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Journal of Bacteriology, April 2001, p. 2624-2633, Vol. 183, No. 8
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.8.2624-2633.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

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

Johannes K.-M. Knobloch,* Katrin Bartscht, Axel Sabottke, Holger Rohde, Heinz-Hubert Feucht, and Dietrich Mack

Institut für Medizinische Mikrobiologie und Immunologie, Universitätsklinikum Hamburg-Eppendorf, D-20246 Hamburg, Germany

Received 5 September 2000/Accepted 4 January 2001

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 (TSBNaCl) or ethanol (TSBEtOH), 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 sigma B, led to a biofilm-negative phenotype and almost undetectable PIA production. Interestingly, in TSBEtOH, the mutants were enabled to form a biofilm again with phenotypes similar to those of the wild type. In TSBNaCl, 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.

* Corresponding author. Mailing address: Institut für Medizinische Mikrobiologie und Immunologie, Universitätsklinikum Hamburg- Eppendorf, Martinistr. 52, D-20246 Hamburg, Germany. Phone: 49 40 42803 3147. Fax: 49 40 42803 4881. E-mail: knobloch{at}uke.uni-hamburg.de.

Journal of Bacteriology, April 2001, p. 2624-2633, Vol. 183, No. 8
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.8.2624-2633.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.