Characterization of a sar homolog of Staphylococcus epidermidis

Modified oxylipins as inhibitors of biofilm formation in Staphylococcus epidermidis

New approaches to combating microbial drug resistance are being sought, with the discovery of biofilm inhibitors considered as alternative arsenal for treating infections. Natural products have been at the forefront of antimicrobial discovery and serve as inspiration for the design of new antibiotics. We probed the potency, selectivity, and mechanism of anti-biofilm activity of modified oxylipins inspired by the marine natural product turneroic acid. Structure-activity relationship (SAR) evaluation revealed the importance of the trans-epoxide moiety, regardless of the position, for inhibiting biofilm formation. trans-12,13-epoxyoctadecanoic acid (1) and trans-9,10 epoxyoctadecanoic acid (4) selectively target the early stage of biofilm formation, with no effect on planktonic cells. These compounds interrupt the formation of a protective polysaccharide barrier by significantly upregulating the ica operon's transcriptional repressor. This was corroborated by docking experiment with SarA and scanning electron micrographs showing reduced biofilm aggregates and the absence of thread-like structures of extrapolymeric substances. In silico evaluation revealed that 1 and 4 can interfere with the AgrA-mediated communication language in Staphylococci, typical to the diffusible signal factor (DSF) capacity of lipophilic chains.

Molecular Genetics of Staphylococcus Epidermidis Biofilms on Indwelling Medical Devices

Staphylococcus epidermidis is an opportunistic pathogen associated with foreign body infections and nosocomial sepsis. The pathogenicity of S. epidermidis is mostly due to its ability to colonize indwelling polymeric devices and form a thick, multilayered biofilm. Biofilm formation is a major problem in treating S. epidermidis infection as biofilms provide significant resistance to antibiotics and to components of the innate host defenses. Various cell surface associated bacterial factors play a role in adherence and accumulation of the biofilm such as the polysaccharide intercellular adhesin and the autolysin AtlE. Furthermore, recent studies have shown that global regulators such as the agr quorum sensing system, the transcriptional regulator sarA and the alternative sigma factor sigB have an important function in the regulation of biofilm formation. Understanding the many complex mechanisms involved in biofilm formation is a key factor in the search for new anti-staphylococcal therapeutics.

Regulation of Biofilm Formation by σB is a Common Mechanism in Staphylococcus Epidermidis and is not Mediated by Transcriptional Regulation of sarA

Biofilm formation is a major pathogenetic factor of Staphylococcus epidermidis. In S. epidermidis the alternative sigma factor σB was identified to regulate biofilm formation in S. epidermidis 1457. In S. aureus σB dependent regulation plays a minor role, whereas sarA (Staphylococcus accessory regulator) is an essential regulator. Therefore, we investigated the impact of σB on sarA transcription and biofilm formation in three independent S. epidermidis isolates. Mutants with dysfunctional σB displayed a strongly reduced biofilm formation, whereas in mutants with constitutive σB activity bio film formation was increased. Transcriptional analysis revealed that IcaA transcription was down-regulated in all σB negative mutants while icaR transcription was up-regulated. However, transcriptional differences varied between individual strains, indicating that additional σB-dependent regulators are involved in biofilm expression. Interestingly, despite the presence of a σB promoter beside two σA promoters no differences, or only minor ones, were observed in sarA transcription, indicating that σB-dependent sarA transcript has no influence on the phenotypic changes. The data observed in independent clinical S. epidermidis isolates suggests that, in contrast to S. aureus, regulation of biofilm formation by σB is a general feature in S. epidermidis. Additionally, we were able to demonstrate that the sarA- dependent regulation is not involved in this regulatory pathway.

Structural basis of Staphylococcus epidermidis biofilm formation: mechanisms and molecular interactions

Staphylococcus epidermidis is a usually harmless commensal bacterium highly abundant on the human skin. Under defined predisposing conditions, most importantly implantation of a medical device, S. epidermidis, however, can switch from a colonizing to an invasive life style. The emergence of S. epidermidis as an opportunistic pathogen is closely linked to the biofilm forming capability of the species. During the past decades, tremendous advance regarding our understanding of molecular mechanisms contributing to surface colonization has been made, and detailed information is available for several factors active during the primary attachment, accumulative or dispersal phase of biofilm formation. A picture evolved in which distinct factors, though appearing to be redundantly organized, take over specific and exclusive functions during biofilm development. In this review, these mechanisms are described in molecular detail, with a highlight on recent insights into multi-functional S. epidermidis cell surface proteins contributing to surface adherence and intercellular adhesion. The integration of distinct biofilm-promoting factors into regulatory networks is summarized, with an emphasis on mechanism that could allow S. epidermidis to flexibly adapt to changing environmental conditions present during colonizing or invasive life-styles.

Coagulase-negative staphylococci

The definition of the heterogeneous group of coagulase-negative staphylococci (CoNS) is still based on diagnostic procedures that fulfill the clinical need to differentiate between Staphylococcus aureus and those staphylococci classified historically as being less or nonpathogenic. Due to patient- and procedure-related changes, CoNS now represent one of the major nosocomial pathogens, with S. epidermidis and S. haemolyticus being the most significant species. They account substantially for foreign body-related infections and infections in preterm newborns. While S. saprophyticus has been associated with acute urethritis, S. lugdunensis has a unique status, in some aspects resembling S. aureus in causing infectious endocarditis. In addition to CoNS found as food-associated saprophytes, many other CoNS species colonize the skin and mucous membranes of humans and animals and are less frequently involved in clinically manifested infections. This blurred gradation in terms of pathogenicity is reflected by species- and strain-specific virulence factors and the development of different host-defending strategies. Clearly, CoNS possess fewer virulence properties than S. aureus, with a respectively different disease spectrum. In this regard, host susceptibility is much more important. Therapeutically, CoNS are challenging due to the large proportion of methicillin-resistant strains and increasing numbers of isolates with less susceptibility to glycopeptides.

Biomolecular mechanisms of staphylococcal biofilm formation

The multitude of biomolecular and regulatory factors involved in staphylococcal adhesion and biofilm formation owe much to their ability to colonize surfaces, allowing the biofilm form to become the preferential bacterial phenotype. Judging by total number, biomass and variety of environments colonized, bacteria can be categorized as the most successful lifeform on earth. This is due to the ability of bacteria and other microorganisms to respond phenotypically via biomolecular processes to the stresses of their surrounding environment. This review focuses on the specific pathways involved in the adhesion of the Gram-positive bacteria Staphylococcus epidermidis and Staphylococcus aureus with reference to the role of specific cell surface adhesins, the ica operon, accumulation-associated proteins and quorum-sensing systems and their significance in medical device-related infection.

Biofilm formation in Staphylococcus implant infections. A review of molecular mechanisms and implications for biofilm-resistant materials

Implant infections in orthopaedics, as well as in many other medical fields, are chiefly caused by staphylococci. The ability of growing within a biofilm enhances the chances of staphylococci to protect themselves from host defences, antibiotic therapies, and biocides. Advances in scientific knowledge on structural molecules (exopolysaccharide, proteins, teichoic acids, and the most recently described extracellular DNA), on the synthesis and genetics of staphylococcal biofilms, and on the complex network of signal factors that intervene in their control are here presented, also reporting on the emerging strategies to disrupt or inhibit them. The attitude of polymorphonuclear neutrophils and macrophages to infiltrate and phagocytise biofilms, as well as the ambiguous behaviour exhibited by these innate immune cells in biofilm-related implant infections, are here discussed. Research on anti-biofilm biomaterials is focused, reviewing materials loaded with antibacterial substances, or coated with anti-adhesive/anti-bacterial immobilized agents, or surfaced with nanostructures. Latter approaches appear promising, since they avoid the spread of antibacterial substances in the neighbouring tissues with the consequent risk of inducing bacterial resistance.

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.

σBand SarA independently regulate polysaccharide intercellular adhesin production inStaphylococcus epidermidis

The production of polysaccharide intercellular adhesin (PIA) is an essential process in foreign body infections mediated by Staphylococcus epidermidis. Transcriptional regulation of the icaADBC operon, the genes responsible for production of enzymes that synthesize PIA, is multi-factorial and involves at least SarA and σB. Transcriptional and promoter fusion studies revealed that the decreased transcription of the icaADBC operon observed in a S. epidermidis 1457 sigB mutant is not mediated through a direct interaction of σB–RNA polymerase at the icaADBC promoter region but instead through the upregulation of IcaR, a known repressor of icaADBC transcription. Transcriptional analysis of a 1457 sigB–icaR double mutant confirmed that the decreased icaADBC transcript in 1457 sigB is IcaR dependent. Furthermore, primer extension studies suggest that the icaR promoter appears to be σAdependent, suggesting that σBindirectly controls icaR transcription through an unknown pathway. In addition, it was confirmed that the loss of SarA results in the loss of icaADBC transcription and PIA production in S. epidermidis. It was further demonstrated, through the over-production of SarA in 1457 sigB, that the loss of sarP1 promoter activity in 1457 sigB has little or no effect on the loss of PIA production in this mutant. Finally, it was demonstrated that PIA production could be restored in both 1457 sigB and 1457 sarA by complementing these mutants with a full-length icaADBC operon controlled by a cadmium-inducible noncognate promoter. It is concluded that σBand SarA operate independently of each other to regulate PIA production and biofilm development in S. epidermidis.Key words: Staphylococcus epidermidis, biofilm, σB, SarA, icaADBC.

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.

SarA is an essential positive regulator of Staphylococcus epidermidis biofilm development

Staphylococcus epidermidis biofilm formation is associated with the production of the polysaccharide intercellular adhesin (PIA)--poly-N-acetylglucosamine polysaccharide (PNAG) by the products of the icaADBC operon. Recent evidence indicates that SarA, a central regulatory element that controls the production of Staphylococcus aureus virulence factors, is essential for the synthesis of PIA/PNAG and the ensuing biofilm development in this species. Based on the presence of a sarA homolog, we hypothesized that SarA could also be involved in the regulation of the biofilm formation process in S. epidermidis. To investigate this, we constructed nonpolar sarA deletions in two genetically unrelated S. epidermidis clinical strains, O-47 and CH845. The SarA mutants were completely defective in biofilm formation, both in the steady-state conditions of a microtiter dish assay and in the flow conditions of microfermentors. Reverse transcription-PCR experiments showed that the mutation in the sarA gene resulted in downregulation of the icaADBC operon transcription in an IcaR-independent manner. Purified SarA protein showed high-affinity binding to the icaA promoter region by electrophoretic mobility shift assays. Consequently, mutation in sarA provoked a significant decrease in the amount of PIA/PNAG on the cell surface. Furthermore, heterologous complementation of S. aureus sarA mutants with the sarA gene of S. epidermidis completely restored biofilm formation. In summary, SarA appeared to be a positive regulator of transcription of the ica locus, and in its absence, PIA/PNAG production and biofilm formation were diminished. Additionally, we present experimental evidence showing that SarA may be an important regulatory element that controls S. epidermidis virulence factors other than biofilm formation.

Biofilm formation, icaADBC transcription, and polysaccharide intercellular adhesin synthesis by staphylococci in a device-related infection model

Biofilm formation of Staphylococcus epidermidis and S. aureus is mediated by the polysaccharide intercellular adhesin (PIA) encoded by the ica operon. We used a device-related animal model to investigate biofilm formation, PIA expression (immunofluorescence), and ica transcription (quantitative transcript analysis) throughout the course of infection by using two prototypic S. aureus strains and one S. epidermidis strain as well as corresponding ica mutants. During infection, the ica mutants were growth attenuated when inoculated in competition with the corresponding wild-type strains but not when grown singly. A typical biofilm was observed at the late course of infection. Only in S. aureus RN6390, not in S. aureus Newman, were PIA and ica-specific transcripts detectable after anaerobic growth in vitro. However, both S. aureus strains were PIA positive in vivo by day 8 of infection. ica transcription preceded PIA expression and biofilm formation in vivo. In S. epidermidis, both PIA and ica expression levels were elevated compared to those in the S. aureus strains in vitro as well as in vivo and were detectable throughout the course of infection. In conclusion, in S. aureus, PIA expression is dependent on the genetic background of the strain as well as on strong inducing conditions, such as those dominating in vivo. In S. epidermidis, PIA expression is elevated and less vulnerable to environmental conditions.

Inactivations of rsbU and sarA by IS256 represent novel mechanisms of biofilm phenotypic variation in Staphylococcus epidermidis

Expression of ica operon-mediated biofilm formation in Staphylococcus epidermidis RP62A is subject to phase variable regulation. Reversible transposition of IS256 into icaADBC or downregulation of icaADBC expression are two important mechanisms of biofilm phenotypic variation. Interestingly, the presence of IS256 was generally associated with a more rapid rate of phenotypic variation, suggesting that IS256 insertions outside the ica locus may affect ica transcription. Consistent with this, we identified variants with diminished ica expression, which were associated with IS256 insertions in the sigmaB activator rsbU or sarA. Biofilm development and ica expression were activated only by ethanol and not NaCl in rsbU::IS256 insertion variants, which were present in approximately 11% of all variants. sigmaB activity was impaired in rsbU::IS256 variants, as evidenced by reduced expression of the sigmaB-regulated genes asp23, csb9, and rsbV. Moreover, expression of sarA, which is sigmaB regulated, and SarA-regulated RNAIII were also suppressed. A biofilm-forming phenotype was restored to rsbU::IS256 variants only after repeated passage and was not associated with IS256 excision from rsbU. Only one sarA::IS256 insertion mutant was identified among 43 biofilm-negative variants. Both NaCl and ethanol-activated ica expression in this sarA::IS256 variant, but only ethanol increased biofilm development. Unlike rsbU::IS256 variants, reversion of the sarA::IS256 variant to a biofilm-positive phenotype was accompanied by precise excision of IS256 from sarA and restoration of normal ica expression. These data identify new roles for IS256 in ica and biofilm phenotypic variation and demonstrate the capacity of this element to influence the global regulation of transcription in S. epidermidis.

RsbU-dependent regulation of Staphylococcus epidermidis biofilm formation is mediated via the alternative sigma factor sigmaB by repression of the negative regulator gene icaR

Transposon mutagenesis of rsbU leads to a biofilm-negative phenotype in Staphylococcus epidermidis. However, the pathway of this regulatory mechanism was unknown. To investigate the role of RsbU in the regulation of the alternative sigma factor sigma(B) and biofilm formation, we generated different mutants of the sigma(B) operon in S. epidermidis strains 1457 and 8400. The genes rsbU, rsbV, rsbW, and sigB, as well as the regulatory cascade rsbUVW and the entire sigma(B) operon, were deleted. Transcriptional analysis of sarA and the sigma(B)-dependent gene asp23 revealed the functions of RsbU and RsbV as positive regulators and of RsbW as a negative regulator of sigma(B) activity, indicating regulation of sigma(B) activity similar to that characterized for Bacillus subtilis and Staphylococcus aureus. Phenotypic characterization of the mutants revealed that the dramatic decrease of biofilm formation in rsbU mutants is mediated via sigma(B), indicating a crucial role for sigma(B) in S. epidermidis pathogenesis. However, biofilm formation in mutants defective in sigma(B) or its function could be restored in the presence of subinhibitory ethanol concentrations. Transcriptional analysis revealed that icaR is up-regulated in mutants lacking sigma(B) function but that icaA transcription is down-regulated in these mutants, indicating a sigma(B)-dependent regulatory intermediate negatively regulating IcaR. Supplementation of growth media with ethanol decreased icaR transcription, leading to increased icaA transcription and a biofilm-positive phenotype, indicating that the ethanol-dependent induction of biofilm formation is mediated by IcaR. This icaR-dependent regulation under ethanol induction is mediated in a sigma(B)-independent manner, suggesting at least one additional regulatory intermediate in the biofilm formation of S. epidermidis.

Growth phase-dependent production of a cell wall-associated elastinolytic cysteine proteinase by Staphylococcus epidermidis

Staphylococcus epidermidis, a Gram-positive, coagulase-negative bacterium is a predominant inhabitant of human skin and mucous membranes. Recently, however, it has become one of the most important agents of hospital-acquired bacteriemia, as it has been found to be responsible for surgical wound infections developed in individuals with indwelling catheters or prosthetic devices, as well as in immunosupressed or neutropenic patients. Despite their medical significance, little is known about proteolytic enzymes of S. epidermidis and their possible contribution to the bacterium's pathogenicity; however, it is likely that they function as virulence factors in a manner similar to that proposed for the proteases of Staphylococcus aureus. Here we describe the purification of a cell wall-associated cysteine protease from S. epidermidis, its biochemical properties and specificity. A homology search using N-terminal sequence data revealed similarity to staphopain A (ScpA) and staphopain B (SspB), cysteine proteases from S. aureus. Moreover, the gene encoding S. epidermidis cysteine protease (Ecp) and a downstream gene coding for a putative inhibitor of the protease form an operon structure which resembles that of staphopain A in S. aureus. The active cysteine protease was detected on the bacterial cell surface as well as in the culture media and is apparently produced in a growth phase-dependent manner, with initial expression occurring in the mid-logarithmic phase. This enzyme, with elastinolytic properties, as well as the ability to cleave alpha1PI, fibrinogen and fibronectin, may possibly contribute to the invasiveness and pathogenic potential of S. epidermidis.

Staphylococcal accessory gene regulator (sar) as a signature gene to detect enterotoxigenic staphylococci

AIMS

To evaluate the use of a staphylococcal accessory gene regulator (sar) as a means of detecting enterotoxigenic staphylococci.

METHODS AND RESULTS

SarA gene-specific primers were designed and applied in PCR, which resulted in the detection of 49 sar-positive isolates from a total of 67 natural food isolates of staphylococci. Colony hybridization using PCR-generated Digoxigenin (DIG)-labelled sarA probe tested in spiked samples of khoa (a traditional heat-concentrated milk product) comprising a mixed microflora ensured the specificity of the probe. Validation experiments with the commercial samples of khoa also demonstrated the specificity of the probe. PCR characterization for enterotoxins A-D revealed the presence of at least one of the toxin-encoding genes in all the sarA-positive isolates tested.

CONCLUSION

The study indicated that sarA gene could be an ideal marker gene either in colony hybridization or in PCR, for an effective detection of potentially enterotoxigenic strains of staphylococci in a food system.

SIGNIFICANCE AND IMPACT OF THE STUDY

As an alternative to targeting the individual toxin genes, a regulatory gene responsible for controlling the synthesis of various virulence factors may be a suitable target gene for screening potentially toxigenic staphylococci in food system using nucleic acid-based methods.

Immunology of Staphylococcal biofilm infections in the eye: new tools to study biofilm endophthalmitis

Endophthalmitis is an important disease of the eye that is most frequently caused by postoperative and post-traumatic introduction of bacteria into the posterior segment of the eye. In the case of severe infections, visual acuity is greatly damaged or completely lost. Much work has focused on the ability of planktonic bacteria to cause infection and ocular damage while little work has focused on chronic infections in endophthalmitis mediated by the formation of bacterial biofilms on the surface of the lens. This review focuses on the interaction of Staphylococcus aureus and Staphylococcus epidermidis lens-associated biofilms in endophthalmitis. Additionally, this review highlights some relevant biofilm-immune system interactions and outlines a new in vivo mouse model to explore biofilm-related infections in endophthalmitis.

Staphylococcus epidermidis infections

The opportunistic human pathogen Staphylococcus epidermidis has become the most important cause of nosocomial infections in recent years. Its pathogenicity is mainly due to the ability to form biofilms on indwelling medical devices. In a biofilm, S. epidermidis is protected against attacks from the immune system and against antibiotic treatment, making S. epidermidis infections difficult to eradicate.

Molecular cloning and biochemical characterisation of proteases from Staphylococcus epidermidis

We report the complete coding sequence and the partial amino acid sequence (determined by chemical sequencing) of Staphylococcus epidermidis extracellular cysteine (Ecp) and serine (Esp) proteases. The first enzyme shows an extended sequence similarity to Staphylococcus aureus cysteine protease (staphopain) and the second one resembles the serine protease produced by that species. The region directly upstream of the sequence coding for the mature protein in both enzymes displays significant homology to the profragments encoded by sspB and sspA, respectively, thus suggesting that the characterised enzymes may also be produced as proproteins. Furthermore, we report some biological properties of the cysteine protease, contributing to a better understanding of its role as a possible virulence factor. The proteolytic activity of this enzyme was rapidly and efficiently inhibited by human alpha-2-macroglobulin; however, human kininogen as well as cystatins (A, C and D) were not inhibitory. Moreover, the protease was capable of inactivating, by limited proteolysis, both alpha-1-antitrypsin and HMW-kininogen, but neither alpha-1-antichymotrypsin nor antithrombin III.

SarT, a repressor of alpha-hemolysin in Staphylococcus aureus

In searching the Staphylococcus aureus genome, we found several homologs to SarA. One of these genes, sarT, codes for a basic protein with 118 residues and a predicted molecular size of 16,096 Da. Northern blot analysis revealed that the expression of sarT was repressed by sarA and agr. An insertion sarT mutant generated in S. aureus RN6390 and 8325-4 backgrounds revealed minimal effect on the expression of sarR and sarA. The RNAIII level was notably increased in the sarT mutant, particularly in postexponential-phase cells, while the augmentative effect on RNAII was less. SarT repressed the expression of alpha-hemolysin, as determined by Northern blotting, Western blotting, and a rabbit erythrocyte hemolytic assay. This repression was relieved upon complementation. Similar to agr and sarA mutants, which predictably displayed a reduction in hla expression, the agr sarT mutant exhibited a lower level of hla transcription than the sarT mutant. In contrast, hla transcription was enhanced in the sarA sarT mutant compared with the single sarA mutant. Collectively, these results indicated that the sarA locus, contrary to the regulatory action of agr, induced alpha-hemolysin production by repressing sarT, a repressor of hla transcription.

PCR-Based assay for discrimination between invasive and contaminating Staphylococcus epidermidis strains

The discrimination between Staphylococcus epidermidis strains that contaminate and infect blood cultures is a daily challenge for clinical laboratories. The results of PCR detection of putative virulence genes were compared for contaminating strains, sepsis-related strains, catheter strains, and saprophytic strains. Multiplex PCR was used to explore the atlE gene, which is involved in initial adherence, the intercellular adhesion gene cluster (ica), which mediates the formation of the biofilm, and the agrA, sarA, and mecA genes, which might contribute to the pathogenicity of S. epidermidis. Whereas the atlE, agrA, and sarA genes were almost ubiquitously amplified, the ica and mecA genes were detected significantly more in infecting strains than in contaminating strains (P </= 0.02) and thus appeared to be related to the potential virulence of S. epidermidis.