Biofilms are composed of bacterial cells embedded in an extracellular polysaccharide matrix. A major component of the Escherichia coli biofilm matrix is PGA, a linear polymer of N -acetyl- d -glucosamine residues in β(1,6) linkage. PGA mediates intercellular adhesion and attachment of cells to abiotic surfaces. In this report, we present genetic and biochemical evidence that PGA is also a major matrix component of biofilms produced by the human periodontopathogen Actinobacillus actinomycetemcomitans and the porcine respiratory pathogen Actinobacillus pleuropneumoniae . We also show that PGA is a substrate for dispersin B, a biofilm-releasing glycosyl hydrolase produced by A. actinomycetemcomitans , and that an orthologous dispersin B enzyme is produced by A. pleuropneumoniae . We further show that A. actinomycetemcomitans PGA cross-reacts with antiserum raised against polysaccharide intercellular adhesin, a staphylococcal biofilm matrix polysaccharide that is genetically and structurally related to PGA. Our findings confirm that PGA functions as a biofilm matrix polysaccharide in phylogenetically diverse bacterial species and suggest that PGA may play a role in intercellular adhesion and cellular detachment and dispersal in A. actinomycetemcomitans and A. pleuropneumoniae biofilms.

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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 Tn 917 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 Tn 917 into rsbU , a positive regulator of alternative sigma factor ς ^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 Tn 917 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.

Medical device-associated infections, most frequently caused by coagulase-negative staphylococci, especially Staphylococcus epidermidis, are of increasing importance in modern medicine. Regularly, antimicrobial therapy fails without removal of the implanted device. The most important factor in the pathogenesis of medical device-associated staphylococcal infections is the formation of adherent, multilayered bacterial biofilms. There is urgent need for an increased understanding of the functional factors involved in biofilm formation, the regulation of their expression, and the interaction of those potential virulence factors in device related infection with the host. Significant progress has been made in recent years which may ultimately lead to new rational approaches for better preventive, therapeutic, and diagnostic measures.