Biofilm Formation by Staphylococcus epidermidis Depends on Functional RsbU, an Activator of the sigB Operon: Differential Activation Mechanisms Due to Ethanol and Salt Stress

Abstract

Staphylococcus epidermidis is a common pathogen in medical device-associated infections. Its major pathogenetic factor is the ability to form adherent biofilms. The polysaccharide intercellular adhesin (PIA), which is synthesized by the products of the icaADBC gene cluster, is essential for biofilm accumulation. In the present study, we characterized the gene locus inactivated by Tn917 insertions of two isogenic, icaADBC-independent, biofilm-negative mutants, M15 and M19, of the biofilm-producing bacterium S. epidermidis 1457. The insertion site was the same in both of the mutants and was located in the first gene, rsbU, of an operon highly homologous to the sigB operons of Staphylococcus aureus and Bacillus subtilis. Supplementation of Trypticase soy broth with NaCl (TSB NaCl ) or ethanol (TSB EtOH ), both of which are known activators of sigB, led to increased biofilm formation and PIA synthesis by S. epidermidis 1457. Insertion of Tn917 into rsbU, a positive regulator of alternative sigma factor B , led to a biofilm-negative phenotype and almost undetectable PIA production. Interestingly, in TSB EtOH , the mutants were enabled to form a biofilm again with phenotypes similar to those of the wild type. In TSB NaCl , the mutants still displayed a biofilm-negative phenotype. No difference in primary attachment between the mutants and the wild type was observed. Similar phenotypic changes were observed after transfer of the Tn917 insertion of mutant M15 to the independent and biofilm-producing strain S. epidermidis 8400. In 11 clinical S. epidermidis strains, a restriction fragment length polymorphism of the sigB operon was detected which was independent of the presence of the icaADBC locus and a biofilm-positive phenotype. Obviously, different mechanisms are operative in the regulation of PIA expression in stationary phase and under stress induced by salt or ethanol.Staphylococcus epidermidis, a normal inhabitant of human skin and mucous membranes, is the predominant cause of foreign-body-associated infections (43). In addition, S. epidermidis is isolated with increasing frequency as the causative pathogen of nosocomial sepsis and other nosocomial infections, ranking among the five most frequent nosocomial pathogens (43, 49). The pathogenesis of S. epidermidis infections is correlated with the ability to form biofilms on polymer surfaces (5, 58).Biofilm formation proceeds in two phases (23,24). Primary attachment of bacterial cells to a polymer surface is a complex process influenced by a variety of factors, including hydrophobic interactions, presence of host proteins, and specific bacterial proteins and polysaccharides like the capsular polysaccharide adhesin, the autolysin AtlE, and other staphylococcal surface proteins (15,17,33,38,39,50,51). This is followed by the second phase leading to accumulation of bacteria in a multilayered biofilm embedded in an amorphous glycocalyx. Synthesis of the polysaccharide intercellular adhesin (PIA) is essential for bacterial cell accumulation because it mediates cell-to-ce...

The role of σ B in persistence of Staphylococcus epidermidis foreign body infection

“…This is consistent with earlier data (Knobloch et al, 2001;Mack et al, 2000). Data from in vitro experiments (Jager et al, 2005) suggest that PIA is necessary for biofilm stability.…”

Hydrogen peroxide induced repression of icaADBC transcription and biofilm development in Staphylococcus epidermidis

“…20 Interestingly, in contrast to our findings in S. epidermidis, H 2 O 2 -mediated repression of the ica locus in S. aureus was not associated with changes in icaR transcription. 19 Regulation of icaR expression and biofilm development in S. epidermidis appears to involve at least two regulatory pathways, the first of which is dependent on the alternative stress-responsive sigma factor s B , 21,22 and a second s B -independent signaling pathway triggered by ethanol. 10 In S. epidermidis, stress-induced activation of s B indirectly leads to repression of the icaR gene and activation of the icaADBC operon.…”

Staphylococcal Biofilms

“…In S. aureus or in S. epidermidis, several global regulators have been shown to regulate ica transcription or PIA expression: the DNA-binding protein SarA and the alternative sigma factor SigB up-regulate whereas the quorum-sensing system luxS down-regulates (Knobloch et al 2001;Tormo et al 2005;Xu et al 2006). In contrast, agr does not regulate PIA expression Vuong et al 2003).…”