biofilm on plastic material, whereas skin and mucosal isolates did not. Moreover, biofilm-producing strains were found to generate large bacterial autoaggregates in liquid culture. Autoaggregation and biofilm formation on polymer surfaces was associated with the presence of a DNA sequence encoding an intercellular adhesion gene cluster (ica) that mediates the production of a polysaccharide 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 adhesin-negative strains formed red colonies. Upon subcultivation on Congo red agar, the black colony forms of the blood culture strains exhibited red colony variants which were biofilm and autoaggregation negative and occurred at a frequency of 10 ؊5. The DNA analysis of these S. epidermidis variants by pulsed-field gel electrophoresis and Southern hybridization with an ica-specific gene probe revealed no detectable difference between the black and red colony types. Moreover, after repeated passage, the phenotype of the parent strain could be restored. Therefore, these colony forms were regarded as phase variants. This phenotypic change was observed exclusively in adhesin-positive clinical isolates and not in adhesin-negative saprophytic strains of S. epidermidis.

Assessment of ica operon carriage and biofilm production in Staphylococcus epidermidis isolates causing bacteraemia in bone marrow transplant recipients

“…Several studies have attempted to evaluate the role of biofilm production in virulence, but the results have been somewhat contradictory [17][18][19][20]. However, recent clinical studies have suggested that PIA is important for biofilm accumulation, and that the presence of the icaADBC operon coding for PIA is related to the clinical significance of S. epidermidis isolates [4][5][6][7][8][21][22][23]. In the present study, biofilm production was associated with a shorter interval between catheter insertion and the onset of bacteraemia, suggesting that biofilm-producing strains colonise catheters more rapidly than non-producers.…”

“…Production of PIA is certainly subjected to on-off switching, and may be involved in S. epidermidis phase-variation that might improve bacterial survival and growth under changing environmental conditions in vivo [25]. Environmental regulation may play an important role in biomaterial-related disease [8,22,23,[26][27][28][29][30][31].…”

icaand beyond: biofilm mechanisms and regulation inStaphylococcus epidermidisandStaphylococcus aureus

“…In S. epidermidis, the ica gene cluster appears to have an important role in the pathogenesis of device-related infections. For instance, Ziebuhr et al (1999) reported that c. 85% of S. epidermidis blood culture isolates contained the ica genes compared with 6% of saprophytic isolates, while a number of other studies have indicated that the ica locus may be a significant marker discriminating between significant and contaminating isolates (Frebourg et al, 2000;Galdbart et al, 2000;Fitzpatrick et al, 2002;Rohde et al, 2004;Li et al, 2005). Recent in vitro studies have provided evidence that PIA/PNAG is also required for immune evasion and virulence in S. epidermidis (Vuong et al, 2004).…”

A comparative analysis of phenotypic and genotypic methods for the determination of the biofilm-forming abilities of Staphylococcus epidermidis

“…Several studies have been undertaken in order to determine the genetic and/or the environmental factors responsible for in vitro biofilm formation by S. epidermidis, the leading opportunistic pathogen involved in infections associated with biomaterials. A number of reports (Ziebuhr et al, 1997;Galdbart et al, 2000;McKenney et al, 2000;Mack et al, 2004Mack et al, , 2007Maira-Litran et al, 2004;Rohde et al, 2005;Stevens et al, 2008) have highlighted that the ica and aap genes, known determinants of polysaccharide-and protein-mediated biofilm production, are widespread among clinically significant S. epidermidis isolates. Therefore, polysaccharide intercellular adhesin, also called the slime exopolysaccharide component, and accumulationassociated protein have been described as factors playing an essential role in biofilm formation (Cramton et al, 1999;Mack, 1999;O'Gara & Humphreys, 2001;Götz, 2002).…”