Biofilm formation in medical device-related infection

Antibacterial surfaces by adsorptive binding of polyvinyl-sulphonate-stabilized silver nanoparticles

This paper presents a novel and facile method for the generation of efficient antibacterial coatings which can be applied to practically any type of substrate. Silver nanoparticles were stabilized with an adsorbed surface layer of polyvinyl sulphonate (PVS). This steric layer provided excellent colloidal stability, preventing aggregation over periods of months. PVS-coated silver nanoparticles were bound onto amine-containing surfaces, here produced by deposition of an allylamine plasma polymer thin film onto various substrates. SEM imaging showed no aggregation upon surface binding of the nanoparticles; they were well dispersed on amine surfaces. Such nanoparticle-coated surfaces were found to be effective in preventing attachment of Staphylococcus epidermidis bacteria and also in preventing biofilm formation. Combined with the ability of plasma polymerization to apply the thin polymeric binding layer onto a wide range of materials, this method appears promising for the fabrication of a wide range of infection-resistant biomedical devices.

Microscopic detection of viable Staphylococcus epidermidis in peri-implant tissue in experimental biomaterial-associated infection, identified by bromodeoxyuridine incorporation

Infection of biomedical devices is characterized by biofilm formation and colonization of surrounding tissue by the causative pathogens. To investigate whether bacteria detected microscopically in tissue surrounding infected devices were viable, we used bromodeoxyuridine (BrdU), a nucleotide analogue that is incorporated into bacterial DNA and can be detected with antibodies. Infected human tissue was obtained postmortem from patients with intravascular devices, and mouse biopsy specimens were obtained from mice with experimental biomaterial infection. In vitro experiments showed that Staphylococcus epidermidis incorporated BrdU, as judged from staining of the bacteria with anti-BrdU antibodies. After incubation of bacteria with BrdU and subsequent staining of microscopic sections with anti-BrdU antibodies, bacteria could be clearly visualized in the tissue surrounding intravascular devices of deceased patients. With this staining technique, relapse of infection could be visualized in mice challenged with a low dose of S. epidermidis and treated with dexamethasone between 14 and 21 days after challenge to suppress immunity. This confirms and extends our previous findings that pericatheter tissue is a reservoir for bacteria in biomaterial-associated infection. The pathogenesis of the infection and temporo-spatial distribution of viable, dividing bacteria can now be studied at the microscopic level by immunolabeling with BrdU and BrdU antibodies.

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

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

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

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

Influences of protein films on antibacterial or bacteria-repellent surface coatings in a model system using silicon wafers

Immobilization of defined chemical functionalities to biomaterial surfaces is employed to optimize them not only for tissue compatibility but also for prevention of bacterial infection. Grafting surfaces with chains of poly(ethylene glycol) (PEG) results in bacterial repellence whereas modification with cationic groups conveys them with bactericidal properties. Since biomaterials in situ will become exposed to a protein-rich environment, it is necessary to investigate the influence of prior protein adsorption on the antibacterial activity of this type of chemical surface modification. In the present study, we immobilized short-chain PEG and two pyridinium group-containing methacrylate monomers, 12-methacryloyloxydodecylpyridinium bromide (MDPB) and 6-methacryloyloxyhexylpyridinium chloride (MHPC), to silicon wafer model surfaces to investigate the influence of prior protein adsorption on the bactericidal activity of the surface coating towards subsequently attached bacteria. Adsorbed amounts of human serum albumin and salivary proteins were found to be two times higher on cationic compared to PEG-modified surfaces. An analogous tendency was found for attachment of Streptococcus gordonii and Streptococcus mutans to the same surfaces without prior protein exposure. However, most bacteria attached to cationic surfaces were found to be dead. Prior exposure of cationic surfaces to protein solutions drastically altered bacterial attachment dependent on the type of protein solution and bacterial species employed. Significantly, the original bactericidal activity of pyridinium-coated surfaces was found greatly reduced upon adsorption of a protein film. As a conclusion we propose that future approaches should combine the protein- and bacteria-repellent properties of PEG-coatings with the bactericidal function of charged cationic groups.

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).

Biofilm formation by Staphylococcus haemolyticus

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

Adhesion forces between Staphylococcus epidermidis and surfaces bearing self-assembled monolayers in the presence of model proteins

Self-assembled monolayers (SAMs) are being developed into coatings to reduce microbial biofilm formation on biomaterials. To test anti-adhesion properties, SAMs can be easily constructed on gold, and used to represent a coated biomaterial. However, coatings that prevent bacterial adhesion must also resist protein adsorption. We explored the competitive effects of bacteria and protein for adsorption to SAMs, choosing fetal bovine serum (FBS) to represent protein non-specific binding, and fibronectin (FN) to evaluate ligand/receptor binding. Staphylococcus epidermidis were immobilized on an atomic force microscope (AFM) tip and used as a force probe to detect the interaction forces between bacteria and gold-coated SAMs. The SAMs tested were alkanethiol molecules terminating in isophthalic acid (IPA) or isophthalic acid with silver (IAG). While S. epidermidis showed weak interactions with FBS, the bacteria showed strong adhesion with FN, due to ligand/receptor binding. Bacterial retention and viability experiments were correlated with the force measurements. S. epidermidis interacting with IAG SAMs showed a loss of viability, due to the mobility of silver ions. For most substrata, there was a link between high adhesion forces with bacteria and a high percentage of dead cells being retained on that substratum (even in the absence of a specific biocidal effect, such as silver). This may suggest that high adhesion forces can cause stress to the bacteria which contributed to their death. The relationship between highly adhesive SAMs and bacterial inactivation may be useful in future biomaterial design. When evaluating coatings for biomaterials, it is important to consider the interplay between bacteria, proteins, and the coating material.

Development of real-time in vivo imaging of device-related Staphylococcus epidermidis infection in mice and influence of animal immune status on susceptibility to infection

Staphylococcus epidermidis is the leading cause of hospital-acquired device-related infections, but there is a lack of suitable methods to investigate the pathogenesis of S. epidermidis infection. We created a bioluminescent strain of S. epidermidis and developed a subcutaneous catheter-related murine infection model for real-time monitoring of biofilm-associated infection. Additionally, we compared severely immunocompromised and immunocompetent mice, demonstrating the substantial effect of animal immune status on susceptibility to experimentally induced S. epidermidis disease. This study presents a novel approach for investigating the in vivo details of the pathogenesis of S. epidermidis infection.

Biofilm formation induces C3a release and protects Staphylococcus epidermidis from IgG and complement deposition and from neutrophil-dependent killing

BACKGROUND

Biofilm formation is considered to be an important virulence factor of the opportunistic pathogen Staphylococcus epidermidis. We hypothesized that biofilm formation could interfere with the deposition of immunoglobulins and complement on the bacterial surface, leading to diminished activation of the complement system and protection from killing by human phagocytes.

METHODS

The killing of biofilm-encased and planktonically grown wild-type (wt) S. epidermidis and the killing of an isogenic biofilm-negative ica mutant (ica(-)) by human polymorphonuclear neutrophils (PMNs) were compared. C3a induction and deposition of C3b and immunoglobulin G (IgG) on the bacteria after opsonization with human serum were assessed by enzyme-linked immunosorbent assay, flow cytometry, and electron microscopy. The virulence of the bacterial strains was compared in a mouse model of catheter-associated infection.

RESULTS

Biofilm-embedded wt S. epidermidis was killed less well by human PMNs and induced more C3a than planktonically grown wt and ica(-) S. epidermidis. However, the deposition of C3b and IgG on the bacterial surface was diminished in biofilm-encased staphylococci. wt S. epidermidis was more virulent in implant-associated infections and was killed more slowly than ica(-) in ex vivo assays of killing by PMNs.

CONCLUSIONS

The results indicate that prevention of C3b and IgG deposition on the bacterial surface contributes to the biofilm-mediated protection of S. epidermidis from killing by PMNs.

Substrata mechanical stiffness can regulate adhesion of viable bacteria

The competing mechanisms that regulate adhesion of bacteria to surfaces and subsequent biofilm formation remain unclear, though nearly all studies have focused on the role of physical and chemical properties of the material surface. Given the large monetary and health costs of medical-device colonization and hospital-acquired infections due to bacteria, there is considerable interest in better understanding of material properties that can limit bacterial adhesion and viability. Here we employ weak polyelectrolyte multilayer (PEM) thin films comprised of poly(allylamine) hydrochloride (PAH) and poly(acrylic acid) (PAA), assembled over a range of conditions, to explore the physicochemical and mechanical characteristics of material surfaces controlling adhesion of Staphylococcus epidermidis bacteria and subsequent colony growth. Although it is increasingly appreciated that eukaryotic cells possess subcellular structures and biomolecular pathways to sense and respond to local chemomechanical environments, much less is known about mechanoselective adhesion of prokaryotes such as these bacteria. We find that adhesion of viable S. epidermidis correlates positively with the stiffness of these polymeric substrata, independently of the roughness, interaction energy, and charge density of these materials. Quantitatively similar trends observed for wild-type and actin analogue mutant Escherichia coli suggest that these results are not confined to only specific bacterial strains, shapes, or cell envelope types. These results indicate the plausibility of mechanoselective adhesion mechanisms in prokaryotes and suggest that mechanical stiffness of substrata materials represents an additional parameter that can regulate adhesion of and subsequent colonization by viable bacteria.

Microbe repelling coated stainless steel analysed by field emission scanning electron microscopy and physicochemical methods

Coating of stainless steel with diamond-like carbon or certain fluoropolymers reduced or almost eliminated adhesion and biofilm growth of Staphylococcus epidermidis, Deinococcus geothermalis, Meiothermus silvanus and Pseudoxanthomonas taiwanensis. These species are known to be pertinent biofilm formers on medical implants or in the wet-end of paper machines. Field emission scanning electron microscopic analysis showed that Staph. epidermidis, D. geothermalis and M. silvanus grew on stainless steel using thread-like organelles for adhesion and biofilm formation. The adhesion threads were fewer in number on fluoropolymer-coated steel than on plain steel and absent when the same strains were grown in liquid culture. Psx. taiwanensis adhered to the same surfaces by a mechanism involving cell ghosts on which the biofilm of live cells grew. Hydrophilic (diamond-like carbon) or hydrophobic (fluoropolymer) coatings reduced the adherence of the four test bacteria on different steels. Selected topographic parameters, including root-mean-square roughness (S (q)), skewness (S (sk)) and surface kurtosis (S (ku)), were analysed by atomic force microscopy. The surfaces that best repelled microbial adhesion of the tested bacteria had higher skewness values than those only slightly repelling. Water contact angle, measured (theta (m)) or roughness corrected (theta (y)), affected the tendency for biofilm growth in a different manner for the four test bacteria.

Activity of daptomycin on biofilms produced on a plastic support by Staphylococcus spp

The aim of this study was to assess whether the novel lipopeptide daptomycin might be capable of disrupting or inhibiting the synthesis of biofilms produced by staphylococci. Fourteen recently isolated slime-producing methicillin-susceptible (MET-S) and methicillin-resistant (MET-R) strains (three MET-S Staphylococcus aureus, three MET-R S. aureus, three MET-S Staphylococcus epidermidis, three MET-R S. epidermidis and two vancomycin-intermediate S. aureus (VISA)) were tested. Slime formation on polystyrene plates was quantified spectrophotometrically. Daptomycin (2-64 mg/L) inhibited slime synthesis by > or =80% in MET-S strains, by 60-80% in MET-R S. aureus and by 70-95% in MET-R S. epidermidis. At 64 mg/L, biofilm synthesis decreased by 80% in the VISA isolates. Daptomycin also disrupted pre-formed biofilm: >50% breakdown of initial biofilm (5h) was observed in all strains. Disruption of mature biofilms (48 h), in terms of percentage, was more variable depending on the strain, ranging from ca. 20% in a MET-R S. epidermidis strain to almost 70% in two MET-S strains (one S. aureus and one S. epidermidis). Daptomycin at concentrations achievable during therapy promoted a statistically significant inhibition of slime synthesis (preventing biofilm building) and induced slime disruption (disaggregating its structure) both in initial and mature biofilms on a plastic support in all staphylococcal strains studied.

Antibiotic multiresistance strictly associated with IS256 andica genes inStaphylococcus epidermidis strains from implant orthopedic infections

In this study the presence both of the ica genes, encoding for biofilm exopolysaccharide production, and the insertion sequence IS256, a mobile element frequently associated to transposons, was investigated in relationship with the prevalence of antibiotic resistance among Staphylococcus epidermidis strains. The investigation was conducted on 70 clinical isolates derived from orthopedic implant infections. Among the clinical isolates investigated a dramatic high level of association was found between the presence of ica genes as well as of IS256 and multiple-resistance to all the antibiotics tested (oxacillin, penicillin, gentamicin, erythromycin, clindamycin, chloramphenicol, sulfamethoxazole + trimethoprim, ciprofloxacin, vancomycin). Noteworthy, a striking full association between the presence of IS256 and resistance to gentamicin was found, being none of the IS256-negative strain resistant to this antibiotic. This association is probably because of the link of the corresponding aminoglycoside-resistance genes, and IS256, often co-existing within the same staphylococcal transposon. In conclusion, in orthopedics, the presence of ica genes and that of IS256 in S. epidermidis genome should both be considered as informative markers of clinically relevant strains equipped with greatest and broadest resistance potential to survive to medical treatments.

Biofilm formation of the pathogens of fatal bacterial granuloma after trauma: potential mechanism underlying the failure of traditional antibiotic treatments

The pathogen of a new type of disease - fatal bacterial granuloma after trauma (FBGT) - was found to be Propionibacterium acnes (P. acnes). Although in vitro studies showed that the pathogenic P. acnes are sensitive to conventional antibiotics, treatments of FBGT patients with these antibiotics were ineffective. The underlying mechanisms were not clear. Since P. acnes are able to form biofilm on orthopaedic biomaterials in vitro, and pathogenic P. acnes of acnes vulgaris was known to form biofilm in vivo, we hypothesize that the pathogens of FBGT are also able to form biofilm during the pathogenesis, which may be 1 of the reasons for antibiotics tolerance of FBGT. Biofilm forming capacity of the pathogens of FBGT were examined with XTT reduction method, as well as with scanning electron microscope. The effect of long-term subminimal inhibitory concentration (MIC) lincomycin on the biofilm forming ability of the pathogens was also tested. Our results show that both the type strain (NCTC737) and the pathogenic P. acnes of FBGT can form biofilm in vitro. These data demonstrated the biofilm formation of the FBGT pathogens in vitro, and its acceleration by lincomycin, which may be 1 of the major mechanisms for the failure of antibiotic treatment.

Pharmacokinetic and Pharmacodynamic Aspects of Antibiotic Use in High-Risk Populations

The study of pharmacokinetics includes the absorption, distribution, metabolism, and elimination of drugs. The pharmacologic effect that a medication has on the body is known as pharmacodynamics. With antimicrobials, pharmacokinetic and pharmacodynamic parameters become especially important because of the association between host drug concentrations, microorganism eradication, and resistance. This article focuses on the pharmacokinetic changes that can occur with antimicrobials when they are used in patients at high risk of infections and how they influence pharmacodynamic effects. The populations described here include patients with obesity and diabetes mellitus, renal or hepatic failure, chronic lung disease, severe burns, and long-term prosthetic devices and the elderly.

Staphylococcal biofilm exopolysaccharide protects against Caenorhabditis elegans immune defenses

Staphylococcus epidermidis and Staphylococcus aureus are leading causes of hospital-acquired infections that have become increasingly difficult to treat due to the prevalence of antibiotic resistance in these organisms. The ability of staphylococci to produce biofilm is an important virulence mechanism that allows bacteria both to adhere to living and artificial surfaces and to resist host immune factors and antibiotics. Here, we show that the icaADBC locus, which synthesizes the biofilm-associated polysaccharide intercellular adhesin (PIA) in staphylococci, is required for the formation of a lethal S. epidermidis infection in the intestine of the model nematode Caenorhabditis elegans. Susceptibility to S. epidermidis infection is influenced by mutation of the C. elegans PMK-1 p38 mitogen-activated protein (MAP) kinase or DAF-2 insulin-signaling pathways. Loss of PIA production abrogates nematocidal activity and leads to reduced bacterial accumulation in the C. elegans intestine, while overexpression of the icaADBC locus in S. aureus augments virulence towards nematodes. PIA-producing S. epidermidis has a significant survival advantage over ica-deficient S. epidermidis within the intestinal tract of wild-type C. elegans, but not in immunocompromised nematodes harboring a loss-of-function mutation in the p38 MAP kinase pathway gene sek-1. Moreover, sek-1 and pmk-1 mutants are equally sensitive to wild-type and icaADBC-deficient S. epidermidis. These results suggest that biofilm exopolysaccharide enhances virulence by playing an immunoprotective role during colonization of the C. elegans intestine. These studies demonstrate that C. elegans can serve as a simple animal model for studying host–pathogen interactions involving staphylococcal biofilm exopolysaccharide and suggest that the protective activity of biofilm matrix represents an ancient conserved function for resisting predation.

Biofilm is an agglomeration of microbes bound together by a slimy matrix composed of excreted proteins and polysaccharide polymers. Most bacteria in the environment reside in biofilms, as do 80% or more of those causing human infections, according to some estimates. During infection, biofilm matrix acts as a safe haven, protecting bacterial cells from antibiotics, immune cells, and antimicrobial factors. In this report, we demonstrate that the ability of Staphylococcus epidermidis to produce a lethal infection within the intestinal tract of the roundworm Caenorhabditis elegans depends on the S. epidermidis intercellular adhesion (ica) locus, which is responsible for the synthesis of the principal exopolysaccharide of staphylococcal biofilm, polysaccharide intercellular adhesin (PIA). Using a collection of bacterial and nematode mutants, we show that PIA promotes infection by working against protective immune factors controlled by the C. elegans SEK-1 PMK-1 p38 mitogen-activated protein kinase pathway. In addition to providing further evidence for the immunoprotective function of the biofilm polymer PIA, these results show that C. elegans can be used in a simple, live animal model for the study of host–pathogen interactions involving biofilm matrix.

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

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

Polysaccharide intercellular adhesin or protein factors in biofilm accumulation of Staphylococcus epidermidis and Staphylococcus aureus isolated from prosthetic hip and knee joint infections

Nosocomial staphylococcal foreign-body infections related to biofilm formation are a serious threat, demanding new therapeutic and preventive strategies. As the use of biofilm-associated factors as vaccines is critically restricted by their prevalence in natural staphylococcal populations we studied the distribution of genes involved in biofilm formation, the biofilm phenotype and production of polysaccharide intercellular adhesin (PIA) in clonally independent Staphylococcus aureus and Staphylococcus epidermidis strains isolated from prosthetic joint infections after total hip or total knee arthroplasty. Biofilm formation was detected in all S. aureus and 69.2% of S. epidermidis strains. Importantly, 27% of biofilm-positive S. epidermidis produced PIA-independent biofilms, in part mediated by the accumulation associated protein (Aap). Protein-dependent biofilms were exclusively found in S. epidermidis strains from total hip arthroplasty (THA). In S. aureus PIA and proteins act cooperatively in biofilm formation regardless of the infection site. PIA and protein factors like Aap are of differential importance for the pathogenesis of S. epidermidis in prosthetic joint infections (PJI) after THA and total knee arthroplasty (TKA), implicating that icaADBC cannot serve as a general virulence marker in this species. In S. aureus biofilm formation proteins are of overall importance and future work should focus on the identification of functionally active molecules.

Microbial interactions in Staphylococcus epidermidis biofilms

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