Molecular Genetics of Staphylococcus Epidermidis Biofilms on Indwelling Medical Devices

Targeting bacterial growth in biofilm conditions: rational design of novel inhibitors to mitigate clinical and food contamination using QSAR

Antimicrobial resistance (AMR) is a pressing global issue exacerbated by the abuse of antibiotics and the formation of bacterial biofilms, which cause up to 80% of human bacterial infections. This study presents a computational strategy to address AMR by developing three novel quantitative structure-activity relationship (QSAR) models based on molecular topology to identify potential anti-biofilm and antibacterial agents. The models aim to determine the chemo-topological pattern of Gram (+) antibacterial, Gram (-) antibacterial, and biofilm formation inhibition activity. The models were applied to the virtual screening of a commercial chemical database, resulting in the selection of 58 compounds. Subsequent in vitro assays showed that three of these compounds exhibited the most promising antibacterial activity, with potential applications in enhancing food and medical device safety.

Inhibition of Staphylococcus aureus biofilm formation by gurmarin, a plant-derived cyclic peptide

Staphylococcus aureus (Sa) is an opportunistic pathogen capable of causing various infections ranging from superficial skin infections to life-threatening severe diseases including pneumonia and sepsis. Sa produces biofilms readily on biotic and abiotic surfaces. Biofilm cells are embedded in a protective polysaccharide matrix and show an innate resistance to antibiotics, disinfectants, and clearance by host defenses. Additionally, biofilms serve as a source for systemic dissemination. Moreover, infections associated with biofilms may result in longer hospitalizations, a need for surgery, and may even result in death. Agents that inhibit the formation of biofilms and virulence without affecting bacterial growth to avoid the development of drug resistance could be useful for therapeutic purposes. In this regard, we identified and purified a small cyclic peptide, gurmarin, from a plant source that inhibited the formation of Sa biofilm under in vitro growth conditions without affecting the viability of the bacterium. The purified peptide showed a predicted molecular size of ~4.2 kDa on SDS-PAGE. Transcriptomic analysis of Sa biofilm treated with peptide showed 161 differentially affected genes at a 2-fold change, and some of them include upregulation of genes involved in oxidoreductases and downregulation of genes involved in transferases and hydrolases. To determine the inhibitory effect of the peptide against Sa biofilm formation and virulence in vivo, we used a rat-implant biofilm model. Sa infected implants with or without peptide were placed under the neck skin of rats for seven days. Implants treated with peptide showed a reduction of CFU and lack of edema and sepsis when compared to that of control animals without peptide. Taken together, gurmarin peptide blocks Sa biofilm formation in vitro and in vivo and can be further developed for therapeutic use.

Staphylococcal Biofilm on the Surface of Catheters: Electron Microscopy Evaluation of the Inhibition of Biofilm Growth by RNAIII Inhibiting Peptide

Staphylococcus aureus and coagulase-negative staphylococci (CoNS) have become the main causative agents of medical device-related infections due to their biofilm-forming capability, which protects them from the host’s immune system and from the action of antimicrobials. This study evaluated the ability of RNA III inhibiting peptide (RIP) to inhibit biofilm formation in 10 strains isolated from clinical materials, including one S. aureus strain, two S. epidermidis, two S. haemolyticus, two S. lugdunensis, and one isolate each of the following species: S. warneri, S. hominis, and S. saprophyticus. The isolates were selected from a total of 200 strains evaluated regarding phenotypic biofilm production and the presence and expression of the ica operon. The isolates were cultured in trypticase soy broth with 2% glucose in 96-well polystyrene plates containing catheter segments in the presence and absence of RIP. The catheter segments were observed by scanning electron microscopy. The results showed inhibition of biofilm formation in the presence of RIP in all CoNS isolates; however, RIP did not interfere with biofilm formation by S. aureus. RIP is a promising tool that might be used in the future for the prevention of biofilm-related infections caused by CoNS.

Quercetin Inhibits Biofilm Formation by Decreasing the Production of EPS and Altering the Composition of EPS in Staphylococcus epidermidis

Staphylococcus epidermidis is an opportunistic pathogen, and its biofilm formation ability is an important virulent factor. Quercetin, a typical flavonoid ubiquitously used in dietary supplementation, is known for its antioxidant property, but its anti-biofilm activity against S. epidermidis remains unknown. In this study, the anti-biofilm activity of quercetin was investigated using S. epidermidis ATCC35984, a strong biofilm-positive strain. An attempt was made to disclose the mechanisms of the anti-biofilm activity of quercetin. S. epidermidis exhibited a less cell surface hydrophobicity after quercetin treatment. Also, quercetin effectively inhibited S. epidermidis cells from adhering to the glass slides. Quercetin downregulated the intercellular adhesion (ica) locus and then polysaccharide intercellular adhesin (PIA) production was reduced. Therefore, S. epidermidis cells became less hydrophobic, which supported quercetin’s anti-biofilm effect. Our study suggests that quercetin from plants be given further attention as a potential anti-biofilm agent against the biofilm formation of S. epidermidis, even biofilm infections of other bacteria.

Oxytropis glabra DC. Inhibits Biofilm Formation of Staphylococcus epidermidis by Down-Regulating ica Operon Expression

Staphylococcus epidermidis is one of the main causes of medical device-related infections and bovine mastitis owing to its biofilm-forming abilities. Oxytropis glabra DC. is one of the most widespread Fabaceae species and used as a Chinese herbal formulation in Western China. Our research investigated the effects of O. glabra on the biofilm formation of S. epidermidis and the possible inhibiting mechanism. The biofilm-forming reference strain, S. epidermidis SE-1 (ATCC 35,984), was employed as a model and semi-quantitative biofilm assay was performed to evaluate the antibiofilm activity of O. glabra. The exopolysaccharides (EPS) production and expression of ica operon were studied to explore the possible antibiofilm mechanism using thin-layer chromatography and quantitative real-time PCR assay, respectively. The results obtained indicated that O. glabra decoction at 7.5 mg mL-1 significantly inhibited biofilm formation by about 95% without affecting cell growth of S. epidermidis. Two hydrolysis productions of EPS were significantly decreased by 64% and 54% with the addition of 7.5 mg mL-1O. glabra and the expression of icaR was significantly up-regulated 2.2-times, whereas icaB was significantly down-regulated more than 50% by 7.5 mg mL-1O. glabra. These findings suggest a potential application for O. glabra as a promising candidate for the exploration of new drugs against S. epidermidis biofilm-associated infections.

Streptomyces-derived actinomycin D inhibits biofilm formation via downregulating ica locus and decreasing production of PIA in Staphylococcus epidermidis

AIM

The objective of this study was to investigate the biofilm inhibitory activity of Streptomyces-derived actinomycin D against biofilm formation by Staphylococcus epidermidis.

METHODS AND RESULTS

The microtitre plate method and microscopy were used to detect the biofilm formation of S. epidermidis. And an attempt was made to detect the effect of actinomycin D on important biofilm components, exopolysaccharides (EPS) in S. epidermidis using precolumn derivation HPLC. Also cell surface hydrophobicities of S. epidermidis were assessed to explore action mechanisms. The qPCR was performed to demonstrate the genetic mechanisms of biofilm formation by S. epidermidis. Unlike other antibiotics, actinomycin D (1·5 μg ml^-1 ) from Streptomyces luteus significantly inhibited biofilm formation by S. epidermidis. Additionally, it effectively inhibited S. epidermidis cells from adhering to glass slides. Actinomycin D downregulated ica locus and then the reduced polysaccharide intercellular adhesin production caused S. epidermidis cells to become less hydrophobic, thus supporting its anti-biofilm effect.

CONCLUSION

Streptomyces-derived actinomycin D is active in inhibiting the biofilm formation of S. epidermidis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Actinomycin D can be used as a promising antibiofilm agent in inhibiting S. epidermidis biofilm formation. The study is also the first insight into how actinomycin D inhibited the biofilm formation of S. epidermidis. Actinomycin D could potentially be used to reduce the risk of biofilm-associated infections. Our study also suggests that the metabolites from Actinomycete strains keep further attention as potential antibiofilm agents against biofilm formation of S. epidermidis, even biofilm infections of the other bacteria.

Medical-Grade Silicone Coated with Rhamnolipid R89 Is Effective against Staphylococcus spp. Biofilms

Staphylococcus aureus and Staphylococcus epidermidis are considered two of the most important pathogens, and their biofilms frequently cause device-associated infections. Microbial biosurfactants recently emerged as a new generation of anti-adhesive and anti-biofilm agents for coating implantable devices to preserve biocompatibility. In this study, R89 biosurfactant (R89BS) was evaluated as an anti-biofilm coating on medical-grade silicone. R89BS is composed of homologues of the mono- (75%) and di-rhamnolipid (25%) families, as evidenced by mass spectrometry analysis. The antimicrobial activity against Staphylococcus spp. planktonic and sessile cells was evaluated by microdilution and metabolic activity assays. R89BS inhibited S. aureus and S. epidermidis growth with minimal inhibitory concentrations (MIC₉₉) of 0.06 and 0.12 mg/mL, respectively and dispersed their pre-formed biofilms up to 93%. Silicone elastomeric discs (SEDs) coated by R89BS simple adsorption significantly counteracted Staphylococcus spp. biofilm formation, in terms of both built-up biomass (up to 60% inhibition at 72 h) and cell metabolic activity (up to 68% inhibition at 72 h). SEM analysis revealed significant inhibition of the amount of biofilm-covered surface. No cytotoxic effect on eukaryotic cells was detected at concentrations up to 0.2 mg/mL. R89BS-coated SEDs satisfy biocompatibility requirements for leaching products. Results indicate that rhamnolipid coatings are effective anti-biofilm treatments and represent a promising strategy for the prevention of infection associated with implantable devices.

Selective Inactivation of Pseudomonas aeruginosa and Staphylococcus epidermidis with Pulsed Electric Fields and Antibiotics

Objective: Increasing numbers of multidrug-resistant bacteria make many antibiotics ineffective; therefore, new approaches to combat microbial infections are needed. In addition, antibiotics are not selective-they kill pathogenic organisms as well as organisms that could positively contribute to wound healing (bio flora). Approach: Here we report on selective inactivation of Pseudomonas aeruginosa and Staphylococcus epidermidis, potential pathogens involved in wound infections with pulsed electric fields (PEFs) and antibiotics (mix of penicillin, streptomycin, and nystatin). Results: Using a Taguchi experimental design in vitro, we found that, under similar electric field strengths, the pulse duration is the most important parameter for P. aeruginosa inactivation, followed by the number of pulses and pulse frequency. P. aeruginosa, a potential severe pathogen, is more sensitive than the less pathogenic S. epidermidis to PEF (alone or in combination with antibiotics). Applying 200 pulses with a duration of 60 μs at 2.8 Hz, the minimum electric fields of 308.8 ± 28.3 and 378.4 ± 12.9 V/mm were required to inactive P. aeruginosa and S. epidermidis, respectively. Addition of antibiotics reduced the threshold for minimum electric fields required to inactivate the bacteria. Innovation: This study provides essential information, such as critical electric field parameters for bacteria inactivation, required for developing in vivo treatment and clinical protocols for using PEF for wound healing. Conclusion: A combination of PEFs with antibiotics reduces the electric field threshold required for bacteria disinfection. Such an approach simplifies devices required to disinfect large areas of infected wounds.

Photodynamic Action of Tri-meso (N-methylpyridyl), meso (N-tetradecyl-pyridyl) Porphine on Staphylococcus Epidermidis Biofilms Grown on Ti6Al4V Alloy

Staphylococcus epidermidis is a leading cause of nosocomial infections, and its virulence is attributable to formation of biofilm, especially on implanted devices. Photodynamic treatment (PDT) has been actively investigated for the eradication of bacterial biofilm growing on dental plaques and oral implants. In this study, we used Tri-meso (N-methyl-pyridyl), meso (N-tetradecyl-pyridyl) porphine (C14) for inactivation of two structurally distinct S. epidermidis biofilms grown on Ti6Al4V alloy and compared its photosensitizing efficiency with that of the parent molecule, tetra-substituted N-methylpyridyl-porphine (C1). A more significant reduction in bacterial survival was observed when both bacterial biofilms were exposed to a lower dose of C14, and simultaneously to visible light in comparison with C1. The different responses of both staphylococcal biofilms to C1- or C14-treatment appeared to depend on photosensitizer endocellular concentration. C14 bound to both biofilms to a greater extent than C1. Moreover, C14 penetrates deeper into the bacterial membranes, as determined by fluorescence quenching experiments with methylviologen, allowing for better bacterial killing photoefficiency. Confocal laser scanning microscope (CLSM) analysis indicated damage to bacterial cell membranes in both photodynamically treated biofilms, while disruption of PDT-treated biofilm was confirmed by scanning electron microscopy (SEM). In summary, C14 may be a potential photosensitizer for the inactivation of staphylococcal biofilms for many device-related infections which are accessible to visible light.

Bacterial Communications in Implant Infections: A Target for an Intelligence War

The status of population density is communicated among bacteria by specific secreted molecules, called pheromones or autoinducers, and the control mechanism is called “quorum-sensing”. Quorum-sensing systems regulate the expression of a panel of genes, allowing bacteria to adapt to modified environmental conditions at a high density of population.

The two known different quorum systems are described as the LuxR-LuxI system in gram-negative bacteria, which uses an N-acyl-homoserine lactone (AHL) as signal, and the agr system in gram-positive bacteria, which uses a peptide-tiolactone as signal and the RNAIII as effector molecules. Both in gram-negative and in gram-positive bacteria, quorum-sensing systems regulate the expression of adhesion mechanisms (biofilm and adhesins) and virulence factors (toxins and exoenzymes) depending on population cell density.

In gram-negative Pseudomonas aeruginosa, analogs of signaling molecules such as furanone analogs, are effective in attenuating bacterial virulence and controlling bacterial infections. In gram-positive Staphylococcus aureus, the quorum-sensing RNAIII-inhibiting peptide (RIP), tested in vitro and in animal infection models, has been proved to inhibit virulence and prevent infections. Attenuation of bacterial virulence by quorum-sensing inhibitors, rather than by bactericidal or bacteriostatic drugs, is a highly attractive concept because these antibacterial agents are less likely to induce the development of bacterial resistance.

Staphylococcus Biofilm Components as Targets for Vaccines and Drugs

Staphylococci have become the most common cause of nosocomial infections, especially in patients with predisposing factors such as indwelling or implanted foreign polymer bodies. The pathogenesis of foreign-body associated infections with S. aureus and S. epidermidis is mainly related to the ability of these bacteria to form thick, adherent multilayered biofilms. In a biofilm, staphylococci are protected against antibiotic treatment and attack from the immune system, thus making eradication of the infections problematic. This necessitates the discovery of novel prophylactic and therapeutic strategies to treat these infections. In this review, we provide an overview of staphylococcal biofilm components and discuss new possible approaches to controlling these persistent biofilm-dwelling bacteria.

Prospecting Gene Therapy of Implant Infections

Infection still represents one of the most serious and ravaging complications associated with prosthetic devices. Staphylococci and enterococci, the bacteria most frequently responsible for orthopedic postsurgical and implant-related infections, express clinically relevant antibiotic resistance. The emergence of antibiotic-resistant bacteria and the slow progress in identifying new classes of antimicrobial agents have encouraged research into novel therapeutic strategies. The adoption of antisense or “antigene” molecules able to silence or knock-out bacterial genes responsible for their virulence is one possible innovative approach. Peptide nucleic acids (PNAs) are potential drug candidates for gene therapy in infections, by silencing a basic gene of bacterial growth or by tackling the antibiotic resistance or virulence factors of a pathogen. An efficacious contrast to bacterial genes should be set up in the first stages of infection in order to prevent colonization of periprosthesis tissues. Genes encoding bacterial factors for adhesion and colonization (biofilm and/or adhesins) would be the best candidates for gene therapy. But after initial enthusiasm for direct antisense knock-out or silencing of essential or virulence bacterial genes, difficulties have emerged; consequently, new approaches are now being attempted. One of these, interference with the regulating system of virulence factors, such as agr, appears particularly promising.

Current Methods for Molecular Epidemiology Studies of Implant Infections

Over the last few decades, the number of surgical procedures involving prosthetic materials has greatly multiplied, along with the rising medical and economic impact of implant-associated infections. The need to appropriately counteract and deal with this phenomenon has led to growing efforts to elucidate the etiology, pathogenesis and epidemiology of these types of infections, characterized by opportunistic pathogens. Molecular epidemiology studies have progressively emerged as a leading multitask tool to identify and fingerprint bacterial strains, unveil the complex clonal nature of important pathogens, detect outbreak events, track the origin of the infections, assess the clinical significance of individual strain types, survey their distribution, recognize associations of strain types with specific virulence determinants and/or pathological conditions, assess the role played by the specific components of the virulon, and reveal the phylogeny and the mechanisms through which new strain types have emerged. Despite the many advances that have been made thanks to these flourishing new approaches to molecular epidemiology, a number of critical aspects remain challenging. In this paper, we briefly discuss the current limitations and possible developments of molecular epidemiology methods in the investigation and surveillance of implant infections.

Perspectives on DNA Vaccines. Targeting Staphylococcal Adhesins to Prevent Implant Infections

DNA vaccines consist of a plasmid DNA genetically engineered to produce one or more proteins able to elicit protective immune responses against virulence factors of infectious pathogens. Once introduced into the cells of the host, a DNA vaccine induces a high production of antigens by the endogenous presence of the peptide codifying gene; improves antigen processing and presentation; may be able to simultaneously co-express multiple antigenic molecules; and, lastly, switches on both humoral and cellular immune responses. In this mini-review, we underscore the advantageous characteristics of DNA vaccines compared with traditional ones and provide summaries of some of the more recent studies on them, mainly focusing the possibility of their use in targeting the staphylococcal adhesins that play a key role in the first adhesive phase of implant infections.

INVESTIGATION OF BIOFILM FORMATION IN COAGULASE-NEGATIVE STAPHYLOCOCCI ISOLATED FROM PLATELET CONCENTRATE BAGS

Platelet Concentrates (PCs) are the blood components with the highest rate of bacterial contamination, and coagulase-negative staphylococci (CoNS) are the most frequently isolated contaminants. This study investigated the biofilm formation of 16 contaminated units out of 691 PCs tested by phenotypic and genotypic methods. Adhesion in Borosilicate Tube (ABT) and Congo Red Agar (CRA) tests were used to assess the presence of biofilm. The presence of icaADC genes was assessed by means of the Polymerase Chain Reaction (PCR) technique. With Vitek(r)2, Staphylococcus haemolyticus was considered the most prevalent CoNS (31.25%). The CRA characterized 43.8% as probable biofilm producers, and for the ABT test, 37.5%. The icaADC genes were identified in seven samples by the PCR. The ABT technique showed 85.7% sensitivity and 100% specificity when compared to the reference method (PCR), and presented strong agreement (k = 0.8). This study shows that species identified as PCs contaminants are considered inhabitants of the normal skin flora and they might become important pathogens. The results also lead to the recommendation of ABT use in laboratory routine for detecting biofilm in CoNS contaminants of PCs.

Evidence for inter- and intraspecies biofilm formation variability among a small group of coagulase-negative staphylococci

Coagulase-negative staphylococci (CoNS) are common bacterial colonizers of the human skin. They are often involved in nosocomial infections due to biofilm formation in indwelling medical devices. While biofilm formation has been extensively studied in Staphylococcus epidermidis, little is known regarding other CoNS species. Here, biofilms from six different CoNS species were characterized in terms of biofilm composition and architecture. Interestingly, the ability to form a thick biofilm was not associated with any particular species, and high variability on biofilm accumulation was found within the same species. Cell viability assays also revealed different proportions of live and dead cells within biofilms formed by different species, although this parameter was particularly similar at the intraspecies level. On the other hand, biofilm disruption assays demonstrated important inter- and intraspecies differences regarding extracellular matrix composition. Lastly, confocal laser scanning microscopy experiments confirmed this variability, highlighting important differences and common features of CoNS biofilms. We hypothesized that the biofilm formation heterogeneity observed was rather associated with biofilm matrix composition than with cells themselves. Additionally, our results indicate that polysaccharides, DNA and proteins are fundamental pieces in the process of CoNS biofilm formation.

Proteomics dedicated to biofilmology: What have we learned from a decade of research?

Advances in proteomics techniques over the past decade, closely integrated with genomic and physicochemical approach, have played a great role in developing knowledge of the biofilm lifestyle of bacteria. Despite bacterial proteome versatility, many studies have demonstrated the ability of proteomics approaches to elucidating the biofilm phenotype. Though these investigations have been largely used for biofilm studies in the last decades, they represent, however, a very low percentage of proteomics works performed up to now. Such approaches have offered new targets for combating microbial biofilms by providing a comprehensive quantitative and qualitative overview of their protein cell content. Herein, we summarized the state of the art in knowledge about biofilm physiology after one decade of proteomic analysis. In a second part, we highlighted missing research tracks for the next decade, emphasizing the emergence of posttranslational modifications in proteomic studies stemming from recent advances in mass spectrometry-based proteomics.

Comparative epidemiology of Staphylococcus epidermidis isolates from patients with catheter-related bacteremia and from healthy volunteers

Staphylococcus epidermidis is a major cause of catheter-related bloodstream infections (CRBSIs). Recent studies suggested the existence of well-adapted, highly resistant, hospital-associated S. epidermidis clones. The molecular epidemiology of S. epidermidis in Belgian hospitals and the Belgian community has not been explored yet. We compared a set of 33 S. epidermidis isolates causing CRBSI in hospitalized patients with a set of 33 commensal S. epidermidis isolates. The factors analyzed included resistance to antibiotics and genetic diversity as determined by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and SCCmec typing. Additionally, the presence of virulence-associated mobile genetic elements, the ica operon and the arginine catabolic mobile element (ACME), was assessed and compared against clinical data. CRBSI S. epidermidis isolates were significantly resistant to more antibiotics than commensal S. epidermidis isolates. The two populations studied were very diverse and genetically distinct as only 23% of the 37 PFGE types observed were harbored by both CRBSI and commensal isolates. ACME was found in 76% of S. epidermidis strains, regardless of their origin, while the ica operon was significantly more prevalent in CRBSI isolates than in commensal isolates (P < 0.05). Nine patients presented a clinically severe CRBSI, eight cases of which were due to an ica-positive multiresistant isolate belonging to sequence type 2 (ST2) or ST54. S. epidermidis isolates causing CRBSI were more resistant and more often ica positive than commensal S. epidermidis isolates, which were genetically heterogeneous and susceptible to the majority of antibiotics tested. Clinically severe CRBSIs were due to isolates belonging to two closely related MLST types, ST2 and ST54.

Staphylococcus epidermidis recovered from indwelling catheters exhibit enhanced biofilm dispersal and "self-renewal" through downregulation of agr

Background

In recent years, Staphylococcus epidermidis ( Se) has become a major nosocomial pathogen and the most common cause of infections of implanted prostheses and other indwelling devices. This is due in part to avid biofilm formation by Se on device surfaces. However, it still remains unknown that how the process of Se biofilm development is associated with relapsed infection in such patients.

Results

We have identified clinical Se isolates displaying enhanced biofilm dispersal and self-renewal relative to reference strain. These isolates also exhibit enhanced initial cell attachment, extracellular DNA release, cell autolysis and thicker microcolonies during biofilm development relative to reference strain. Our genetic analyses suggest that these clinical isolates exhibit significant downregulation of RNAIII, the effector molecule of the agr quorum sensing system, and upregulation of the autolysin gene atlE. Isogenic deletion of the agr system in Se 1457 confirmed that agr negatively regulating atlE resulted in enhanced initial cell attachment, extracellular DNA release, cell autolysis and biofilm formation abilities. In contrast, double deletion of agr and atlE significantly abolished these features.

Conclusions

Collectively, these data reveal the role of agr system in long-term biofilm development and pathogenesis during Se caused indwelling devices-related relapsed infection.

Analysis of bacterial biofilms using NMR-based metabolomics

Infectious diseases can be difficult to cure, especially if the pathogen forms a biofilm. After decades of extensive research into the morphology, physiology and genomics of biofilm formation, attention has recently been directed toward the analysis of the cellular metabolome in order to understand the transformation of a planktonic cell to a biofilm. Metabolomics can play an invaluable role in enhancing our understanding of the underlying biological processes related to the structure, formation and antibiotic resistance of biofilms. A systematic view of metabolic pathways or processes responsible for regulating this 'social structure' of microorganisms may provide critical insights into biofilm-related drug resistance and lead to novel treatments. This review will discuss the development of NMR-based metabolomics as a technology to study medically relevant biofilms. Recent advancements from case studies reviewed in this manuscript have shown the potential of metabolomics to shed light on numerous biological problems related to biofilms.

ygs is a novel gene that influences biofilm formation and the general stress response of Staphylococcus epidermidis

Infections caused by the nosocomial pathogen Staphylococcus epidermidis frequently develop on implanted medical devices and involve biofilm formation. Biofilms are surface-attached microbial communities that show increased resistance to drug treatment and mechanisms of innate host defense. In this study, a mutant library of the clinical isolate S. epidermidis 1457 was constructed using mariner-based transposon mutagenesis. About a thousand mutants were screened, and 12 mutants were identified as significantly defective in biofilm formation. We focused on a mutant in which the transposon had inserted in a gene with unknown function, SERP0541, which is annotated as a gene encoding a GSP13-like general stress response protein. The gene was named ygs (encoding an unknown general stress protein). Various stresses, including heat, pH, high osmolarity, and ethanol affected the survival of the ygs mutant to a significantly higher degree than the wild-type strain and led to increased expression of ygs. Furthermore, synthesis of polysaccharide intercellular adhesin (PIA) and transcription of the PIA biosynthetic operon were significantly decreased in the ygs mutant. These results are in accordance with the putative involvement of ygs in stress-response gene regulation and indicate that ygs influences biofilm development by controlling PIA-dependent biofilm accumulation. Moreover, ygs had a significant impact on the formation of biofilms and metastatic disease in two catheter-related rat infection models. Our study shows that the ygs gene controls S. epidermidis biofilm accumulation and stress resistance, representing a key regulator of both structural and physiological biofilm characteristics with a significant impact on biofilm-associated infection.

Current concepts regarding the effect of wound microbial ecology and biofilms on wound healing

Biofilms are a collection of microbes that adhere to surfaces by manufacturing a matrix that shields them from environmental elements. Wound biofilms are difficult to evaluate clinically, and standard culture methods are inadequate for capturing the true bioburden present in the biofilm. New molecular techniques provide the means for rapid detection and evaluation of wound biofilms, and may prove to be useful in the clinical setting. Studies have shown that many commercial topical agents and wound dressings in use are ineffective against the biofilm matrix. At this stage, mechanical debridement appears to be essential in the eradication of a wound biofilm. Topical antimicrobial agents and antibiotics may be effective in the treatment of the wound bed after debridement in the prevention of biofilm reformation.

Role of spx in biofilm formation of Staphylococcus epidermidis

Infections caused by the leading nosocomial pathogen Staphylococcus epidermidis are characterized by biofilm formation on implanted medical devices. In a previous study, we found that ClpP protease plays an essential role in biofilm formation of S. epidermidis. However, the mechanism by which ClpP impacts S. epidermidis biofilms has remained unknown. Here, we show that the Spx protein accumulates in the clpP mutant strain of S. epidermidis and controls biofilm formation of S. epidermidis via a pronounced effect on the transcription of the icaADBC operon coding for the production of the biofilm exopolysaccharide polysaccharide intercellular adhesion (PIA). Notably, in contrast to Staphylococcus aureus, Spx controls PIA expression via an icaR-independent mechanism. Furthermore, Spx affected primary surface attachment, although not by regulating the production of the autolysin AtlE. Our results indicate that ClpP enhances the formation of S. epidermidis biofilms by degrading Spx, a negative regulator of biofilm formation.

New concepts and new weapons in implant infections

Molecular studies have cast light on new facts about the virulence factors of bacteria responsible for implant infections. Recently, the biofilm matrix has been shown to include a variety of important structural components, including DNA, in addition to polysaccharides and proteins. This finding has stimulated interest in substances able to disrupt biofilms by attacking both the poly-N-acetylglucosamine surface polysaccharide (PNAG) and the extracellular DNA (eDNA), namely, dispersin B, a PNAG-degrading enzyme, and DNase I. The therapeutic potential of these enzymes are reviewed in this issue of IJAO, as well as the ability of the excretions/secretions of the medicinal maggot Lucilia sericata to disrupt Staphylococcus epidermidis biofilms. The activity of bacterial proteases causes the release of eDNA, critical for the early development of biofilms. This complex process, including suicidal and fratricidal mechanisms, is also presented in the current issue of IJAO. The different sensitivities of S. aureus and S. epidermidis to enzymatic anti-biofilm agents and to the host's first line of defense, as well as the importance of knowing the cascade of regulatory genes in bacteria so as to interfere with biofilm production using gene therapy or quorum sensing inhibitors are also discussed in this issue. Other innovative approaches consist in disrupting biofilms by exposing them to photodynamic substances and simultaneously to visible light, and in coating biomaterial surfaces with organic molecules to prevent protein adsorption and biofilm formation.

Epidemiology and characterization ofStaphylococcus epidermidisisolates from humans, raw bovine milk and a dairy plant

Geographically relatedStaphylococcus epidermidisisolates from human patients (n=30), dairy farms (farmers and individual raw milk from cattle,n=36) and a dairy plant (n=55) were examined for epidemiological relatedness by pulsed-field gel electrophoresis and, usingin vitromethods, for the ability to produce biofilm and antimicrobial resistance. Methicillin-resistant isolates (MRSE) were also identified and characterized. Isolates from farmers and dairy cattle were found to be genetically related, while isolates from human patients were highly diverse. Some dairy plant isolates (18·2%) were closely related to those from dairy farms. Biofilm production and resistance to antimicrobial agents were most typical for isolates from human patients, of which 76·7% were MRSE. Methicillin resistance was also widespread in farm-related isolates (61·1%). This study indicates the possible transmission ofS. epidermidisbetween cattle and farmers. Dairy products were not proven to be an important source of either human infections or methicillin-resistant strains.

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.

Photodynamic action of merocyanine 540 on Staphylococcus epidermidis biofilms

Photodynamic treatment (PDT) has been proposed as a new approach for inactivation of biofilms associated with medical devices that are resistant to chemical additives or biocides. In this study, we evaluated the antimicrobial activity of merocyanine 540 (MC 540), a photosensitizing dye that is used for purging malignant cells from autologous bone marrow grafts, against Staphylococcus epidermidis biofilms. Effect of the combined photodynamic action of MC 540 and 532 nm laser was investigated on the viability and structure of biofilms of two Staphylococcus epidermidis strains, RP62A and 1457. Significant inactivation of cells was observed when biofilms were exposed to MC 540 and laser simultaneously. The effect was found to be light dose-dependent but S. epidermidis 1457 biofilm proved to be slightly more susceptible than S. epidermidis RP62A biofilm. Furthermore, significant killing of both types of cells was attained even when a fixed light dose was delivered to the biofilms. Confocal laser scanning microscope (CLSM) analysis indicated damage to bacterial cell membranes in photodynamically treated biofilms, while disruption of PDT-treated biofilm was confirmed by scanning electron microscopy (SEM).

Foreign body infections due to Staphylococcus epidermidis

Staphylococcal infections are one of the main causes of complications in patients with implanted foreign prosthetic material. Implants are associated with a significant reduction of the threshold at which contaminating Gram-positive bacteria, particularly Staphylococcus epidermidis, become infectious and develop a biofilm with phenotypic resistance to almost all antibiotics. A 1000-fold increase in minimal bactericidal levels against most antibiotics except rifampin has been repeatedly observed. Since only removal of the foreign material reverses these phenomena, the clinical challenge consists in finding approaches to cure the infection without removal of the implanted device. Rifampin combinations with other antibiotics, administration of exceedingly high antibiotic concentrations in situ, and early therapy before biofilm development are efficacious. Although these strategies have dramatically improved the outcome of foreign body infections, an improved understanding of biofilm-grown S. epidermidis is necessary to develop new antibacterial agents. Here, we review the pathogenesis, prevention, and treatment of implant infections due to S. epidermidis and highlight some new compounds with already promising in vitro results.

Resistance profiles in surgical-site infection

Surgical-site infections (SSIs) remain a common complication, affecting some 5% of patients undergoing surgical procedures and can sometimes present a major challenge after surgery with life-threatening septic illness. The appearance of organisms that are often resistant to common antibiotic treatment is of great concern. Staphylococcus aureus is the organism most commonly recovered from infected surgical wounds, and usually contaminates wounds from the patients own skin. SSIs occur despite appropriate skin disinfection, sterilization of instruments, use of gown and gloves, appropriate sterile technique and prophylactic antimicrobials. In fact, it is difficult to maintain a sterile field over time, and most wounds become contaminated throughout the course of surgery. Methicillin-resistant S. aureus (MRSA) first arose in the hospital setting, but have more recently evolved in the community. Such community-acquired MRSA are genetically different and seem to be even more virulent owing to genes that encode virulence factors, such as staphylococcal cassette chromosome mec type IV and Panton-Valentine leukocidin. The purpose of this review is to summarize characteristics of frequently isolated bacterial strains from SSIs. The focus will be on Gram-positive organisms because of their increasing prevalence in SSIs and their high potential to develop resistance against several antibiotic agents, including vancomycin.

Biofilm-forming associated genotypic and phenotypic characteristics of Staphylococcus spp. isolated from animals and air

Biological monitoring is performed to detect and analyze microorganisms that have continuously made an effort to survive in the environment. Of such microorganisms, Staphylococcus spp. is considered a common cause of nosocomial and environmental infections., Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs) are required for the adhesion and biofilm formation of Staphylococci. Thirty-six and thirty-five Staphylococci isolated from animals and air, respectively, were analyzed. Biofilm formation and ten MSCRAMM genes were investigated using Congo red agar, tissue culture plate methods, and PCR. Airborne isolates were shown to have higher adherence and stronger biofilm formation than those from animals. The prevalence of MSCRAMM genes from air isolates was also higher than those from animals. Of the genes, eno was mainly associated with biofilm formation in both animals and airborne isolates (P<0.05). Moreover, the rate of airborne isolates harboring the eno gene was higher than in animal isolates. These results indicated that analysis of MSCRAMM genes with a phenotypic assay might be a helpful bacterial control system for the environment.

Prevalence of genes encoding for staphylococcal leukocidal toxins among clinical isolates of Staphylococcus aureus from implant orthopedic infections

Staphylococcus aureus has emerged as a major cause of implant infections. It is known that it is able to produce several toxins that contribute to its armory of virulent weapons, but there are still no data on their prevalence among isolates recovered from biomaterial-centered infections. In this study, 200 Staphylococcus aureus isolates from infections related to different types of orthopedic implants (hip and knee arthroprostheses, internal and external fixation devices) were tested by polymerase chain reaction for the prevalence of genes encoding for leukotoxins. Although almost all isolates were positive for the ã-hemolysin gene (99%), none was positive for lukM. The leukotoxin genes lukE/lukD were found in 67% of isolates. The presence of lukE/lukD was significantly associated with that of Accessory Gene Regulatory locus agr II. The lukE/lukD-positive isolates were significantly more prevalent in the staphylococcal isolates from knee arthroprostheses than in the isolates from the other implant types. The genes encoding Panton-Valentine leukocidin components were detected in only one isolate that, curiously enough, was taken solely from a knee arthroprosthesis infection.

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.

Yersinia pestis biofilm in the flea vector and its role in the transmission of plague

Transmission by fleabite is a relatively recent evolutionary adaptation of Yersinia pestis, the bacterial agent of bubonic plague. To produce a transmissible infection, Y. pestis grows as an attached biofilm in the foregut of the flea vector. Biofilm formation both in the flea foregut and in vitro is dependent on an extracellular matrix (ECM) synthesized by the Yersinia hms gene products. The hms genes are similar to the pga and ica genes of Escherichia coli and Staphylococcus epidermidis, respectively, that act to synthesize a poly-beta-1,6-N-acetyl-d-glucosamine ECM required for biofilm formation. As with extracellular polysaccharide production in many other bacteria, synthesis of the Hms-dependent ECM is controlled by intracellular levels of cyclic-di-GMP. Yersinia pseudotuberculosis, the food- and water-borne enteric pathogen from which Y. pestis evolved recently, possesses identical hms genes and can form biofilm in vitro but not in the flea. The genetic changes in Y. pestis that resulted in adapting biofilm-forming capability to the flea gut environment, a critical step in the evolution of vector-borne transmission, have yet to be identified. During a flea bite, Y. pestis is regurgitated into the dermis in a unique biofilm phenotype, and this has implications for the initial interaction with the mammalian innate immune response.

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.

Potential use of poly-N-acetyl-beta-(1,6)-glucosamine as an antigen for diagnosis of staphylococcal orthopedic-prosthesis-related infections

Staphylococcus aureus and coagulase-negative staphylococci are microorganisms most frequently isolated from orthopedic-implant-associated infections. Their capacity to maintain these infections is thought to be related to their ability to form adherent biofilms. Poly-N-acetyl-beta-(1,6)-glucosamine (PNAG) is an important constituent of the extracellular biofilm matrix of staphylococci. In the present study, we explored the possibility of using PNAG as an antigen for detecting antibodies in the blood sera of patients with staphylococcal orthopedic-prosthesis-associated infections. First, we tested the presence of anti-PNAG antibodies in an animal model, in the blood sera of guinea pigs that developed an implant-associated infection caused by biofilm-forming, PNAG-producing strains of Staphylococcus epidermidis. Animals infected with S. epidermidis RP62A showed levels of anti-PNAG immunoglobulin G (IgG) significantly higher than those of the control group. The comparative study of healthy individuals and patients with staphylococcal prosthesis-related infections showed that (i) relatively high levels of anti-PNAG IgG were present in the blood sera of the healthy control group, (ii) the corresponding levels in the infected patients were slightly but not significantly higher, and (iii) only 1 of 10 patients had a level of anti-PNAG IgM significantly higher than that of the control group. In conclusion, the encouraging results obtained in the animal study could not be readily applied for the diagnosis of staphylococcal orthopedic-prosthesis-related infections in humans, and PNAG does not seem to be an appropriate antigen for this purpose. Further studies are necessary to determine whether the developed enzyme-linked immunosorbent assay method could serve as a complementary test in the individual follow-up treatment of such infections caused by PNAG-producing staphylococci.

Role of ClpP in biofilm formation and virulence of Staphylococcus epidermidis

Infections caused by the leading nosocomial pathogen Staphylococcus epidermidis are characterized by biofilm formation on implanted medical devices. However, the molecular basis of biofilm formation and its regulation are not completely understood. Here, we describe an important role of the ClpP protease in biofilm development and virulence of S. epidermidis. We constructed an isogenic clpP mutant strain of a biofilm-forming clinical isolate of S. epidermidis. The mutant strain showed decreased biofilm formation in vitro and reduced virulence in a rat model of biofilm-associated infection. Biofilm forming ability of the mutant strain could be restored by expressing clpP on a plasmid, but not when a catalytically inactive allele of clpP gene was introduced. These observations indicate that the peptidase function of ClpP determines its role in biofilm formation. Experimental data in this work also suggested that clpP influenced initial attachment of bacteria on the plastic surface, the first step of biofilm formation. Furthermore, clpP was found to be regulated by the quorum-sensing agr, suggesting that part of the previously described influence of agr on the initial attachment to plastic surfaces may be mediated by clpP.

Staphylococcus epidermidis forms biofilms under simulated platelet storage conditions

BACKGROUND

Staphylococcus epidermidis grows slowly in platelet (PLT) preparations compared to other bacteria, presenting the possibility of missed detection by routine screening. S. epidermidis is a leading cause of nosocomial sepsis, with virulence residing in its ability to establish chronic infections through production of slime layers, or biofilms, on biomedical devices. This study aims to establish biofilm formation (BF) as a mode of growth by S. epidermidis in PLT preparations.

STUDY DESIGN AND METHODS

Biofilm-positive (BFpos) and -negative (BFneg) S. epidermidis strains were grown in whole blood-derived PLTs (WBDPs) and in glucose-rich medium (TSBg). An assay for BF was adapted for cultures grown in WBDPs or filtered WBDPs in polystyrene culture plates. Bacterial attachment to polyvinylchloride PLT bags and PLTs was examined by scanning electron microscopy.

RESULTS

Both strains display similar growth profiles in WBDPs and TSBg. Unexpectedly, evidence of BF was observed on PLT bags and on PLTs directly, not only by the BFpos strain but also by the BFneg strain. The BFpos strain displayed greater plastic adherence than the BFneg strain in WBDPs (p < 0.05). BF by the BFneg strain was approximately 10-fold greater in WBDPs compared to TSBg (p < 0.05), likely by use of PLTs as a scaffold. Furthermore, BF by S. epidermidis was significantly decreased when PLT concentration was reduced 1000-fold.

CONCLUSIONS

S. epidermidis forms biofilms on PLT aggregates and on PLT bags under PLT storage conditions. Our results demonstrate that the PLT storage environment can promote a BF growth mechanism for contaminant bacteria.

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.

Emerging Staphylococcus species as new pathogens in implant infections

The vast use of prosthetic materials in medicine over the last decades has been accompanied by the appearance of new opportunistic pathogens previously considered incapable of causing infections with significant morbidity and/or mortality. In this regard, the genus Staphylococcus enlisting numerous species usually characterized by a saprophytic habit covers a special role. Apart from Staphylococcus aureus and Staphylococcus epidermidis, well known for their large prevalence in implant-related infections, a number of further staphylococcal species are progressively being indicated for their pathogenic potential. The increasing attention on these opportunistic bacteria is due to an ever growing number of clinical reports, which is also deriving from a more accurate identification of these species with currently available techniques. This synopsis intends to offer an overview on recently emerging coagulase-negative staphylococci (CoNS) as well as coagulase-positive/-variable staphylococci exhibiting distinct traits of virulence, pathogenicity, and epidemiologic impact depending among others on the medical field, the type of prosthetic device and its anatomic location.

Depression of biofilm formation and antibiotic resistance by sarA disruption in Staphylococcus epidermidis

AIM: To study the effects of disruption of sarA gene on biofilm formation and antibiotic resistance of Staphylococcus epidermidis (S. epidermidis).

METHODS: In order to disrupt sarA gene, the double-crossover homologous recombination was applied in S. epidermidis RP62A, and tetracycline resistance gene (tet) was used as the selective marker which was amplified by PCR from the pBR322 and inserted into the locus between sarA upstream and downstream, resulting in pBT2△sarA. By electroporation, the plasmid pBT2△sarA was transformed into S. epidermidis. Gene transcription was detected by real-time reverse transcription-PCR (RT-PCR). Determination of biofilm was performed in 96-well flat-bottomed culture plates, and antibiotic resistance was analyzed with test tube culture by spectrophotometry at 570 nm respectively.

RESULTS: A sarA disrupted strain named S. epidermidis RP62A△sarA was constructed, which was completely defective in biofilm formation, while the sarA complement strain RP62A△sarA (pHPS9sarA) restored the biofilm formation phenotype. Additionally, the knockout of sarA resulted in decreased erythromycin and kanamycin resistance of S. epidermidis RP62A. Compared to the original strain, S. epidermidis RP62A△sarA had an increase of the sensitivity to erythromycin at 200-400 μg/mL and kanamycin at 200-800 μg/mL respectively.

CONCLUSION: The knockout of sarA can result in the defect in biofilm formation and the decreased erythromycin and kanamycin resistance in S. epidermidis RP62A.