A 140-kilodalton extracellular protein is essential for the accumulation of Staphylococcus epidermidis strains on surfaces

Role of surface protein SasG in biofilm formation by Staphylococcus aureus

The SasG surface protein of Staphylococcus aureus has been shown to promote the formation of biofilm. SasG comprises an N-terminal A domain and repeated B domains. Here we demonstrate that SasG is involved in the accumulation phase of biofilm, a process that requires a physiological concentration of Zn(2+). The B domains, but not the A domain, are required. Purified recombinant B domain protein can form dimers in vitro in a Zn(2+)-dependent fashion. Furthermore, the protein can bind to cells that have B domains anchored to their surface and block biofilm formation. The full-length SasG protein exposed on the cell surface is processed within the B domains to a limited degree, resulting in cleaved proteins of various lengths being released into the supernatant. Some of the released molecules associate with the surface-exposed B domains that remain attached to the cell. Studies using inhibitors and mutants failed to identify any protease that could cause the observed cleavage within the B domains. Extensively purified recombinant B domain protein is very labile, and we propose that cleavage occurs spontaneously at labile peptide bonds and that this is necessary for biofilm formation.

Understanding the significance of Staphylococcus epidermidis bacteremia in babies and children

PURPOSE OF REVIEW

This article provides an overview of Staphylococcus epidermidis bacteremia/sepsis and coagulase-negative staphylococci (CoNS) infections in neonates and children.

RECENT FINDINGS

The incidence of S. epidermidis and CoNS sepsis in neonates is still very high and preventing and treating disease remains difficult. There has been recent progress in understanding the pathogenesis of S. epidermidis infection, interaction of S. epidermidis with host defenses, and risk factors for the development of S. epidermidis disease. For example, we have gained more insight into the development of biofilm-associated catheter infections, which are responsible for recurrent CoNS infections in hospitalized premature neonates and are especially difficult to treat owing to intrinsic resistance of biofilms to antibiotics.

SUMMARY

Biofilm-associated catheter infections by S. epidermidis occur frequently in neonates and adults. S. epidermidis bloodstream infections are particularly problematic in neonates. Prophylaxis in the form of eradicating colonizing S. epidermidis may be a double-edged sword, as S. epidermidis colonization may be beneficial to the host. New drugs may arise from a better understanding of S. epidermidis virulence and analysis of risk factors may help identify neonates susceptible to bacterial sepsis. However, reducing morbidity should always begin by increasing hygiene in hospital settings to reduce the introduction of potentially harmful opportunistic pathogens such as S. epidermidis on indwelling medical devices or during surgery.

Nitazoxanide inhibits biofilm formation by Staphylococcus epidermidis by blocking accumulation on surfaces

Coagulase-negative species of Staphylococcus are often associated with opportunistic hospital-acquired infections that arise from the colonization of indwelling catheters. Here we show that the antiparasitic drug nitazoxanide (NTZ) and its active metabolite, tizoxanide (TIZ), are inhibitory to the growth of Staphylococcus epidermidis and other staphylococci, including methicillin-resistant Staphylococcus aureus strains, under aerobic and microaerobic conditions (MICs, 8 to 16 microg/ml). At sub-MIC levels, NTZ and TIZ also inhibited biofilm production under static conditions by strains of S. epidermidis and Staphylococcus haemolyticus with a 50% inhibitory concentration of approximately 2.5 microg/ml (8 microM). The 5-nitro group was required for biological activity, and a hydrophilic derivative of NTZ (AMIX) also inhibited biofilm formation. NTZ did not disperse the existing biofilm but did block further accumulation. Sub-MICs of NTZ had no effect on primary attachment to surfaces at either 4 or 37 degrees C. The inhibitory action of NTZ and TIZ, but not vancomycin, on biofilm production could be reversed by the addition of zinc salts (2.5 to 40 microM) but not other metals, suggesting that NTZ might target the zinc-dependent accumulation-associated protein (Aap) that mediates accumulation on surfaces. However, neither NTZ nor TIZ formed chelation complexes with zinc salts, based on spectrophotometric and nuclear magnetic resonance analyses, and addition of excess zinc to NTZ-grown bacteria (apo-Aap) did not restore the accumulation phenotype. Our studies suggest that sub-MIC levels of NTZ may affect the assembly or function of cell structures associated with the biofilm phenotype.

Staphylococcus colonization of the skin and antimicrobial peptides

Staphylococci are the most abundant skin-colonizing bacteria and the most important causes of nosocomial infections and community-associated skin infections. Molecular determinants of staphylococcal skin colonization include surface polymers and proteins that promote adhesion and aggregation, and a wide variety of mechanisms to evade acquired and innate host defenses. Antimicrobial peptides (AMPs) likely play a central role in providing immunity to bacterial colonization on human epithelia. Recent research has shown that staphylococci have a broad arsenal to combat AMP activity, and can regulate expression of AMP-resistance mechanisms depending on the presence of AMPs. While direct in vivo evidence is still lacking, this suggests that the interplay between AMPs and AMP resistance mechanisms during evolution had a crucial role in rendering staphylococci efficient colonizers of human skin.

Staphylococcus epidermidis device-related infections: pathogenesis and clinical management

Staphylococcus epidermidis, the most frequently isolated coagulase-negative staphylococcus, is the leading cause of infection related to implanted medical devices (IMDs). This is directly related to its capability to establish multilayered, highly structured biofilms on artificial surfaces. At present, conventional systemic therapies using standard antimicrobial agents represent the main strategy to treat and prevent medical device-associated infections. However, device-related infections are notoriously difficult to treat and bacteria within biofilm communities on the surface of IMDs frequently outlive treatment, and removal of the medical device is often required for successful therapy. Importantly, major advances in this research area have been made, leading to a greater understanding of the complexities of biofilm formation of S. epidermidis and resulting in significant developments in the treatment and prevention of infections related to this member of the coagulase-negative group of staphylococci. This review will examine the pathogenesis of the clinically significant S. epidermidis and provide an overview of the conventional and emerging antibiofilm approaches in the management of medical device-associated infections related to this important nosocomial pathogen.

Structure, function and contribution of polysaccharide intercellular adhesin (PIA) to Staphylococcus epidermidis biofilm formation and pathogenesis of biomaterial-associated infections

Staphylococcus epidermidis is of major importance in infections associated with indwelling medical devices. The tight pathogenic association is essentially linked to the species ability to form adherent biofilms on artificial surfaces. Aiming at identifying novel targets for vaccination or therapy much effort has been made to unravel the molecular mechanisms leading to S. epidermidis biofilm formation. At present, polysaccharide intercellular adhesin (PIA) is the best studied factor involved in S. epidermidis biofilm accumulation. PIA is a glycan of beta-1,6-linked 2-acetamido-2-deoxy-D-glucopyranosyl residues of which 15 % are non-N-acetylated. PIA-producing S. epidermidis are widespread in clinical strain collections and PIA synthesis has been shown to be essential for S. epidermidis virulence. Moreover, PIA homologues have been identified in many other staphylococcal species, including the major human pathogen Staphylococcus aureus, and also Gram-negative human pathogens, suggesting that it might represent a more general pathogenicity principle in biofilm-related infections. In this review the current knowledge about the structure and biosynthesis of PIA is summarized. Additionally, information on its role in pathogenesis of biomaterial-related and other type of infections and the potential use of PIA and related compounds for prevention of infection is discussed.

Molecular characterization of a novel Staphylococcus aureus surface protein (SasC) involved in cell aggregation and biofilm accumulation

Background

Staphylococci belong to the most important pathogens causing implant-associated infections. Colonization of the implanted medical devices by the formation of a three-dimensional structure made of bacteria and host material called biofilm is considered the most critical factor in these infections. To form a biofilm, bacteria first attach to the surface of the medical device, and then proliferate and accumulate into multilayered cell clusters. Biofilm accumulation may be mediated by polysaccharide and protein factors.

Methology/Principal Findings

The information on Staphylococcus aureus protein factors involved in biofilm accumulation is limited, therefore, we searched the S. aureus Col genome for LPXTG-motif containing potential surface proteins and chose the so far uncharacterized S. aureus surface protein C (SasC) for further investigation. The deduced SasC sequence consists of 2186 amino acids with a molecular mass of 238 kDa and has features typical of Gram-positive surface proteins, such as an N-terminal signal peptide, a C-terminal LPXTG cell wall anchorage motif, and a repeat region consisting of 17 repeats similar to the domain of unknown function 1542 (DUF1542). We heterologously expressed sasC in Staphylococcus carnosus, which led to the formation of huge cell aggregates indicative of intercellular adhesion and biofilm accumulation. To localize the domain conferring cell aggregation, we expressed two subclones of sasC encoding either the N-terminal domain including a motif that is found in various architectures (FIVAR) or 8 of the DUF1542 repeats. SasC or its N-terminal domain, but not the DUF1542 repeat region conferred production of huge cell aggregates, higher attachment to polystyrene, and enhanced biofilm formation to S. carnosus and S. aureus. SasC does not mediate binding to fibrinogen, thrombospondin-1, von Willebrand factor, or platelets as determined by flow cytometry.

Conclusions/Significance

Thus, SasC represents a novel S. aureus protein factor involved in cell aggregation and biofilm formation, which may play an important role in colonization during infection with this important pathogen.

Comparative subproteome analyses of planktonic and sessile Staphylococcus xylosus C2a: new insight in cell physiology of a coagulase-negative Staphylococcus in biofilm

Staphylococcus xylosus is a Gram-positive bacterium found on the skin of mammals and frequently isolated from food plants and fermented cheese or meat. To gain further insight in protein determinants involved in biofilm formation by this coagulase-negative Staphylococcus, a comparative proteomic analysis between planktonic and sessile cells was performed. With the use of a protocol previously developed, protein patterns of the cytoplasmic and cell envelope fractions were compared by 2-DE. Following protein identification by MALDI-TOF mass spectrometry and bioinformatic analyses, this study revealed differences in expression levels of 89 distinct proteins with 55 up-expressed and 34 down-expressed proteins in biofilm compared to planktonic cells. Most proteins differentially expressed were related to nitrogen and carbon metabolisms. Besides amino acid biosynthesis and protein translation, protein determinants related to protein secretion were up-expressed in biofilm, suggesting a more active protein trafficking in sessile cells. While up-expression of several enzymes involved in pentose phosphate and glycolytic pathways was observed in biofilm, connections with unexpected metabolic routes were further unravelled. Indeed, this proteomic analysis allowed identifying novel proteins that could be involved in a previously uncovered exopolysaccharide biosynthetic pathway in S. xylosus as well as several enzymes related to polyketide biosynthesis. This findings are particularly relevant considering exopolysaccharide production in S. xylosus is ica-independent contrary to coagulase-negative model strain Staphylococcus epidermidis RP62A.

The terminal A domain of the fibrillar accumulation-associated protein (Aap) of Staphylococcus epidermidis mediates adhesion to human corneocytes

The opportunistic pathogen Staphylococcus epidermidis colonizes indwelling medical devices by biofilm formation but is primarily a skin resident. In many S. epidermidis strains biofilm formation is mediated by a cell wall-anchored protein, the accumulation-associated protein (Aap). Here, we investigate the role of Aap in skin adhesion. Aap is an LPXTG protein with a domain architecture including a terminal A domain and a B-repeat region. S. epidermidis NCTC 11047 expresses Aap as localized, lateral tufts of fibrils on one subpopulation of cells (Fib(+)), whereas a second subpopulation does not express these fibrils of Aap (Fib(-)). Flow cytometry showed that 72% of NCTC 11047 cells expressed Aap and that 28% of cells did not. Aap is involved in the adhesion of Fib(+) cells to squamous epithelial cells from the hand (corneocytes), as the recombinant A-domain protein partially blocked binding to corneocytes. To confirm the role of the Aap A domain in corneocyte attachment, Aap was expressed on the surface of Lactococcus lactis MG1363 as sparsely distributed, peritrichous fibrils. The expression of Aap increased corneocyte adhesion 20-fold compared to L. lactis carrying Aap without an A domain. S. epidermidis isolates from catheters, artificial joints, skin, and the nose also used the A domain of Aap to adhere to corneocytes, emphasizing the role of Aap in skin adhesion. In addition, L. lactis expressing Aap with different numbers of B repeats revealed a positive correlation between the number of B repeats and adhesion to corneocytes, suggesting an additional function for the B region in enhancing A-domain-dependent attachment to skin. Therefore, in addition to its established role in biofilm formation, Aap can also promote adhesion to corneocytes and is likely to be an important adhesin in S. epidermidis skin colonization.

A comparison of Pseudomonas aeruginosa biofilm development on ZnSe and TiO2 using attenuated total reflection Fourier transform infrared spectroscopy

The growth of Pseudomonas aeruginosa PAO1 biofilms on ZnSe internal reflection elements (IREs) was compared with their growth on TiO(2)-coated ZnSe over several days using attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy. The effect of the TiO(2) coating on the IR spectra of reference compounds and cell suspensions was determined to aid in the interpretation of the data. The presence of TiO(2) on the surface of a ZnSe IRE tripled the size of the amide II peak and facilitated the detection of pyoverdin production due to its increased adsorption on the coated surface. A 50% increase in the length of the lag phase was observed for PAO1 growth on TiO(2)-coated surfaces as compared to growth on ZnSe. Biofilms on both surfaces exhibited a growth maximum for all components, followed by restructuring at the surface characterized by a decrease in the signal. The composition of biofilms grown on TiO(2) was relatively constant after the restructuring phase, while the extracellular polymeric substance (EPS) component of the biofilms grown on ZnSe gradually increased. The peak due to the carbohydrate component of EPS was much larger in the spectra of biofilms than in those of planktonic cells. The increase of the pyoverdin signal over time in the spectra of the biofilms on TiO(2) closely followed the overall increase in biomass. However, no signal from pyoverdin was detected in the presence of ferric ions.

Inhibition of Staphylococcus epidermidis biofilm formation by rabbit polyclonal antibodies against the SesC protein

Several well-studied proteins with defined roles in Staphylococcus epidermidis biofilm formation are LPXTG motif-containing proteins. Here, we investigate the possible use of the LPXTG motif-containing protein SesC (S. epidermidis surface protein C; accession no. NP_765787) as a target for antibodies to prevent biofilm formation. In vitro and in a in vivo rat model of catheter infection, gene and protein expression analysis showed that SesC is expressed more strongly in biofilm-associated cells than in planktonic cells and is expressed particularly during the late phase of in vivo biofilm formation. Polyclonal rabbit antibodies raised against SesC reduced the fibrinogen-binding ability of S. epidermidis RP62A and Staphylococcus aureus RN4220 transformants expressing SesC, inhibited in vitro biofilm formation by S. epidermidis strains 10b and 1457, and significantly reduced the numbers of bacteria in a 1-day-old in vivo biofilm (P < 0.001, one-way analysis of variance). Our findings revealed that SesC is a promising target for prevention and treatment of S. epidermidis biofilms because it affects both the primary attachment and biofilm accumulation phases. The precise role of SesC in biofilm formation remains to be identified.

The influence of antibodies on Staphylococcus epidermidis adherence to polyvinylpyrrolidone-coated silicone elastomer in experimental biomaterial-associated infection in mice

Biomaterial-associated infection (BAI) is a major problem in modern medicine, and is often caused by Staphylococcus epidermidis. We aimed to raise monoclonal antibodies (mAbs) against major surface protein antigens of S. epidermidis, and to assess their possible protective activity in experimental BAI. Mice were vaccinated with a cell wall protein preparation of S. epidermidis. A highly immunodominant antigen was identified as Accumulation-associated protein (Aap). mAbs against Aap and against surface-exposed lipoteichoic acid (LTA) were used for passive immunization of mice in experimental biomaterial-associated infection. Neither anti-Aap nor anti-LTA mAbs showed protection. Either with or without antibodies, tissue surrounding the implants was more often culture positive than the implants themselves, but bacterial adherence to the implants was significantly increased in mice injected with anti-LTA. In vitro, anti-Aap and anti-LTA did show binding to S. epidermidis, but no opsonic activity was observed. We conclude that antibodies against S. epidermidis LTA or Aap showed no opsonic activity and did not protect mice against BAI. Moreover, the increase in binding to implanted biomaterial suggests that passive immunization may increase the risk for BAI.

Staphylococcus epidermidis isolated from newborn infants express pilus-like structures and are inhibited by the cathelicidin-derived antimicrobial peptide LL37

Coagulase-negative staphylococci and its subtype Staphylococcus epidermidis are major indigenous Gram-positive inhabitants of the human skin. Colonization occurs in direct connection with birth and terrestrial adaptation. This study focuses on factors that may influence skin colonization of the newborn infant that relates to the immune status of both the bacteria and the host. Skin is an effective barrier against bacteria, and this function is partly mediated by the presence of antimicrobial peptides including human cathelicidin peptide LL37. Gram-positive bacteria have been described to have adhesive pili on their surface that mediates specific attachment to the host. Here, we identify, by negative staining transmission electron microscopy (EM), two different types of pilus-like structures commonly expressed on S. epidermidis isolated from newborn infants. We also show that the cathelicidin antimicrobial peptide LL37, constitutively expressed in the skin barrier of the newborn, significantly inhibited growth of S. epidermidis indicating its importance for the ecological stability of the skin microbiota. Further studies are required to elucidate molecular mechanisms of host-microbe interactions, both for the maintenance of a mutually beneficial homeostatic relationship and for the protection of self when it results in overt disease.

Staphylococcus epidermidis--the 'accidental' pathogen

Although nosocomial infections by Staphylococcus epidermidis have gained much attention, this skin-colonizing bacterium has apparently evolved not to cause disease, but to maintain the commonly benign relationship with its host. Accordingly, S. epidermidis does not produce aggressive virulence determinants. Rather, factors that normally sustain the commensal lifestyle of S. epidermidis seem to give rise to additional benefits during infection. Furthermore, we are beginning to comprehend the roles of S. epidermidis in balancing the epithelial microflora and serving as a reservoir of resistance genes. In this Review, I discuss the molecular basis of the commensal and infectious lifestyles of S. epidermidis.

Biofilm characteristics of Staphylococcus epidermidis isolates associated with device-related meningitis

Staphylococcus epidermidis biofilm causes device-related meningitis in neurosurgical patients. This study assessed the contribution of polysaccharide and protein to the development of a strong biofilm-positive phenotype in four S. epidermidis isolates associated with probable device-related meningitis, under varying environmental conditions. RT-PCR analysis of the intercellular adhesion operon (icaADBC) and assessment of polysaccharide intercellular adhesin (PIA) production indicated a correlation between increased icaA transcription and PIA production in ica(+) isolates grown in medium with 4 % ethanol and 4 % NaCl. Treatment of biofilm with sodium metaperiodate caused dispersion of adhered cells (P <0.0001), indicating involvement of PIA. Transcriptional levels of protein factors revealed that atlE transcription levels were similar in all isolates, whilst aap levels were variable, with induction being seen in two isolates following growth in the presence of alcohol or salt. Transcription of agr did not influence protein expression and RNAIII transcription varied among the strains. Although aap transcription was induced, the treatment of biofilm with proteinase K did not always disperse the biofilm. Our data suggest that, among the three ica(+) S. epidermidis isolates clinically associated with meningitis that were studied, PIA contributed to the strong biofilm-positive phenotype, whereas protein factors appeared to have a secondary role.

Biofilm formation by Staphylococcus haemolyticus

Infections due to coagulase-negative staphylococci (CoNS) most frequently occur after the implantation of medical devices and are attributed to the biofilm-forming potential of CoNS. Staphylococcus haemolyticus is the second most frequently isolated CoNS from patients with hospital-acquired infections. There is only limited knowledge of the nature of S. haemolyticus biofilms. The aim of this study was to characterize S. haemolyticus biofilm formation. We analyzed the biofilm-forming capacities of 72 clinical S. haemolyticus isolates. A detachment assay with NaIO(4), proteinase K, or DNase was used to determine the main biofilm components. Biofilm-associated genes, including the ica operon, were analyzed by PCR, and the gene products were sequenced. Confocal laser scanning microscopy (CLSM) was used to elucidate the biofilm structure. Fifty-three isolates (74%) produced biofilms after growth in Trypticase soy broth (TSB) with glucose, but only 22 (31%) produced biofilms after growth in TSB with NaCl. It was necessary to dissolve the biofilm in ethanol-acetone to measure the optical density of the full biofilm mass. DNase, proteinase K, and NaIO(4) caused biofilm detachment for 100%, 98%, and 38% of the isolates, respectively. icaRADBC and polysaccharide intercellular adhesin (PIA) production were found in only two isolates. CLSM indicated that the biofilm structure of S. haemolyticus clearly differs from that of S. epidermidis. We conclude that biofilm formation is a common phenotype in clinical S. haemolyticus isolates. In contrast to S. epidermidis, proteins and extracellular DNA are of functional relevance for biofilm accumulation, whereas PIA plays only a minor role. The induction of biofilm formation and determination of the biofilm mass also needed to be optimized for S. haemolyticus.

Novel staphylococcal cassette chromosome mec type, tentatively designated type VIII, harboring class A mec and type 4 ccr gene complexes in a Canadian epidemic strain of methicillin-resistant Staphylococcus aureus

Staphylococcal cassette chromosome mec (SCCmec) is a mobile genetic element characterized by flanking terminal direct and, in most cases, inverted repeat sequences, the mec and ccr gene complexes, and their surrounding DNA regions. Unique combinations of the mec and ccr gene complexes generate various SCCmec types. Six SCCmec types have been reported to date. We describe here a novel SCCmec type identified in a Canadian methicillin-resistant Staphylococcus aureus (MRSA) epidemic strain. MRSA clinical isolates were screened for known SCCmec types by multiplex and conventional PCR methods. Three phenotypically and genotypically identical MRSA clinical isolates with a pulsotype identical to CMRSA9 were identified locally and found to be nontypeable by available SCCmec typing schemes. Complete sequencing of the SCCmec element revealed a nucleotide fragment of 32,168 bp integrated at an identical chromosomal integration site (attBscc) at the 3' end of the orfX gene. The nucleotide sequences at the chromosome-SCCmec junction regions were typical of other SCCmec types, but the element harbored a unique combination of class A mec and type 4 ccr gene complexes. Sequence recombination analysis suggested that this unique SCCmec type may be derived from homologous recombination between the previously described SCC(RP62A) of S. epidermidis strain RP62A and SCC composite island of S. epidermidis ATCC 12228, respectively, or via recombination of other staphylococcal strains that carry the same or similar mobile cassettes. We identified a previously undescribed type of SCCmec from isolate C10682, tentatively designated type VIII, and we provide compelling evidence supporting the ability of SCC elements to transfer horizontally or undergo recombination to generate new SCCmec types.

A zinc-dependent adhesion module is responsible for intercellular adhesion in staphylococcal biofilms

Hospital-acquired bacterial infections are an increasingly important cause of morbidity and mortality worldwide. Staphylococcal species are responsible for the majority of hospital-acquired infections, which are often complicated by the ability of staphylococci to grow as biofilms. Biofilm formation by Staphylococcus epidermidis and Staphylococcus aureus requires cell-surface proteins (Aap and SasG) containing sequence repeats known as G5 domains; however, the precise role of these proteins in biofilm formation is unclear. We show here, using analytical ultracentrifugation (AUC) and circular dichroism (CD), that G5 domains from Aap are zinc (Zn(2+))-dependent adhesion modules analogous to mammalian cadherin domains. The G5 domain dimerizes in the presence of Zn(2+), incorporating 2-3 Zn(2+) ions in the dimer interface. Tandem G5 domains associate in a modular fashion, suggesting a "zinc zipper" mechanism for G5 domain-based intercellular adhesion in staphylococcal biofilms. We demonstrate, using a biofilm plate assay, that Zn(2+) chelation specifically prevents biofilm formation by S. epidermidis and methicillin-resistant S. aureus (MRSA). Furthermore, individual soluble G5 domains inhibit biofilm formation in a dose-dependent manner. Thus, the complex three-dimensional architecture of staphylococcal biofilms results from the self-association of a single type of protein domain. Surface proteins with tandem G5 domains are also found in other bacterial species, suggesting that this mechanism for intercellular adhesion in biofilms may be conserved among staphylococci and other Gram-positive bacteria. Zn(2+) chelation represents a potential therapeutic approach for combating biofilm growth in a wide range of bacterial biofilm-related infections.

The role of sigmaB in persistence of Staphylococcus epidermidis foreign body infection

Staphylococcal biofilm formation depends on the transcription factor sigma(B). We further investigated the role of sigma(B) in biofilm formation and persistence in vitro and in vivo in a subcutaneous rat model. As expected, expression of all sigma(B) operon genes was transiently higher in the first 6 h of biofilm formation compared to planktonic bacteria, concurrent with a temporary upregulation of icaA and aap expression. However, we also observed a second upregulation of sigB expression in biofilm more than 2 days old without upregulation of icaA or aap. Biofilm formation by Staphylococcus epidermidis strains 8400 and 1457 was compared to that of isogenic mutants with inactivation of rsbU, of rsbUVW and of the entire sigma(B) operon. Both wild-type strains and the constitutively sigB-expressing rsbUVW mutant showed a strong biofilm-positive phenotype. The rsbUVW mutant biofilm was, however, thinner and more evenly spread than the wild-type biofilm. Inactivation of SigB in the rsbUVWsigB mutant or mutation of the positive regulator RsbU reduced both the number of sessile bacteria and polysaccharide intercellular adhesin (PIA) synthesis. These differences between the wild-types and their respective mutants appeared after 6 h in in vitro biofilms but only after 4 days in in vivo biofilms. Our results provide additional evidence for a role for sigma(B) in biofilm formation. They also suggest a role for sigma(B) in biofilm maturation and stability that is independent of PIA or accumulation-associated protein (Aap) and point to significant differences in the temporal development between in vitro and in vivo biofilms.

Biofilm and the role of the ica operon and aap in Staphylococcus epidermidis isolates causing neurosurgical meningitis

Fifty-five Staphylococcus epidermidis isolates, classified as contaminants or causing device-related meningitis, from external ventricular drain (EVD) and non-EVD cerebrospinal fluid specimens were characterized. Thirty-three of 42 (78.6%) meningitis isolates were PCR-positive for ica and aap, known determinants of polysaccharide- and protein-mediated biofilm production, whereas five of 13 (38.5%) contaminants were ica- and aap-negative; 71.4% of meningitis isolates and 84.6% of contaminants produced biofilm. ica+aap+ meningitis isolates produced more biofilm than ica+aap- isolates (p 0.0020). ica+aap- isolates did not produce more biofilm than ica-aap+ isolates (p 0.4368). Apparently, ica and aap are associated with biofilm production in S. epidermidis device-related meningitis isolates.

SarZ is a key regulator of biofilm formation and virulence in Staphylococcus epidermidis

Biofilm-associated infection due to Staphylococcus epidermidis, the leading nosocomial pathogen, is a major problem for the public health system, but the regulation of this important phenotype is not completely understood. Using a highly discriminatory screening procedure for genes that influence biofilm formation, we identified the transcriptional regulator SarZ as a novel important determinant of biofilm formation and biofilm-associated infection, on the basis of the significant impact of sarZ on the transcription of the biosynthetic operon for biofilm exopolysaccharide. In addition, sarZ influenced the expression of a series of virulence genes, including genes that influence the expression of lipases and proteases, resistance to an important human antimicrobial peptide, and hemolysis. Our study indicates that the SarZ regulator has a key role in maintaining the typical S. epidermidis phenotype, which is characterized by pronounced biofilm formation and immune evasion, a likely reason for the success of S. epidermidis as a colonizing organism and pathogen in chronic, biofilm-associated infection.

A novel Staphylococcus aureus biofilm phenotype mediated by the fibronectin-binding proteins, FnBPA and FnBPB

Device-associated infections involving biofilm remain a persistent clinical problem. We recently reported that four methicillin-resistant Staphylococcus aureus (MRSA) strains formed biofilm independently of the icaADBC-encoded exopolysaccharide. Here, we report that MRSA biofilm development was promoted under mildly acidic growth conditions triggered by the addition of glucose to the growth medium. Loss of sortase, which anchors LPXTG-containing proteins to peptidoglycan, reduced the MRSA biofilm phenotype. Furthermore introduction of mutations in fnbA and fnbB, which encode the LPXTG-anchored multifunctional fibrinogen and fibronectin-binding proteins, FnBPA and FnBPB, reduced biofilm formation by several MRSA strains. However, these mutations had no effect on biofilm formation by methicillin-sensitive S. aureus strains. FnBP-promoted biofilm occurred at the level of intercellular accumulation and not primary attachment. Mutation of fnbA or fnbB alone did not substantially affect biofilm, and expression of either gene alone from a complementing plasmid in fnbA fnbB mutants restored biofilm formation. FnBP-promoted biofilm was dependent on the integrity of SarA but not through effects on fnbA or fnbB transcription. Using plasmid constructs lacking regions of FnBPA to complement an fnbAB mutant revealed that the A domain alone and not the domain required for fibronectin binding could promote biofilm. Additionally, an A-domain N304A substitution that abolished fibrinogen binding did not affect biofilm. These data identify a novel S. aureus biofilm phenotype promoted by FnBPA and FnBPB which is apparently independent of the known ligand-binding activities of these multifunctional surface proteins.

Skin microbiota: a source of disease or defence?

Microbes found on the skin are usually regarded as pathogens, potential pathogens or innocuous symbiotic organisms. Advances in microbiology and immunology are revising our understanding of the molecular mechanisms of microbial virulence and the specific events involved in the host-microbe interaction. Current data contradict some historical classifications of cutaneous microbiota and suggest that these organisms may protect the host, defining them not as simple symbiotic microbes but rather as mutualistic. This review will summarize current information on bacterial skin flora including Staphylococcus, Corynebacterium, Propionibacterium, Streptococcus and Pseudomonas. Specifically, the review will discuss our current understanding of the cutaneous microbiota as well as shifting paradigms in the interpretation of the roles microbes play in skin health and disease.

Staphylococcal biofilms

Staphylococcus epidermidis and Staphylococcus aureus are the most frequent causes of nosocomial infections and infections on indwelling medical devices, which characteristically involve biofilms. Recent advances in staphylococcal molecular biology have provided more detailed insight into the basis of biofilm formation in these opportunistic pathogens. A series of surface proteins mediate initial attachment to host matrix proteins, which is followed by the expression of a cationic glucosamine-based exopolysaccharide that aggregates the bacterial cells. In some cases, proteins may function as alternative aggregating substances. Furthermore, surfactant peptides have now been recognized as key factors involved in generating the three-dimensional structure of a staphylococcal biofilm by cell-cell disruptive forces, which eventually may lead to the detachment of entire cell clusters. Transcriptional profiling experiments have defined the specific physiology of staphylococcal biofilms and demonstrated that biofilm resistance to antimicrobials is due to gene-regulated processes. Finally, novel animal models of staphylococcal biofilm-associated infection have given us important information on which factors define biofilm formation in vivo. These recent advances constitute an important basis for the development of anti-staphylococcal drugs and vaccines.

Advancements in molecular epidemiology of implant infections and future perspectives

Implant infection remains the major and often irreducible complication in clinical use of biomaterials, demanding new therapeutic and preventive strategies. Etio-pathogenesis of biomaterials-related infections is being more and more studied, and various virulence bacterial factors have progressively been identified, but little is still known about the weight of the distinct molecules in the context of specific peri-implant infection sites. Molecular epidemiology has become recently integrated into the research on implant infections. What distinguishes molecular epidemiology from the simple molecular biology is that the use of molecular techniques is applied to the study of the distribution and prevalence of virulence and resistance genes in collections of bacterial clinical isolates from implant infections. Here, the authors comment on the range of molecular techniques available, reviewing the various applications of molecular epidemiology to the study of implant infections and providing some experimental examples related to the field of orthopaedic implant infections. They highlight the new opportunities arising from molecular epidemiology of designing measures useful to prevent and treat implant infections. The knowledge of the relative weight of virulence factors and of their regulatory mechanisms at molecular level can open the way to new strategies also including gene therapies aimed at silencing or knocking out crucial genes responsible for the aggressive tools (adhesins, biofilm production, antibiotic resistance) of the aetiological agents of implant-related infections.

Differential roles of poly-N-acetylglucosamine surface polysaccharide and extracellular DNA in Staphylococcus aureus and Staphylococcus epidermidis biofilms

Staphylococcus aureus and Staphylococcus epidermidis are major human pathogens of increasing importance due to the dissemination of antibiotic-resistant strains. Evidence suggests that the ability to form matrix-encased biofilms contributes to the pathogenesis of S. aureus and S. epidermidis. In this study, we investigated the functions of two staphylococcal biofilm matrix polymers: poly-N-acetylglucosamine surface polysaccharide (PNAG) and extracellular DNA (ecDNA). We measured the ability of a PNAG-degrading enzyme (dispersin B) and DNase I to inhibit biofilm formation, detach preformed biofilms, and sensitize biofilms to killing by the cationic detergent cetylpyridinium chloride (CPC) in a 96-well microtiter plate assay. When added to growth medium, both dispersin B and DNase I inhibited biofilm formation by both S. aureus and S. epidermidis. Dispersin B detached preformed S. epidermidis biofilms but not S. aureus biofilms, whereas DNase I detached S. aureus biofilms but not S. epidermidis biofilms. Similarly, dispersin B sensitized S. epidermidis biofilms to CPC killing, whereas DNase I sensitized S. aureus biofilms to CPC killing. We concluded that PNAG and ecDNA play fundamentally different structural roles in S. aureus and S. epidermidis biofilms.

Understanding the physiology and adaptation of staphylococci: A post-genomic approach

Staphylococcus aureus as well as coagulase-negative staphylococci are medically highly important pathogens characterized by an increasing resistance rate toward many antibiotics. Although normally being skin and mucosa commensals, some staphylococcal species and strains have the capacity to cause a wide range of infectious diseases. Many of these infections affect immunocompromised patients in hospitals. However, community-acquired staphylococcal infections due to resistant strains are also currently on the rise. In the light of this development, there is an urgent need for novel anti-staphylococcal therapeutic and prevention strategies for which a better understanding of the physiology of these bacteria is an essential prerequisite. Within the past years, staphylococci have been in the focus of genomic research, resulting in the determination and publication of a range of full-genome sequences of different staphylococcal species and strains which provided the basis for the design and application of DNA microarrays and other genomic tools. Here we summarize the results of the project group 'Staphylococci' within the research network 'Pathogenomics' giving new insights into the genome structure, molecular epidemiology, physiology, and genetic adaptation of both S. aureus and coagulase-negative staphylococci.

Persistent strains of coagulase-negative staphylococci in a neonatal intensive care unit: virulence factors and invasiveness

Coagulase-negative staphylococci (CoNS) are the major cause of nosocomial bacteraemia in neonates. The aim of this study was to investigate whether persistent strains of CoNS possess specific bacterial characteristics as compared with sporadic non-cluster isolates. In total, 180 blood culture isolates (95 contaminants and 85 invasive isolates) obtained from a single neonatal unit over a 12-year period were studied. Pulsed-field gel electrophoresis (PFGE) identified 87 persistent CoNS strains (endemic clones). The two largest PFGE clusters belonged to a single clonal complex according to multilocus sequence typing. Patients colonised or infected with endemic clones were of lower gestational age than those infected with non-cluster strains. One Staphylococcus haemolyticus cluster appeared to selectively colonise and infect the most extreme pre-term infants. Endemic clones were characterised by high levels of antibiotic resistance and biofilm formation. All 51 isolates belonging to the two largest PFGE clusters were ica operon-positive. Genes encoding Staphylococcus epidermidis surface protein B and the production of phenol-soluble modulins (PSMs) were also more prevalent among endemic clones than among non-cluster strains. However, endemic clones were not more prevalent among invasive isolates than among contaminants. These findings indicate that multiple selective factors, including antibiotic resistance, biofilm formation, surface proteins with adhesive properties, and PSMs regulated by agr, increase the ability of CoNS to persist in a hospital environment. It may be more prudent, when searching for new therapeutic targets, to focus on ubiquitous components of CoNS instead of putative virulence factors that do not clearly contribute to increased invasive capacity.

ica and beyond: biofilm mechanisms and regulation in Staphylococcus epidermidis and Staphylococcus aureus

Recent progress in elucidating the role of the icaADBC-encoded polysaccharide intercellular adhesin (PIA) or polymeric N-acetyl-glucosamine (PNAG) in staphylococcal biofilm development has in turn contributed significantly to our understanding of the pathogenesis of device-related infections. Nevertheless, our understanding of how the ica locus and PIA/PNAG biosynthesis are regulated is far from complete and many questions remain. Moreover, beyond ica, evidence is now emerging for the existence of ica-independent biofilm mechanisms in both Staphylococcus aureus and Staphylococcus epidermidis. Teichoic acids, which are a major carbohydrate component of the S. epidermidis biofilm matrix and the major cell wall autolysin, play an important role in the primary attachment phase of biofilm development, whereas the cell surface biofilm-associated protein and accumulation-associated protein are capable of mediating intercellular accumulation. These findings raise the exciting prospect that other surface proteins, which typically function as antigenic determinants or in binding to extracellular matrix proteins, may also act as biofilm adhesins. Given the impressive array of surface proteins expressed by S. aureus and S. epidermidis, future research into their potential role in biofilm development either independent of PIA/PNAG or in cooperation with PIA/PNAG will be of particular interest.

Spontaneous switch to PIA-independent biofilm formation in an ica-positive Staphylococcus epidermidis isolate

The ability to form biofilms on abiotic surfaces is considered a major step in Staphylococcus epidermidis pathogenesis. In the majority of isolates, biofilm formation is mediated by the production of the polysaccharide intercellular adhesin PIA which is synthesized by enzymes encoded by the ica operon. Here, we report on a spontaneous switch to proteinaceous biofilm formation in an S. epidermidis icaC::IS256 insertion mutant. Atomic force microscopy analysis of both PIA-dependent and proteinaceous biofilm revealed remarkable differences in biofilm substructures: the PIA-dependent biofilm was characterized by the presence of fibrous, net-like structures which were absent in proteinaceous biofilm. Transcription of aap, encoding the accumulation-associated protein Aap, was enhanced in a variant producing proteinaceous biofilm, while transcription of the Bap-homologous protein gene bhp was down-regulated. Regulation of PIA-independent biofilm differed from the wild type. Thus, ethanol induced proteinaceous biofilm formation, whereas NaCl abolished PIA-independent biofilm formation completely. The combined data indicate that biofilm formation in S. epidermidis is obviously ensured by more than one mechanism suggesting that this life style represents a crucial factor for this organism.

Formation and properties of in vitro biofilms of ica-negative Staphylococcus epidermidis clinical isolates

Coagulase-negative Staphylococcus epidermidis has become the leading cause of foreign-body infections due to its biofilm formation on all kinds of medical-device surfaces. The biofilm development of S. epidermidis includes two steps: the initial attachment phase and the accumulative phase. In the accumulative phase, the polysaccharide intercellular adhesin (PIA), encoded by the icaADBC locus, is the major component mediating intercellular adhesion. However, recent studies have revealed the emergence of biofilm-positive/ica-negative staphylococcal clinical isolates. In this report, two ica-negative S. epidermidis clinical strains, SE1 and SE4, exhibited their heterogeneity in biofilm architecture under static and flow conditions, compared with the biofilm-positive/ica-positive RP62A strain. Strains with this type of absence of PIA from biofilms also displayed intermediate resistance to vancomycin. More importantly, the cells of both SE1 and SE4 strains were more tolerant than those of RP62A to exposure to lysostaphin and vancomycin. Based on the results, it is suggested that the biofilm-positive/ica-negative strain represents a newly emergent subpopulation of S. epidermidis clinical strains, arising from selection by antibiotics in the nosocomial milieu, which displays a survival advantage in its host environment. Recent epidemiological data support this suggestion, by showing a tendency towards an increasing proportion of this subpopulation in staphylococci-associated infections.

Characterization of coagulase-negative staphylococci isolated from patients with infected hip prostheses: use of phenotypic and genotypic analyses, including tests for the presence of the ica operon

The aim of this study was to investigate phenotypic and/or genotypic heterogeneity in coagulase-negative staphylococci (CoNS) obtained from multiple tissue samples taken perioperatively during exchange surgery from each of 19 patients with clinically and/or microbiologically proven hip prosthesis infections. CoNS are important pathogens in prosthetic hip joint infections. Several virulence factors have been suggested for CoNS, such as phenotypic variation, yet the pathogenic processes that are involved remain unclear. The PhenePlate system (PhPlate AB, Stockholm Sweden) was used for phenotyping and pulsed-field gel electrophoresis for genotyping of polymorphisms in isolates of CoNS. Furthermore, polymerase chain reaction was used to determine the presence of the icaADB gene complex in the isolates. Some patients were infected with CoNS and other species, some were infected with multiple CoNS species, although infections with Staphylococcus epidermidis alone were most common, and some were infected with different S. epidermidis clones. Phenotypic variation was found among isolates both from the same tissue sample and from different samples from the same patient, and in some cases such variation represented the presence of different clones. One-third of the patients infected with S. epidermidis carried the icaADB genes. CoNS isolates showing phenotypic and/or genotypic heterogeneity were identified in tissue samples from half of the patients. The presence of the intercellular adhesion (ica) operon does not seem to be a prerequisite for establishing infection with CoNS.

Localized tufts of fibrils on Staphylococcus epidermidis NCTC 11047 are comprised of the accumulation-associated protein

Staphylococcus epidermidis is both a human skin commensal and an opportunistic pathogen, causing infections linked to implanted medical devices. This paper describes localized tufts of fibrillar appendages on a subpopulation (25%) of wild-type (WT) S. epidermidis NCTC 11047 cells. The fibrils (122.2 +/- 10.8 nm long) are usually in a lateral position on the cells. Fibrillar (Fib(+)) and nonfibrillar (Fib(-)) subpopulations were separated (enriched) by 34 sequential partitions of WT cells between a buffer phase and a hexadecane phase. Following enrichment, hydrophobic cells from the hexadecane phase comprised 70% Fib(+) cells and the less hydrophobic cells from the buffer phase entirely comprised Fib(-) cells. The Fib(+) and Fib(-) subpopulations did not revert on subculture (34 times) on solid medium. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of cell surface proteins from WT, Fib(+), and Fib(-) cells revealed two high-molecular-mass proteins (280 kDa and 230 kDa) on the WT and Fib(+) cells that were absent from the Fib(-) cells. Amino acid sequencing revealed that fragments of both the 280- and 230-kDa proteins had 100% identity to the accumulation-associated protein (Aap). Aap is known to cause biofilm formation if it is truncated by loss of the terminal A domain. Immunogold staining with anti-Aap antibodies labeled tuft fibrils of the WT and Fib(+) cells but not the cell surface of Fib(-) cells. The tufts were labeled with N-terminally directed antibodies (anti-A domain), showing that the fibrillar Aap was not truncated on the cell surface. Thus, the presence of full-length Aap correlated with the low biofilm-forming abilities of both WT and Fib(+) S. epidermidis NCTC 11047 populations. Reverse transcription-PCR showed that aap was transcribed in both Fib(+) and Fib(-) cells. We therefore propose that full-length Aap is expressed on cells of S. epidermidis NCTC 11047 as tufts of short fibrils and that fibril expression is regulated at a posttranscriptional level.

Peri-implant tissue is an important niche for Staphylococcus epidermidis in experimental biomaterial-associated infection in mice

Biomaterial-associated infections (BAI), which are predominantly caused by Staphylococcus epidermidis, are a significant problem in modern medicine. Biofilm formation is considered the pivotal element in the pathogenesis, but in previous mouse studies we retrieved S. epidermidis from peri-implant tissue. To assess the kinetics and generality of tissue colonization, we investigated BAI using two S. epidermidis strains, two biomaterials, and two mouse strains. With small inocula all implants were culture negative, whereas surrounding tissues were positive. When higher doses were used, tissues were culture positive more often than implants, with higher numbers of CFU. This was true for the different biomaterials tested, for both S. epidermidis strains, at different times, and for both mouse strains. S. epidermidis colocalized with host cells at a distance that was >10 cell layers from the biomaterial-tissue interface. We concluded that in mouse experimental BAI S. epidermidis peri-implant tissue colonization is more important than biofilm formation.

Biofilm formation in medical device-related infection

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.

Correlation between biofilm formation and production of polysaccharide intercellular adhesin in clinical isolates of coagulase-negative staphylococci

The ability to form a biofilm seems to play an essential role in the virulence of coagulase-negative staphylococci (CoNS) by permitting them to cause persistent prosthetic device-related infections. The most clearly characterized component of staphylococcal biofilms is the polysaccharide intercellular adhesin (PIA) encoded by the icaADBC operon. In the present paper, we assess the link between the ability to form a biofilm (Bf+/-), to synthesize PIA (PIA+/-) and the presence of the ica locus (ica+/-). For this purpose, 66 CoNS strains were tested in vitro. Seventy three percent of all strains revealed presence of the ica locus (ica+), and therefore were potentially able to produce PIA and to form a biofilm. However, the characteristics observed indicated that 15% of all strains were biofilm forming without PIA production (Bf+, PIA-, ica+/-) while 8% were PIA producers without biofilm formation (Bf-, PIA+, ica+). On the basis of the obtained data we conclude that (i) PIA synthesis alone is not sufficient to produce a biofilm and (ii) staphylococci can also form a biofilm without producing PIA.

Microbial interactions in Staphylococcus epidermidis biofilms

Medical device-associated infections, most frequently caused by coagulase-negative staphylococci, especially Staphylococcus epidermidis, are of increasing importance in modern medicine. The formation of adherent, multilayered bacterial biofilms is the most important factor in the pathogenesis of these infections, which regularly fail to respond to appropriate antimicrobial therapy. Progress in elucidating the factors functional in elaboration of S. epidermidis biofilms and the regulation of their expression with a special emphasis on the role of quorum sensing are reviewed. Significant progress has been made in recent years, which provides the rationale for developing better preventive, therapeutic and diagnostic measures.

Comparative proteomic analysis between the invasive and commensal strains ofStaphylococcus epidermidis

Staphylococcus epidermidis is one of the major causative agents for nosocomial infections. To reveal the pathogenesis factors, we performed the comparative proteomic analysis of invasive ATCC35984 and commensal ATCC12228 strains by two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry. The differentially expressed proteins were involved in carbohydrate metabolism, sugar binding, lipid degradation and amino acid binding. In addition, we demonstrated that the trap gene was transcribed by 3.657+/-0.156 (P<0.01) -fold higher in ATCC35984 than in ATCC12228. Levels of accumulation-associated protein (AAP) were found to be low by the immuno-dot blotting assay in ATCC12228, which is unable to form biofilm. Our results suggest that the target of RNAIII activating protein and AAP may contribute to S. epidermidis virulence and biofilm formation.

Biofilm matrix of Candida albicans and Candida tropicalis: chemical composition and role in drug resistance

Matrix material was extracted from biofilms of Candida albicans and Candida tropicalis and analysed chemically. Both preparations contained carbohydrate, protein, hexosamine, phosphorus and uronic acid. However, the major component in C. albicans matrix was glucose (32 %), whereas in C. tropicalis matrix it was hexosamine (27 %). Biofilms of C. albicans were more easily detached from plastic surfaces by treatment with the enzyme lyticase (β-1,3-glucanase) than were those of C. tropicalis. Biofilms of C. albicans were also partially detached by treatment with proteinase K, chitinase, DNase I, or β-N-acetylglucosaminidase, whereas C. tropicalis biofilms were only affected by lipase type VII or chitinase. To investigate a possible role for the matrix in biofilm resistance to antifungal agents, biofilms of C. albicans were grown under conditions of continuous flow in a modified Robbins device (MRD). These biofilms produced more matrix material than those grown statically, and were significantly more resistant to amphotericin B. Biofilms of C. tropicalis synthesized large amounts of matrix material even when grown statically, and such biofilms were completely resistant to both amphotericin B and fluconazole. Mixed-species biofilms of C. albicans and a slime-producing strain of Staphylococcus epidermidis (RP62A), when grown statically or in the MRD, were also completely resistant to amphotericin B and fluconazole. Mixed-species biofilms of C. albicans and a slime-negative mutant of S. epidermidis (M7), on the other hand, were completely drug resistant only when grown under flow conditions. These results demonstrate that the matrix can make a significant contribution to drug resistance in Candida biofilms, especially under conditions similar to those found in catheter infections in vivo, and that the composition of the matrix material is an important determinant in resistance.

An in vitro study of adherence of coagulase-negative staphylococci to bone chip columns

Coagulase-negative staphylococci (CNS) have become a dominant cause of bone infections and their adherence to the infected bones is a prerequisite for the initiation of these infections. In the present study we investigated and compared the adherence of CNS bacteria to human, chicken and rabbit bones. The study was performed using columns made of bone powder from the three different sources, and measurement of the extent of adhesion to bones of CNS bacteria as an in vitro model which is based on particles of matrix that are closely related to the natural matrix. The adhesion to rabbit bone was relatively high, while adhesion to both human and chicken bone columns was lower and almost identical. Pretreatment of the CNS bacteria with sodium periodate, beta-galactosidase or proteinase K significantly inhibited by 50-60% the adhesion to human bones. Pretreatment of CNS bacteria with subinhibitory concentrations of vancomycin or tunicamycin increased their adherence to human bones several-fold. When the bones were pretreated with vancomycin a considerable increase in the adhesion rate of the bacteria to human and chicken bones was seen. A smaller increase in adherence was observed after pretreatment of human bones with the antibiotic tunicamycin. Salicylic acid or benzalkonium chloride (BZC) also resulted in an increase in adhesion to these pretreated bones. From the results obtained it seems that pretreatment of the CNS bacteria with certain reagents exposes adhesins on the surface of the CNS bacteria. On the other hand, pretreatment of the bones with other reagents may enable a better exposure of receptors located on the bone cells and, as a consequence, may improve the adhesion of the CNS bacteria to the treated bones.

Proteomic profiling of cell envelope-associated proteins from Staphylococcus aureus

The emergence of highly virulent community acquired Staphylococcus aureus and continued progression of resistance to multiple antimicrobials, including methicillin and vancomycin, marks the reemergence of S. aureus as a serious health care threat. Investigation of proteins localized to the cell surface could help to elucidate mechanisms of virulence and antibiotic resistance in S. aureus. In this study, proteomic profiling methods were developed to solubilize, display, and evaluate abundance levels of proteins present in the supernatants of the lysostaphin-digested cell envelope from cultured vancomycin-intermediate S. aureus (VISA) cells. Combining approaches of 2-DE or chromatographic separation of proteins with MS analyses resulted in the identification of 144 proteins of particular interest. Of these proteins, 48 contained predicted cell wall localization or export signal motifs, including 14 with distinct covalent peptidoglycan-anchor sites, four of which are uncharacterized to date. One of the two most abundant cell envelope proteins, which showed remarkably high variations in MW and pI in the 2-DE gel display, was the S. aureus surface protein G. The display of numerous secreted proteins that are not covalently cell wall-anchored, suggests that, in the exponential growth phase, secreted proteins can be retained physiologically in the cell envelope and may interact with cell wall-anchored proteins and carbohydrate structures in a manner yet to be determined. The remaining 96 proteins, devoid of recognizable motifs, were repeatedly profiled in the VISA cell envelope fractions. We describe a novel semiquantitative method to determine abundance factors of such proteins in 2-DE gels of cell envelope fractions relative to whole cell lysates and discuss these data in the context of true cell envelope localization versus experimentally caused cell lysis.

Isolation of a strictly anaerobic strain of Staphylococcus epidermidis

Staphylococcus epidermidis is a well-characterized, nonfastidious, aerobic gram-positive coccus commonly isolated in the clinical microbiology laboratory. Although coagulase-negative staphylococci, including Staphylococcus epidermidis, are often considered a contaminant in the clinical laboratory, an increasing number of reports describe their pathogenesis, in particular in infections of prosthetic devices. This article describes the isolation of a strictly anaerobic strain of Staphylococcus epidermidis in pure culture from the site of an infected prosthetic hip. This isolate was unique in that it grew only under strictly anaerobic conditions. Initially, the isolate was thought to be a known anaerobic gram-positive coccus. However, certain key biochemical and antimicrobial tests performed as part of the standard laboratory identification procedure were not consistent with results expected for any known anaerobic gram-positive coccus; the isolate was catalase positive and metronidazole and penicillin resistant. This isolate was characterized by further biochemical analysis, antimicrobial testing, and nucleic acid sequencing. This paper presents the first documented isolation of a strictly anaerobic Staphylococcus epidermidis strain, confirmed by rpoB gene sequencing.

Comparative proteome analysis of Staphylococcus aureus biofilm and planktonic cells and correlation with transcriptome profiling

Pathogenic staphylococci can form biofilms in which they show a higher resistance to antibiotics and the immune defense system than their planktonic counterparts, which suggests that the cells in a biofilm have an altered metabolic activity. Here, 2-D PAGE was used to identify secreted, cell wall-associated and cytoplasmic proteins expressed in Staphylococcus aureus after 8 and 48 h of growth. The proteins were separated at pH ranges of 4-7 or 6-11. The protein patterns revealed significant differences in 427 protein spots; from these, 258 non-redundant proteins were identified using ESI-MS/MS. Biofilm cells expressed higher levels of proteins associated with cell attachment and peptidoglycan synthesis, and in particular fibrinogen-binding proteins. Enzymes involved in pyruvate and formate metabolism were upregulated. Furthermore, biofilm cells expressed more staphylococcal accessory regulator A protein (SarA), which corroborates the positive effect of SarA on the expression of the intercellular adhesion operon ica and biofilm growth. In contrast, proteins, such as proteases and particularly immunodominant antigen A (IsaA) and staphylococcal secretory antigen (SsaA), were found in lower amounts. The RNA expression profiling largely supports the proteomic data. The results were mapped onto KEGG pathways.

Commensal isolates of methicillin-resistant Staphylococcus epidermidis are also well equipped to produce biofilm on polystyrene surfaces

OBJECTIVES

To study biofilm production and to detect icaAD, atlE and aap genes in 137 isolates of methicillin-resistant Staphylococcus epidermidis (MRSE) obtained from healthy individuals from the community (35 isolates), from hospitalized patients at the Antônio Pedro University Hospital (25 isolates) and from individuals from a home-care system (HCS; 77 isolates).

METHODS

Biofilm production was determined in vitro using polystyrene inert surfaces. icaAD, atlE and aap genes were detected using PCR. Hybridization experiments were also carried out to confirm some PCR results. Antimicrobial susceptibility testing was carried out using the NCCLS methods.

RESULTS

Although many of the commensal MRSE isolates produced biofilms, the percentage of biofilm producers was significantly higher (P = 0.0107) among hospital isolates (76%) than among isolates from the community (60%) and from the HCS (57%). An association was observed between multiresistance and biofilm production for isolates obtained from healthy individuals from the community and from household contacts from the HCS (P < 0.0001). The concomitant presence of the ica operon and atlE and aap genes was associated with the strong biofilm-producer phenotype (P < 0.0001).

CONCLUSION

Because many of the commensal MRSE isolates obtained from nares produced biofilms and carried icaAD, aap and atlE genes, biofilms or such genetic elements should not be used as markers for clinical significance. The biofilm environment seems to increase genetic exchanges and hence may contribute to multiresistance phenotypes.

Role of silver ions in destabilization of intermolecular adhesion forces measured by atomic force microscopy in Staphylococcus epidermidis biofilms

In this paper, we report on the potential use of atomic force microscopy (AFM) as a tool to measure the intermolecular forces in biofilm structures and to study the effect of silver ions on sessile Staphylococcus epidermidis cell viability and stability. We propose a strategy of destabilizing the biofilm matrix by reducing the intermolecular forces within the extracellular polymeric substances (EPSs) using a low concentration (50 ppb) of silver ions. Our AFM studies on the intermolecular forces within the EPSs of S. epidermidis RP62A and S.epidermidis 1457 biofilms suggest that the silver ions can destabilize the biofilm matrix by binding to electron donor groups of the biological molecules. This leads to reductions in the number of binding sites for hydrogen bonds and electrostatic and hydrophobic interactions and, hence, the destabilization of the biofilm structure.

Sortases and the art of anchoring proteins to the envelopes of gram-positive bacteria

The cell wall envelopes of gram-positive bacteria represent a surface organelle that not only functions as a cytoskeletal element but also promotes interactions between bacteria and their environment. Cell wall peptidoglycan is covalently and noncovalently decorated with teichoic acids, polysaccharides, and proteins. The sum of these molecular decorations provides bacterial envelopes with species- and strain-specific properties that are ultimately responsible for bacterial virulence, interactions with host immune systems, and the development of disease symptoms or successful outcomes of infections. Surface proteins typically carry two topogenic sequences, i.e., N-terminal signal peptides and C-terminal sorting signals. Sortases catalyze a transpeptidation reaction by first cleaving a surface protein substrate at the cell wall sorting signal. The resulting acyl enzyme intermediates between sortases and their substrates are then resolved by the nucleophilic attack of amino groups, typically provided by the cell wall cross bridges of peptidoglycan precursors. The surface protein linked to peptidoglycan is then incorporated into the envelope and displayed on the microbial surface. This review focuses on the mechanisms of surface protein anchoring to the cell wall envelope by sortases and the role that these enzymes play in bacterial physiology and pathogenesis.