Summary: Because of its biofilm forming potential Staphylococcus epidermidis has evolved as a leading cause of device‐related infections. The polysaccharide intercellular adhesin (PIA) is significantly involved in biofilm accumulation. However, infections because of PIA‐negative strains are not uncommon, suggesting the existence of PIA‐independent biofilm accumulation mechanisms. Here we found that biofilm formation in the clinically significant S. epidermidis 5179 depended on the expression of a truncated 140 kDa isoform of the 220 kDa accumulation‐associated protein Aap. As expression of the truncated Aap isoform leads to biofilm formation in aap‐negative S. epidermidis 1585, this domain mediates intercellular adhesion in a polysaccharide‐independent manner. In contrast, expression of full‐length Aap did not lead to a biofilm‐positive phenotype. Obviously, to gain adhesive function, full‐length Aap has to be proteolytically processed through staphylococcal proteases as demonstrated by inhibition of biofilm formation by α₂‐macroglobulin. Importantly, also exogenously added granulocyte proteases activated Aap, thereby inducing biofilm formation in S. epidermidis 5179 and four additional, independent clinical S. epidermidis strains. It is therefore reasonable to assume that in vivo effector mechanisms of the innate immunity can directly induce protein‐dependent S. epidermidis cell aggregation and biofilm formation, thereby enabling the pathogen to evade clearance by phagocytes.

The outbreak of Shiga-toxigenic Escherichia coli (STEC), which struck Germany in May-June 2011, illustrated the effects of a bacterial epidemic on a wealthy, modern, industrialized society, with more than 3000 cases and more than 50 deaths.¹ During an outbreak, rapid and accurate pathogen identification and characterization is essential for the management of individual cases and of an entire outbreak. Traditionally, clinical bacteriology has relied primarily on laboratory isolation of bacteria in pure culture as a prerequisite to identification and characterization of an outbreak strain. Often, however, in vitro culture proves slow, difficult, or even impossible, and recognition of an outbreak strain can be difficult if it does not belong to a known variety or species for which specific laboratory tests and diagnostic criteria already exist. For example, during the German outbreak, infection was caused by an unusual serotype (STEC O104:H4) that had not previously been seen in the context of epidemic disease and could not be detected easily with the standard microbiological methods in use at the start of the outbreak for diagnosing STEC infection.

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.

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.

Early and adequate antimicrobial therapy has been shown to improve the clinical outcome in bloodstream infections (BSI). To provide rapid pathogen identification for targeted treatment, we applied matrix-assisted laser desorption-ionization time of flight (MALDI-TOF) mass spectrometry fingerprinting to bacteria directly recovered from blood culture bottles. A total of 304 aerobic and anaerobic blood cultures, reported positive by a Bactec 9240 system, were subjected in parallel to differential centrifugation with subsequent mass spectrometry fingerprinting and reference identification using established microbiological methods. A representative spectrum of bloodstream pathogens was recovered from 277 samples that grew a single bacterial isolate. Species identification by direct mass spectrometry fingerprinting matched reference identification in 95% of these samples and worked equally well for aerobic and anaerobic culture bottles. Application of commonly used score cutoffs to classify the fingerprinting results led to an identification rate of 87%. Mismatching mostly resulted from insufficient bacterial numbers and preferentially occurred with Gram-positive samples. The respective spectra showed low concordance to database references and were effectively rejected by score thresholds. Spiking experiments and examination of the respective study samples even suggested applicability of the method to mixed cultures. With turnaround times around 100 min, the approach allowed for reliable pathogen identification at the day of blood culture positivity, providing treatment-relevant information within the critical phase of septic illness.