Staphylococcus aureus biofilms: properties, regulation, and roles in human disease

Propionibacterium acnes: from commensal to opportunistic biofilm-associated implant pathogen

Propionibacterium acnes is known primarily as a skin commensal. However, it can present as an opportunistic pathogen via bacterial seeding to cause invasive infections such as implant-associated infections. These infections have gained more attention due to improved diagnostic procedures, such as sonication of explanted foreign materials and prolonged cultivation time of up to 14 days for periprosthetic biopsy specimens, and improved molecular methods, such as broad-range 16S rRNA gene PCR. Implant-associated infections caused by P. acnes are most often described for shoulder prosthetic joint infections as well as cerebrovascular shunt infections, fibrosis of breast implants, and infections of cardiovascular devices. P. acnes causes disease through a number of virulence factors, such as biofilm formation. P. acnes is highly susceptible to a wide range of antibiotics, including beta-lactams, quinolones, clindamycin, and rifampin, although resistance to clindamycin is increasing. Treatment requires a combination of surgery and a prolonged antibiotic treatment regimen to successfully eliminate the remaining bacteria. Most authors suggest a course of 3 to 6 months of antibiotic treatment, including 2 to 6 weeks of intravenous treatment with a beta-lactam. While recently reported data showed a good efficacy of rifampin against P. acnes biofilms, prospective, randomized, controlled studies are needed to confirm evidence for combination treatment with rifampin, as has been performed for staphylococcal implant-associated infections.

Immunoproteomic Identification of In Vivo-Produced Propionibacterium acnes Proteins in a Rabbit Biofilm Infection Model

Propionibacterium acnes is well-known as a human skin commensal but can also act as an invasive pathogen causing implant-associated infections. In order to resolve these types of P. acnes infections, the implants must be removed, due to the presence of an established biofilm that is recalcitrant to antibiotic therapy. In order to identify those P. acnes proteins produced in vivo during a biofilm infection, we established a rabbit model of implant-associated infection with this pathogen. P. acnes biofilms were anaerobically grown on dextran beads that were then inoculated into the left tibias of rabbits. At 4 weeks postinoculation, P. acnes infection was confirmed by radiograph, histology, culture, and PCR. In vivo-produced and immunogenic P. acnes proteins were detected on Western blot using serum samples from rabbits infected with P. acnes after these bacterial proteins were separated by two-dimensional gel electrophoresis. Those proteins that bound host antibodies were then isolated and identified by tandem mass spectrometry. Radiographs and histology demonstrated a disruption in the normal bone architecture and adherent biofilm communities in those animals with confirmed infections. A total of 24 immunogenic proteins were identified; 13 of these proteins were upregulated in both planktonic and biofilm modes, including an ABC transporter protein. We successfully adapted a rabbit model of implant-associated infection for P. acnes to identify P. acnes proteins produced during a chronic biofilm-mediated infection. Further studies are needed to evaluate the potential of these proteins for either a diagnostic test or a vaccine to prevent biofilm infections caused by P. acnes.

Antibiosis interaction of Staphylococccus aureus on Aspergillus fumigatus assessed in vitro by mixed biofilm formation

Background

Microorganisms of different species interact in several ecological niches, even causing infection. During the infectious process, a biofilm of single or multispecies can develop. Aspergillus fumigatus and Staphyloccocus aureus are etiologic agents that can cause infectious keratitis. We analyzed in vitro single A. fumigatus and S. aureus, and mixed A. fumigatus-S. aureus biofilms. Both isolates were from patients with infectious keratitis. Structure of the biofilms was analyzed through microscopic techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), confocal, and fluorescence microscopy (CLSM) in mixed biofilm as compared with the single A. fumigatus biofilm.

Results

To our knowledge, this is the first time that the structural characteristics of the mixed biofilm A. fumigatus-A. fumigatus were described and shown. S. aureus sharply inhibited the development of biofilm formed by A. fumigatus, regardless of the stage of biofilm formation and bacterial inoculum. Antibiosis effect of bacterium on fungus was as follows: scarce production of A. fumigatus biofilm; disorganized fungal structures; abortive hyphae; and limited hyphal growth; while conidia also were scarce, have modifications in their surface and presented lyses. Antagonist effect did not depend on bacterial concentration, which could probably be due to cell-cell contact interactions and release of bacterial products. In addition, we present images about the co-localization of polysaccharides (glucans, mannans, and chitin), and DNA that form the extracellular matrix (ECM). In contrast, single biofilms showed extremely organized structures: A. fumigatus showed abundant hyphal growth, hyphal anastomosis, and channels, as well as some conidia, and ECM. S. aureus showed microcolonies and cell-to-cell bridges and ECM.

Conclusions

Herein we described the antibiosis relationship of S. aureus against A. fumigatus during in vitro biofilm formation, and report the composition of the ECM formed.

Biofilm formation by Staphylococcus aureus isolates from skin and soft tissue infections

Many diseases caused by Staphylococcus aureus are associated with biofilm formation. However, the ability of S. aureus isolates from skin and soft tissue infections to form biofilms has not yet been investigated. We tested 160 isolates from patients with various skin infections for biofilm-forming capacity in different growth media. All the isolates formed biofilms, the extent of which depended on the type of growth medium. The thickest biofilms were formed when both plasma and glucose were present in the broth; in this case, S. aureus incorporated host fibrin into the biofilm's matrix. There were no differences in the biofilm formation between isolates from different types of skin infections, except for a particularly good biofilm formation by isolates from diabetic wounds and a weaker biofilm formation by isolates from impetigo. In conclusion, biofilm formation is a universal behavior of S. aureus isolates from skin infections. In some cases, such as in diabetic wounds, a particularly strong biofilm formation most likely contributes to the chronic and recurrent character of the infection. Additionally, as S. aureus apparently uses host fibrin as part of the biofilm structure, we suggest that plasma should be included more frequently in in vitro biofilm studies.

The Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs) Genes among Clinical Isolates of Staphylococcus aureus from Hospitalized Children

BACKGROUND

Isolates of Staphylococcus aureus express a myriad of adhesive surface proteins that play important role in colonization of the bacteria on nasal and skin surfaces, beginning the process of pathogenesis. The aim of this study was to screen several of the Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs) genes among the isolate of S. aureus from hospitalized children.

METHODS

A total of 22 S. aureus isolates were collected from hospitalized children in Tehran from 2012 to 2013. Detection of the mecA and several adhesive surface proteins genes including clfA, B (encoding clumping factors A, B); fnbA, B (encoding finronectin binding proteins A, B); fib (encoding fibrinogen binding protein); eno (encoding laminin binding protein); cna (encoding collagen binding protein); ebps (encoding elastin binding protein) and bbp (encoding bone sialo-protein binding protein), was performed by PCR.

RESULTS

The clfAB genes were detected among all the isolates. The prevalence of fnbA, fnbB, fib, eno, cna, ebps and bbp was 63%, 6%, 50%, 59%, 82%, 63%, 9% and 0%, respectively.

CONCLUSION

The high prevalence of these genes is important for future plans in vaccine designation. MRSA and MSSA isolates similarly can produce adhesive surface proteins for colonization.

Bromophenazine derivatives with potent inhibition, dispersion and eradication activities against Staphylococcus aureus biofilms

Bacterial biofilms are surface-attached communities of bacteria that are: (1) highly prevalent in human infections, and (2) resistant to conventional antibiotic treatments and host immune responses.

Staphylococcus aureus biofilms: recent developments in biofilm dispersal

Staphylococcus aureus is a major cause of nosocomial and community-acquired infections and represents a significant burden on the healthcare system. S. aureus attachment to medical implants and host tissue, and the establishment of a mature biofilm, play an important role in the persistence of chronic infections. The formation of a biofilm, and encasement of cells in a polymer-based matrix, decreases the susceptibility to antimicrobials and immune defenses, making these infections difficult to eradicate. During infection, dispersal of cells from the biofilm can result in spread to secondary sites and worsening of the infection. In this review, we discuss the current understanding of the pathways behind biofilm dispersal in S. aureus, with a focus on enzymatic and newly described broad-spectrum dispersal mechanisms. Additionally, we explore potential applications of dispersal in the treatment of biofilm-mediated infections.

In vitro photodynamic inactivation effects of Ru(II) complexes on clinical methicillin-resistant Staphylococcus aureus planktonic and biofilm cultures

Photosensitizers (PSs) combined with light are able to generate antimicrobial effects. Ru(II) complexes have been recognized as a novel class of PSs. In this study, we investigated the effectiveness of photodynamic inactivation (PDI) mediated by three Ru(II) polypyridine complexes, 1-3, against four isolates of clinical methicillin-resistant Staphylococcus aureus (MRSA-1, MRSA-2, MRSA-3 and MRSA-4). In PDI of a planktonic culture of MRSA-1, compound 3 showed the highest efficacy, likely owing to its advantageous light absorption, (1) O2 quantum yield and bacterial cellular binding. The PDI efficacy of 3 was further evaluated against all other strains and MRSA-1 biofilms. At appropriate PS concentrations, viability reduction of 100% or 96.83% was observed in planktonic or biofilm forms of MRSA, respectively. The mechanisms of action were investigated using negative staining transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). It was demonstrated that PDI of planktonic bacteria was achieved primarily through damage to the cell envelope. Biofilms were eliminated through both the destruction of their structure and inactivation of the individual bacterial cells. In conclusion, Ru(II) complexes, especially 3, are potential candidates for the effective photodynamic control of MRSA infections.

Polymicrobial synergy and dysbiosis in inflammatory disease

Uncontrolled inflammation of the periodontal area may arise when complex microbial communities transition from a commensal to a pathogenic entity. Communication among constituent species leads to polymicrobial synergy between metabolically compatible organisms that acquire functional specialization within the developing community. Keystone pathogens, even at low abundance, elevate community virulence, and the resulting dysbiotic community targets specific aspects of host immunity to further disable immune surveillance while promoting an overall inflammatory response. Inflammophilic organisms benefit from proteinaceous substrates derived from inflammatory tissue breakdown. Inflammation and dysbiosis reinforce each other, and the escalating environmental changes further select for a pathobiotic community. We have synthesized the polymicrobial synergy and dysbiotic components of the process into a new model for inflammatory diseases.

Prolonged growth of a clinical Staphylococcus aureus strain selects for a stable small-colony-variant cell type

An undetermined feature of Staphylococcus aureus pathogenesis is its persistence and then relapse of disease. This has been explained by its switch to alternative lifestyles, mainly as biofilm or small-colony variants (SCVs). Studying the native characteristics of SCVs has been problematic due to their reversion to the parental lifestyle. We have observed that for a number of S. aureus strains as they switch to an SCV lifestyle, there is the formation of an extracellular matrix. We focused our analysis on one strain, WCH-SK2. For bacterial survival in the host, the combination of low nutrients and the prolonged time frame forms a stress that selects for a specific cell type from the population. In this context, we used steady-state growth conditions with low nutrients and a controlled low growth rate for a prolonged time and with methylglyoxal. These conditions induced S. aureus WCH-SK2 into a stable SCV cell type; the cells did not revert after subculturing. Analysis revealed these cells possessed a metabolic and surface profile that was different from those of previously described SCVs or biofilm cells. The extracellular matrix was protein and extracellular DNA but not polysaccharide. The SCV cells induced expression of certain surface proteins (such as Ebh) and synthesis of lantibiotics while downregulating factors that stimulate the immune response (leucocidin, capsule, and carotenoid). Our data reveal cell heterogeneity within an S. aureus population and under conditions that resemble long-term survival in the host have identified a previously unnoticed S. aureus cell type with a distinctive metabolic and molecular profile.

Biocompatible nanocarrier fortified with a dipyridinium-based amphiphile for eradication of biofilm

Annihilation of bacterial biofilms is challenging owing to their formidable resistance to therapeutic antibiotics and thus there is a constant demand for development of potent antibiofilm agents that can abolish established biofilms. In the present study, the activity of a dipyridinium-based cationic amphiphile (compound 1) against established bacterial biofilms and the subsequent development of a compound 1-loaded nanocarrier for potential antibiofilm therapy are highlighted. Solution-based assays and microscopic analysis revealed the antagonistic effect of compound 1 on biofilms formed by Staphylococcus aureus MTCC 96 and Pseudomonas aeruginosa MTCC 2488. In combination studies, compound 1 could efficiently potentiate the action of tobramycin and gentamicin on P. aeruginosa and S. aureus biofilm, respectively. A human serum albumin (HSA)-based nanocarrier loaded with compound 1 was generated, which exhibited sustained release of compound 1 at physiological pH. The compound 1-loaded HSA nanocarrier (C1-HNC) displayed the signature membrane-directed activity of the amphiphile on target bacteria, efficiently eliminated established bacterial biofilms, and was observed to be nontoxic to a model human cell line. Interestingly, compound 1 as well as the amphiphile-loaded HSA nanocarrier could eradicate established S. aureus biofilm from the surface of a Foley's urinary catheter. On the basis of its biocompatibility and high antibiofilm activity, it is conceived that the amphiphile-loaded nanocarrier may hold potential in antibiofilm therapy.

Identification of lactobacilli with inhibitory effect on biofilm formation by pathogenic bacteria on stainless steel surfaces

Two hundred and thirty individual clones of microorganisms were recovered from milk tanks and milking machine surfaces at two distinct farms (Bejaja City, Algeria). Of these clones, 130 were identified as lactic acid bacteria (LAB). In addition Escherichia coli, Salmonella, Staphylococcus aureus and Pseudomonas aeruginosa species were identified in the remaining 100 isolates-spoilage isolate. These isolates were assayed for ability to form biofilms. S. aureus, Lactobacillus brevis strains LB1F2, LB14F1 and LB15F1, and Lactobacillus pentosus strains LB2F2 and LB3F2 were identified as the best biofilm formers. Besides, these LAB isolates were able to produce proteinaceous substances with antagonism against the aforementioned spoilage isolates, when grown in MRS or TSB-YE media. During the screening, L. pentosus LB3F2 exhibited the highest antibacterial activity when grown in TSB-YE medium at 30 °C. Additionally, L. pentosus LB3F2 was able to strongly hamper the adhesion of S. aureus SA3 on abiotic surfaces as polystyrene and stainless steel slides. LAB isolates did not show any hemolytic activity and all of them were sensitive to different families of antibiotic tested. It should be pointed out that LB3F2 isolate was not cytotoxic on the intestinal cells but could stimulate their metabolic activity. This report unveiled the potential of LB1F2, LB14F1, LB15F1, LB2F2, and LB3F2 isolates to be used as natural barrier or competitive exclusion organism in the food processing sector as well as a positive biofilm forming bacteria.

Discovery of quinoline small molecules with potent dispersal activity against methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis biofilms using a scaffold hopping strategy

Staphylococcus aureus and Staphylococcus epidermidis are recognized as the most frequent cause of biofilm-associated nosocomial and indwelling medical device infections. Biofilm-associated infections are known to be highly resistant to our current arsenal of clinically used antibiotics and antibacterial agents. To exacerbate this problem, no therapeutic option exists that targets biofilm-dependent machinery critical to Staphylococcal biofilm formation and maintenance. Here, we describe the discovery of a series of quinoline small molecules that demonstrate potent biofilm dispersal activity against methicillin-resistant S. aureus and S. epidermidis using a scaffold hopping strategy. This interesting class of quinolines also has select synthetic analogues that demonstrate potent antibacterial activity and biofilm inhibition against S. aureus and S. epidermidis.

Methicillin-resistant Staphylococcus aureus biofilm formation on dacryocystorhinostomy silicone tubes depends on the genetic lineage

PURPOSE

The aim of this study was to investigate biofilm formation on silicone tubes by genetically diverse methicillin-resistant Staphylococcus aureus (MRSA) strains.

METHODS

Capacity of biofilm formation on dacryocystorhinostomy silicone tubes was tested on 30 MRSA strains. Identification and methicillin resistance were confirmed by PCR for nuc and mecA genes. Strains were genotypically characterised (SCCmec, agr and spa typing). Biofilm formation was tested in microtiter plate and on silicone tubes.

RESULTS

Tested MRSA strains were classified into SCCmec type I (33.3%), II (3.3%), III (20.0%), IV (26.7%) and V (16.7%), agr type I (56.7%), II (36.7%) and III (6.6%), and eight spa clonal complexes (CCs). All tested MRSA strains showed ability to form biofilm on microtiter plate. Capacity of biofilm formation on silicone tubes was as follows: 33.3% of strains belonged to the category of low biofilm producers, and 66.7% to moderate biofilm producers. There was statistically significant correlation between spa CC and the category of biofilm production on silicone tubes (p = 0.01): CC5 and CC45 with moderate amount of biofilm, and CC8 with low amount of biofilm. A moderate amount of biofilm formed on silicone tubes correlated with agr type II MRSA strains (p = 0.008).

CONCLUSIONS

Biofilm formation by MRSA on silicone tubes is highly dependent on genetic characteristics of the strains. Therefore, MRSA genotyping may aid the determination of the possibility of biofilm-related ocular device infections. Genotyping and biofilm quantification may be helpful in determining when decolonisation and cohort isolation are required to prevent device-related infections.

A refined technique for extraction of extracellular matrices from bacterial biofilms and its applicability

Biofilm-forming bacteria embedded in polymeric extracellular matrices (ECMs) that consist of polysaccharides, proteins and/or extracellular DNAs (eDNAs) acquire high resistance to antimicrobial agents and host immune systems. To understand molecular mechanisms of biofilm formation and maintenance and to develop therapeutic countermeasures against chronic biofilm-associated infections, reliable methods to isolate ECMs are inevitable. In this study, we refined the ECM extraction method recently reported and evaluated its applicability. Using three Staphylococcus aureus biofilms in which proteins, polysaccharides or eDNAs are major contributors to their integrity, ECMs were extracted using salts and detergents. We found that extraction with 1.5 M sodium chloride (NaCl) could be optimum for not only ECM proteins but also polysaccharides and eDNAs. In addition, long-time incubation was not necessary for efficient ECM isolation. Lithium chloride (LiCl) was comparative to NaCl but is more expensive. In contrast to SDS, NaCl hardly caused leakage of intracellular proteins and did not affect viability of bacterial cells within biofilms. Furthermore, this method is applicable to other bacteria such as Gram-positive Staphylococcus epidermidis and Gram-negative Escherichia coli and Pseudomonas aeruginosa. Thus, this refined method is very simple, rapid, low cost and non-invasive and could be used for a broad range of applications.

How microorganisms use hydrophobicity and what does this mean for human needs?

Cell surface hydrophobicity (CSH) plays a crucial role in the attachment to, or detachment from the surfaces. The influence of CSH on adhesion of microorganisms to biotic and abiotic surfaces in medicine as well as in bioremediation and fermentation industry has both negative and positive aspects. Hydrophobic microorganisms cause the damage of surfaces by biofilm formation; on the other hand, they can readily accumulate on organic pollutants and decompose them. Hydrophilic microorganisms also play a considerable role in removing organic wastes from the environment because of their high resistance to hydrophobic chemicals. Despite the many studies on the environmental and metabolic factors affecting CSH, the knowledge of this subject is still scanty and is in most cases limited to observing the impact of hydrophobicity on adhesion, aggregation or flocculation. The future of research seems to lie in finding a way to managing the microbial adhesion process, perhaps by steering cell hydrophobicity.

Phase variation of poly-N-acetylglucosamine expression in Staphylococcus aureus

Polysaccharide intercellular adhesin (PIA), also known as poly-N-acetyl-β-(1–6)-glucosamine (PIA/PNAG) is an important component of Staphylococcus aureus biofilms and also contributes to resistance to phagocytosis. The proteins IcaA, IcaD, IcaB, and IcaC are encoded within the intercellular adhesin (ica) operon and synthesize PIA/PNAG. We discovered a mechanism of phase variation in PIA/PNAG expression that appears to involve slipped-strand mispairing. The process is reversible and RecA-independent, and involves the expansion and contraction of a simple tetranucleotide tandem repeat within icaC. Inactivation of IcaC results in a PIA/PNAG-negative phenotype. A PIA/PNAG-hyperproducing strain gained a fitness advantage in vitro following the icaC mutation and loss of PIA/PNAG production. The mutation was also detected in two clinical isolates, suggesting that under certain conditions, loss of PIA/PNAG production may be advantageous during infection. There was also a survival advantage for an icaC-negative strain harboring intact icaADB genes relative to an isogenic icaADBC deletion mutant. Together, these results suggest that inactivation of icaC is a mode of phase variation for PIA/PNAG expression, that high-level production of PIA/PNAG carries a fitness cost, and that icaADB may contribute to bacterial fitness, by an unknown mechanism, in the absence of an intact icaC gene and PIA/PNAG production.

Staphylococcal polysaccharide intercellular adhesin (PIA), also known as β-1-6-linked N-acetylglucosamine (PNAG) plays a role in immune evasion and biofilm formation. Evidence suggests that under certain circumstances PIA/PNAG production is beneficial, whereas at times, it may be advantageous for the bacteria to turn production off. In S. epidermidis, PIA/PNAG can be switched off when an insertion sequence recombines into the intercellular adhesin locus (ica). In this study, we have found a short tandem repeat sequence in the ica locus of S. aureus that can undergo expansion and contraction. The addition or subtraction of non-multiples of three of this repeat shifts the reading frame of the icaC gene, resulting in the complete loss of PIA/PNAG production. We hypothesize that certain conditions that make the PIA/PNAG-negative phenotype advantageous during infection, such as the development of an effective immune response to PIA/PNAG on the bacterial surface, would select for repeat mutants. In support of this hypothesis, we found clinical isolates with expansion and deletion of the repeat. These findings reveal a new on-off switch for the expression of PIA/PNAG.

Manuka honey inhibits adhesion and invasion of medically important wound bacteria in vitro

AIM

To characterize the effect of manuka honey on medically important wound bacteria in vitro, focusing on its antiadhesive properties.

MATERIALS & METHODS

Crystal violet biofilm assays, fluorescent microscopy, protein adhesion assay and gentamicin protection assay were used to determine the impact of manuka honey on biofilm formation, human protein binding and adherence to/invasion into human keratinocytes.

RESULTS

Manuka honey effectively disrupted and caused extensive cell death in biofilms of Staphylococcus aureus, Pseudomonas aeruginosa and Streptococcus pyogenes. Sublethal doses of manuka honey inhibited bacterial adhesion to the fibronectin, fibrinogen and collagen. Manuka honey impaired adhesion of laboratory and clinical isolates of S. aureus, P. aeruginosa and S. pyogenes to human keratinocytes in vitro, and inhibited invasion by S. pyogenes and homogeneous vancomycin intermediate S. aureus.

CONCLUSION

Manuka honey can directly affect bacterial cells embedded in a biofilm and exhibits antiadhesive properties against three common wound pathogens.

Mechanistic insights into response of Staphylococcus aureus to bioelectric effect on polypyrrole/chitosan film

Treatment of biofilm-related infections in orthopedics remains a serious clinical challenge. It is known that an electric current can significantly enhance the potency of some antibiotics against biofilms (bioelectric effect) but the uncertainty of the mechanisms and the electrolytic cell-like system used in previous studies limit its applications. Herein, the behavior of Staphylococcus aureus (S. aureus) on an electrically conductive polypyrrole/chitosan film upon passage of a direct current (DC) through the film was investigated in the absence and presence of gentamicin. The killing efficacy of the bacteria within the biofilm by gentamicin was greatly enhanced by the DC treatment. From an analysis of the gene expression by the biofilm bacteria after treatment with gentamicin, DC and their combination, it is postulated that the promotion of bacterial autolysis by DC treatment is responsible for the enhanced susceptibility of biofilm S. aureus to gentamicin. This postulate is supported by an increase in the amount of extracellular deoxyribonucleic acid and adenosine triphosphate, and the appearance of disrupted bacterial cells in the biofilm after DC treatment. These findings provide a new insight into the interaction between DC and bacteria, and offer potential benefits for the treatment of infections in orthopedics.

Impact of the functional status of saeRS on in vivo phenotypes of Staphylococcus aureus sarA mutants

We investigated the in vivo relevance of the impact of sarA and saeRS on protease production using derivatives of the USA300 strain LAC. The results confirmed that mutation of saeRS or sarA reduces virulence in a bacteremia model to a comparable degree. However, while eliminating protease production restored virulence in the sarA mutant, it had little impact in the saeRS mutant. Additionally, constitutive activation of saeRS (saeRS(C)) enhanced the virulence of LAC and largely restored virulence in the isogenic sarA mutant. Based on these results, together with our analysis of the representative virulence factors alpha toxin, protein A (Spa), and extracellular nucleases, we propose a model in which the attenuation of saeRS mutants is defined primarily by decreased production of such factors, while constitutive activation of saeRS increases virulence, and reverses the attenuation of sarA mutants, because it results in both increased production and decreased protease-mediated degradation of these same factors. This regulatory balance was also apparent in a murine model of catheter-associated infection, with the results suggesting that the impact of saeRS on nuclease production plays an important role during the early stages of these infections that is partially offset by increased protease production in sarA mutants.

Antibiofilm Effect of Octenidine Hydrochloride on Staphylococcus aureus, MRSA and VRSA

Millions of indwelling devices are implanted in patients every year, and staphylococci (S. aureus, MRSA and vancomycin-resistant S. aureus (VRSA)) are responsible for a majority of infections associated with these devices, thereby leading to treatment failures. Once established, staphylococcal biofilms become resistant to antimicrobial treatment and host response, thereby serving as the etiological agent for recurrent infections. This study investigated the efficacy of octenidine hydrochloride (OH) for inhibiting biofilm synthesis and inactivating fully-formed staphylococcal biofilm on different matrices in the presence and absence of serum protein. Polystyrene plates and stainless steel coupons inoculated with S. aureus, MRSA or VRSA were treated with OH (zero, 0.5, one, 2 mM) at 37 °C for the prevention of biofilm formation. Additionally, the antibiofilm effect of OH (zero, 2.5, five, 10 mM) on fully-formed staphylococcal biofilms on polystyrene plates, stainless steel coupons and urinary catheters was investigated. OH was effective in rapidly inactivating planktonic and biofilm cells of S. aureus, MRSA and VRSA on polystyrene plates, stainless steel coupons and urinary catheters in the presence and absence of serum proteins. The use of two and 10 mM OH completely inactivated S. aureus planktonic cells and biofilm (>6.0 log reduction) on all matrices tested immediately upon exposure. Further, confocal imaging revealed the presence of dead cells and loss in biofilm architecture in the OH-treated samples when compared to intact live biofilm in the control. Results suggest that OH could be applied as an effective antimicrobial to control biofilms of S. aureus, MRSA and VRSA on appropriate hospital surfaces and indwelling devices.

Quorum sensing-mediated regulation of staphylococcal virulence and antibiotic resistance

ABSTRACT: 

Accessory gene regulator (agr)-mediated quorum sensing plays a central role in staphylococcal pathogenesis. It primarily upregulates secreted virulence factors and downregulates cell surface proteins, thereby governing invasiveness of staphylococci and cell dispersal from biofilms. Except for α- and β-PSMs, which are directly controlled by AgrA, the effector functions of agr are primarily mediated by RNAIII, a regulatory RNA encoded by this operon. agr phenotype and expression considerably influence the chronicity of an infection. It has also been linked with altered susceptibility of Staphylococcus aureus against antibiotics. Four classes of S. aureus and Staphylococcus epidermidis AIPs exist based on sequence variation, and lead to inter-strain and species cross-inhibition. Certain agr classes have been associated with specific clonal complexes, disease syndromes and intermediate-susceptibility to glycopeptides. It is also being investigated as a prophylactic and therapeutic target. This article describes the presently available literature regarding the role of agr in S. aureus and S. epidermidis infections.

Structure-function analysis of Staphylococcus aureus amidase reveals the determinants of peptidoglycan recognition and cleavage

The bifunctional major autolysin AtlA of Staphylococcus aureus cleaves the bacterium's peptidoglycan network (PGN) at two distinct sites during cell division. Deletion of the enzyme results in large cell clusters with disordered division patterns, indicating that AtlA could be a promising target for the development of new antibiotics. One of the two functions of AtlA is performed by the N-acetylmuramyl-l-alanine amidase AmiA, which cleaves the bond between the carbohydrate and the peptide moieties of PGN. To establish the structural requirements of PGN recognition and the enzymatic mechanism of cleavage, we solved the crystal structure of the catalytic domain of AmiA (AmiA-cat) in complex with a peptidoglycan-derived ligand at 1.55 Å resolution. The peptide stem is clearly visible in the structure, forming extensive contacts with protein residues by docking into an elongated groove. Less well defined electron density and the analysis of surface features indicate likely positions of the carbohydrate backbone and the pentaglycine bridge. Substrate specificity analysis supports the importance of the pentaglycine bridge for fitting into the binding cleft of AmiA-cat. PGN of S. aureus with l-lysine tethered with d-alanine via a pentaglycine bridge is completely hydrolyzed, whereas PGN of Bacillus subtilis with meso-diaminopimelic acid directly tethered with d-alanine is not hydrolyzed. An active site mutant, H370A, of AmiA-cat was completely inactive, providing further support for the proposed catalytic mechanism of AmiA. The structure reported here is not only the first of any bacterial amidase in which both the PGN component and the water molecule that carries out the nucleophilic attack on the carbonyl carbon of the scissile bond are present; it is also the first peptidoglycan amidase complex structure of an important human pathogen.

Hiding in Plain Sight: Interplay between Staphylococcal Biofilms and Host Immunity

Staphylococcus aureus and Staphylococcus epidermidis are notable for their propensity to form biofilms on implanted medical devices. Staphylococcal biofilm infections are typified by their recalcitrance to antibiotics and ability to circumvent host immune-mediated clearance, resulting in the establishment of chronic infections that are often recurrent in nature. Indeed, the immunomodulatory lifestyle of biofilms seemingly shapes the host immune response to ensure biofilm engraftment and persistence in an immune competent host. Here, we provide a brief review of the mechanisms whereby S. aureus and S. epidermidis biofilms manipulate host–pathogen interactions and discuss the concept of microenvironment maintenance in infectious outcomes, as well as speculate how these findings pertain to the challenges of staphylococcal vaccine development.

Staphylococcus aureus persistence in non-professional phagocytes

S. aureus is a frequent cause of chronic and therapy-refractory infections. The ability of S. aureus to invade different types of non-professional phagocytes, to escape from the host lysosomal degradation machinery and to persist within the intracellular location for long time periods are most likely essential steps in pathogenesis. During the course from acute to chronic infection the bacteria need to dynamically react to the environmental changes and to adapt to the intracellular environment. In this context the bacteria change to SCV-like phenotypes that exhibit some characteristics of stable SCV-mutants, like upregulation of adhesins and downregulation of toxins. The exact formation mechanism and further typical features of these dynamically forming SCVs are largely unknown. In this review, recent data on the essential steps to establish chronic infections will be summarized and the clinical consequences of the dynamic bacterial adaptation mechanisms will be discussed.

Direct and indirect antimicrobial activities of neuropeptides and their therapeutic potential

As global resistance to conventional antibiotics rises we need to develop new strategies to develop future novel therapeutics. In our quest to design novel anti-infectives and antimicrobials it is of interest to investigate host-pathogen interactions and learn from the complexity of host defense strategies that have evolved over millennia. A myriad of host defense molecules are now known to play a role in protection against human infection. However, the interaction between host and pathogen is recognized to be a multifaceted one, involving countless host proteins, including several families of peptides. The regulation of infection and inflammation by multiple peptide families may represent an evolutionary failsafe in terms of functional degeneracy and emphasizes the significance of host defense in survival. One such family is the neuropeptides (NPs), which are conventionally defined as peptide neurotransmitters but have recently been shown to be pleiotropic molecules that are integral components of the nervous and immune systems. In this review we address the antimicrobial and anti-infective effects of NPs both in vitro and in vivo and discuss their potential therapeutic usefulness in overcoming infectious diseases. With improved understanding of the efficacy of NPs, these molecules could become an important part of our arsenal of weapons in the treatment of infection and inflammation. It is envisaged that targeted therapy approaches that selectively exploit the anti-infective, antimicrobial and immunomodulatory properties of NPs could become useful adjuncts to our current therapeutic modalities.

Staphylococcus aureus biofilm activates the nucleotide-binding oligomerization domain containing 2 (Nod2) pathway and proinflammatory factors on a human sinonasal explant model

BACKGROUND

The presence of Staphylococcus aureus biofilms on sinonasal mucosal surfaces is associated with recalcitrant chronic rhinosinusitis (CRS), but little is known about the innate immune response they trigger. We aimed to study the human pattern recognition receptor (PRR) nucleotide-binding oligomerization domain containing 2 (Nod2) receptor and downstream pathway in response to initial S. aureus biofilm infection.

METHODS

Using a validated protocol, sinonasal mucosae from 4 non-CRS donors were cultured with and without S. aureus biofilms and planktonic cells. After 24 hours, RNA was extracted and gene expression was analyzed using a human antibacterial response polymerase chain reaction (PCR) array. Immunohistochemistry was performed to confirm the presence and determine the immunolocalization of selected proteins.

RESULTS

C-X-C motif (CXC) chemokine ligands 1 and 2, interleukin-6 (IL-6), and genes related to the Nod2 pathway were significantly upregulated in biofilm-treated tissues compared with control samples. Nod2 pathway-specific gene expression was increased in biofilm-treated tissues compared with planktonic S. aureus-treated explants. Enhanced expression of Nod2 and nuclear factor kappa B1 (NF-κB1) was also detected with immunohistochemistry in control and biofilm-treated tissues.

CONCLUSION

S. aureus biofilms exerted a proinflammatory response in the mucosa and activation of the Nod2 pathway, indicating this receptor to be involved in the innate immune response to S. aureus biofilms. Further studies are required to elucidate the role of this pathway in CRS.

Secreted proteases control autolysin-mediated biofilm growth of Staphylococcus aureus

Staphylococcus epidermidis, a commensal of humans, secretes Esp protease to prevent Staphylococcus aureus biofilm formation and colonization. Blocking S. aureus colonization may reduce the incidence of invasive infectious diseases; however, the mechanism whereby Esp disrupts biofilms is unknown. We show here that Esp cleaves autolysin (Atl)-derived murein hydrolases and prevents staphylococcal release of DNA, which serves as extracellular matrix in biofilms. The three-dimensional structure of Esp was revealed by x-ray crystallography and shown to be highly similar to that of S. aureus V8 (SspA). Both atl and sspA are necessary for biofilm formation, and purified SspA cleaves Atl-derived murein hydrolases. Thus, S. aureus biofilms are formed via the controlled secretion and proteolysis of autolysin, and this developmental program appears to be perturbed by the Esp protease of S. epidermidis.

Vesicle formation as a result of interaction between polymorphonuclear neutrophils and Staphylococcus aureus biofilm

Staphylococcus aureus, a major opportunistic pathogen, is a leading cause of biofilm-related infections in clinical practice. Staphylococcal biofilms are highly resistant to antibacterial medicines and immune effector cells. The main result of our work is the discovery of nano-vesicles in the supernatant of the human neutrophil–S. aureus biofilm system. We also found that phospholipase C treatment causes complete destruction of these vesicles. While the addition of proteinase K led to a partial structural disorganization of the vesicles, DNase treatment did not influence the vesicle structure. These observations allowed us to conclude that phospholipids and proteins play a structure-forming role in the formation of these nano-vesicles. The vesicles demonstrated anti-biofilm activities when tested against Staphylococcus epidermidis (strains 178M and 328/5) biofilms, but were ineffective for S. aureus (strains 5983/2, 5663 and 18A) biofilms.

Staphopains modulate Staphylococcus aureus biofilm integrity

Staphylococcus aureus is a known cause of chronic biofilm infections that can reside on medical implants or host tissue. Recent studies have demonstrated an important role for proteinaceous material in the biofilm structure. The S. aureus genome encodes many secreted proteases, and there is growing evidence that these enzymes have self-cleavage properties that alter biofilm integrity. However, the specific contribution of each protease and mechanism of biofilm modulation is not clear. To address this issue, we utilized a sigma factor B (ΔsigB) mutant where protease activity results in a biofilm-negative phenotype, thereby creating a condition where the protease(s) responsible for the phenotype could be identified. Using a plasma-coated microtiter assay, biofilm formation was restored to the ΔsigB mutant through the addition of the cysteine protease inhibitor E-64 or by using Staphostatin inhibitors that specifically target the extracellular cysteine proteases SspB and ScpA (called Staphopains). Through construction of gene deletion mutants, we determined that an sspB scpA double mutant restored ΔsigB biofilm formation, and this recovery could be replicated in plasma-coated flow cell biofilms. Staphopain levels were also found to be decreased under biofilm-forming conditions, possibly allowing biofilm establishment. The treatment of S. aureus biofilms with purified SspB or ScpA enzyme inhibited their formation, and ScpA was also able to disperse an established biofilm. The antibiofilm properties of ScpA were conserved across S. aureus strain lineages. These findings suggest an underappreciated role of the SspB and ScpA cysteine proteases in modulating S. aureus biofilm architecture.

Alcohol treatment enhances Staphylococcus aureus biofilm development

Staphylococcus aureus forms pathogenic biofilms. Previous studies have indicated that ethanol supplementation during S. aureus biofilm formation results in increased biofilm formation and changes in gene expression. However, the impact of alcohols on preformed S. aureus biofilms has not been studied. In this study, we formed S. aureus biofilms on PVC plastic plates and then treated these preformed biofilms with five different alcohols. We observed that alcohol treatment of preformed S. aureus biofilms led to significant increases in biofilm levels after 24 h of treatment. Many bacteria within these biofilms were found to be alive and metabolically active. Alcohol treatment also resulted in increased transcription of the biofilm-promoting genes icaA and icaD, as well as several antibiotic resistance genes. These results demonstrate that treatment of S. aureus preformed biofilms with alcohols enhances biofilm levels if maintained for extended periods. Thus, alcohols might be of limited usefulness for the eradication of preformed S. aureus biofilms.

SigB is a dominant regulator of virulence in Staphylococcus aureus small-colony variants

Staphylococcus aureus small-colony variants (SCVs) are persistent pathogenic bacteria characterized by slow growth and, for many of these strains, an increased ability to form biofilms and to persist within host cells. The virulence-associated gene expression profile of SCVs clearly differs from that of prototypical strains and is often influenced by SigB rather than by the agr system. One objective of this work was to confirm the role of SigB in the control of the expression of virulence factors involved in biofilm formation and intracellular persistence of SCVs. This study shows that extracellular proteins are involved in the formation of biofilm by three SCV strains, which, additionally, have a low biofilm-dispersing activity. It was determined that SigB activity modulates biofilm formation by strain SCV CF07-S and is dominant over that of the agr system without being solely responsible for the repression of proteolytic activity. On the other hand, the expression of fnbA and the control of nuclease activity contributed to the SigB-dependent formation of biofilm of this SCV strain. SigB was also required for the replication of CF07-S within epithelial cells and may be involved in the colonization of lungs by SCVs in a mouse infection model. This study methodically investigated SigB activity and associated mechanisms in the various aspects of SCV pathogenesis. Results confirm that SigB activity importantly influences the production of virulence factors, biofilm formation and intracellular persistence for some clinical SCV strains.

Keto-mycolic acid-dependent pellicle formation confers tolerance to drug-sensitive Mycobacterium tuberculosis

The chronic nature of tuberculosis (TB), its requirement of long duration of treatment, its ability to evade immune intervention, and its propensity to relapse after drug treatment is discontinued are reminiscent of other chronic, biofilm-associated bacterial diseases. Historically, Mycobacterium tuberculosis was grown as a pellicle, a biofilm-like structure, at the liquid-air interface in a variety of synthetic media. Notably, the most widely administered human vaccine, BCG, is grown as a pellicle for vaccine production. However, the molecular requirements for this growth remain ill defined. Here, we demonstrate that keto-mycolic acids (keto-MA) are essential for pellicle growth, and mutants lacking in or depleted of this MA species are unable to form a pellicle. We investigated the role of the pellicle biofilm in the reduction of antibiotic sensitivity known as drug tolerance using the pellicle-defective ΔmmaA4 mutant strain. We discovered that the ΔmmaA4 mutant, which is both pellicle defective and highly sensitive to rifampicin (RIF) under planktonic growth, when incorporated within the wild-type pellicle biofilm, was protected from the bactericidal activity of RIF. The observation that growth within the M. tuberculosis pellicle biofilm can confer drug tolerance to a drug-hypersensitive strain suggests that identifying molecular requirements for pellicle growth could lead to development of novel interventions against mycobacterial infections. Our findings also suggest that a class of drugs that can disrupt M. tuberculosis biofilm formation, when used in conjunction with conventional antibiotics, has the potential to overcome drug tolerance.

Two of the most important questions in tuberculosis (TB) research are (i) how does Mycobacterium tuberculosis persist in the human host for decades in the face of an active immune response and (ii) why does it take six months and four drugs to treat uncomplicated TB. Both these aspects of M. tuberculosis biology are reminiscent of infections caused by organisms capable of forming biofilms. M. tuberculosis is capable of growing as a biofilm-like structure called the pellicle. In this study, we demonstrate that a specific cell wall component, keto-mycolic acid, is essential for pellicle growth. We also demonstrate that a strain of M. tuberculosis that is both drug sensitive and pellicle defective exhibits commensal behavior and becomes drug tolerant by becoming part of a heterogeneous pellicle, a characteristic of multispecies biofilms. These observations could have important implications for identifying novel pathways for M. tuberculosis drug tolerance and the design of new modalities to rapidly treat TB.

Antimicrobial surfaces for craniofacial implants: state of the art

In an attempt to regain function and aesthetics in the craniofacial region, different biomaterials, including titanium, hydroxyapatite, biodegradable polymers and composites, have been widely used as a result of the loss of craniofacial bone. Although these materials presented favorable success rates, osseointegration and antibacterial properties are often hard to achieve. Although bone-implant interactions are highly dependent on the implant's surface characteristics, infections following traumatic craniofacial injuries are common. As such, poor osseointegration and infections are two of the many causes of implant failure. Further, as increasingly complex dental repairs are attempted, the likelihood of infection in these implants has also been on the rise. For these reasons, the treatment of craniofacial bone defects and dental repairs for long-term success remains a challenge. Various approaches to reduce the rate of infection and improve osseointegration have been investigated. Furthermore, recent and planned tissue engineering developments are aimed at improving the implants' physical and biological properties by improving their surfaces in order to develop craniofacial bone substitutes that will restore, maintain and improve tissue function. In this review, the commonly used biomaterials for craniofacial bone restoration and dental repair, as well as surface modification techniques, antibacterial surfaces and coatings are discussed.

The staphylococcal enterotoxin (SE) family: SEB and siblings

Staphylococcus aureus plays an important role in numerous human cases of food poisoning, soft tissue, and bone infections, as well as potentially lethal toxic shock. This common bacterium synthesizes various virulence factors that include staphylococcal enterotoxins (SEs). These protein toxins bind directly to major histocompatibility complex class II on antigen-presenting cells and specific Vβ regions of T-cell receptors, resulting in potentially life-threatening stimulation of the immune system. Picomolar concentrations of SEs ultimately elicit proinflammatory cytokines that can induce fever, hypotension, multi-organ failure, and lethal shock. Various in vitro and in vivo models have provided important tools for studying the biological effects of, as well as potential vaccines/therapeutics against, the SEs. This review succinctly presents known physical and biological properties of the SEs, including various intervention strategies. In particular, SEB will often be portrayed as per biodefense concerns dating back to the 1960s.

A combined pharmacodynamic quantitative and qualitative model reveals the potent activity of daptomycin and delafloxacin against Staphylococcus aureus biofilms

Biofilms are associated with persistence of Staphylococcus aureus infections and therapeutic failures. Our aim was to set up a pharmacodynamic model comparing antibiotic activities against biofilms and examining in parallel their effects on viability and biofilm mass. Biofilms of S. aureus ATCC 25923 (methicillin-sensitive S. aureus [MSSA]) or ATCC 33591 (methicillin-resistant S. aureus [MRSA]) were obtained by culture in 96-well plates for 6 h/24 h. Antibiotic activities were assessed after 24/48 h of exposure to concentrations ranging from 0.5 to 512 times the MIC. Biofilm mass and bacterial viability were quantified using crystal violet and the redox indicator resazurin. Biofilms stained with Live/Dead probes were observed by using confocal microscopy. Concentration-effect curves fitted sigmoidal regressions, with a 50% reduction toward both matrix and viability obtained at sub-MIC or low multiples of MICs against young biofilms for all antibiotics tested. Against mature biofilms, maximal efficacies and potencies were reduced, with none of the antibiotics being able to completely destroy the matrix. Delafloxacin and daptomycin were the most potent, reducing viability by more than 50% at clinically achievable concentrations against both strains, as well as reducing biofilm depth, as observed in confocal microscopy. Rifampin, tigecycline, and moxifloxacin were effective against mature MRSA biofilms, while oxacillin demonstrated activity against MSSA. Fusidic acid, vancomycin, and linezolid were less potent overall. Antibiotic activity depends on biofilm maturity and bacterial strain. The pharmacodynamic model developed allows ranking of antibiotics with respect to efficacy and potency at clinically achievable concentrations and highlights the potential utility of daptomycin and delafloxacin for the treatment of biofilm-related infections.

The role of staphylothrombin-mediated fibrin deposition in catheter-related Staphylococcus aureus infections

Staphylococcus aureus (S. aureus) is a frequent cause of catheter-related infections. S. aureus secretes the coagulases staphylocoagulase and von Willebrand factor-binding protein, both of which form a staphylothrombin complex upon binding to prothrombin. Although fibrinogen and fibrin facilitate the adhesion of S. aureus to catheters, the contribution of staphylothrombin-mediated fibrin has not been examined. In this study, we use a S. aureus mutant lacking both coagulases (Δcoa/vwb) and dabigatran, a pharmacological inhibitor of both staphylothrombin and thrombin, to address this question. Genetic absence or chemical inhibition of pathogen-driven coagulation reduced both fibrin deposition and the retention of S. aureus on catheters in vitro. In a mouse model of jugular vein catheter infection, dabigatran reduced bacterial load on jugular vein catheters, as well as metastatic kidney infection. Importantly, inhibition of staphylothrombin improved the efficacy of vancomycin treatment both in vitro and in the mouse model.

Combined treatments of enterocin AS-48 with biocides to improve the inactivation of methicillin-sensitive and methicillin-resistant Staphylococcus aureus planktonic and sessile cells

Control of staphylococci during cleaning and disinfection is important to the food industry. Broad-spectrum bacteriocins with proved anti-staphylococcal activity, such as enterocin AS-48, could open new possibilities for disinfection in combination with biocides. In the present study, enterocin AS-48 was tested singly or in combination with biocides against a cocktail of six Staphylococcus aureus strains (including three methicillin-resistant strains) in planktonic state as well as in biofilms formed on polystyrene microtiter plates. Cells were challenged with enterocin, biocides or enterocin/biocide combinations. Inactivation of planktonic cells increased significantly (p<0.05) when enterocin AS-48 (25mg/l) was tested in combination with benzalkonium chloride (BC), cetrimide (CT) and hexadecylpyridinium chloride (HDP), and non-significantly in combination with didecyldimethylammonium bromide (AB), triclosan (TC), hexachlorophene (CF), polyhexamethylen guanidinium chloride (PHMG), chlorhexidine (CH) or P3-oxonia (OX). In the sessile state (24h biofilms), staphylococci required higher biocide concentrations in most cases, except for OX. Inactivation of sessile staphylococci increased remarkably when biocides were applied in combination with enterocin AS-48, especially when the bacteriocin was added at 50mg/l. During storage, the concentrations of sessile as well as planktonic cells in the treated samples decreased remarkably for BC, TC and PHMG, but OX failed to inhibit proliferation of the treated biofilms as well as growth of planktonic cells. The observed inhibitory effects during storage were potentiated when the biocides were combined with 50 mg/l enterocin AS-48. Results from this study suggest that selected combinations of enterocin AS-48 and biocides offer potential use against planktonic and sessile, methicillin-sensitive and methicillin-resistant S. aureus.

A human nasal explant model to study Staphylococcus aureus biofilm in vitro

BACKGROUND

Staphylococcus aureus (S. aureus) biofilm has been associated with severe and recalcitrant cases of chronic rhinosinusitis (CRS). However, its role in the pathophysiology of this condition is not completely understood. This study aims to develop a sinonasal tissue explant model to analyze the interaction of S. aureus biofilm with the mucosa in vitro.

METHODS

Sinonasal tissue samples from 5 control patients undergoing pituitary surgery were cultured with and without S. aureus biofilm in vitro. Confocal scanning laser microscopy (CSLM) using the Live/Dead BacLight stain and histology were performed on the tissue explants after 24 hours of biofilm challenge. Measurements of IL-6, at both the messenger RNA (mRNA) level (using quantitative reverse-transcriptase polymerase chain reaction [qRT-PCR]) and the protein level (using enzyme-linked immunosorbent assay [ELISA]), were undertaken to evaluate biofilm-mucosa interaction.

RESULTS

Viability of the explants after 24 hours was confirmed by CSLM and histology. Although light microscopy failed to identify S. aureus biofilms, its presence was confirmed in the biofilm-challenged samples by CSLM. IL-6 mRNA transcript levels were 4.9-fold upregulated in biofilm-treated tissue compared to controls (p = 0.0485). A similar trend was observed at the protein level (p = 0.0313).

CONCLUSION

The sinonasal tissue explant is a viable and functional model capable of analyzing direct biofilm-mucosal interactions and can advance our understanding of the role played by S. aureus biofilm in sinus inflammation. Our model suggests that S. aureus biofilms in the initial phase of growth are not inert bystanders but elicit an immune response in the sinonasal mucosa.

Methods to identify enzymes that degrade the main extracellular polysaccharide component of Staphylococcus epidermidis biofilms

The production of extracellular poly-β-1,6-N-acetyl-d-glucosamine (PNAG) by Staphylococcus epidermidis is the principal determinant of biofilm formation on indwelling medical devices. Enzymes that degrade PNAG therefore provide an attractive strategy for biofilm removal and for the manufacture of biofilm-resistant coatings. Here we present methods that allow the identification of PNAG-degrading enzymes with the ability to detach biofilms. Our protocol includes the preparation of soluble PNAG from S. epidermidis cultures, the incubation of soluble PNAG with candidate enzymes and assays that detect the release of N-acetyl-d-glucosamine using high-pH anion-exchange chromatography (HPAEC) followed in parallel by pulsed amperometric detection (PAD) and online electrospray ionization mass spectrometry (ESI-MS). We validated our procedures using dispersin B, which is currently the only known PNAG-degrading enzyme.