Characterization of Staphylococcus epidermidis polysaccharide intercellular adhesin/hemagglutinin in the pathogenesis of intravascular catheter-associated infection in a rat model

Etiology, pathology, and host-impaired immunity in medical implant-associated infections

Host impaired immunity and pathogens adhesion factors are the key elements in analyzing medical implant-associated infections (MIAI). The infection chances are further influenced by surface properties of implants. This review addresses the medical implant-associated pathogens and summarizes the etiology, pathology, and host-impaired immunity in MIAI. Several bacterial and fungal pathogens have been isolated from MIAI; together, they form cross-kingdom species biofilms and support each other in different ways. The adhesion factors initiate the pathogen's adherence on the implant's surface; however, implant-induced impaired immunity promotes the pathogen's colonization and biofilm formation. Depending on the implant's surface properties, immune cell functions get slow or get exaggerated and cause immunity-induced secondary complications resulting in resistant depression and immuno-incompetent fibro-inflammatory zone that compromise implant's performance. Such consequences lead to the unavoidable and straightforward conclusion for the downstream transformation of new ideas, such as the development of multifunctional implant coatings.

Increased local bone turnover in patients with chronic periprosthetic joint infection

Aims

The management of periprosthetic joint infection (PJI) remains a major challenge in orthopaedic surgery. In this study, we aimed to characterize the local bone microstructure and metabolism in a clinical cohort of patients with chronic PJI.

Methods

Periprosthetic femoral trabecular bone specimens were obtained from patients suffering from chronic PJI of the hip and knee (n = 20). Microbiological analysis was performed on preoperative joint aspirates and tissue specimens obtained during revision surgery. Microstructural and cellular bone parameters were analyzed in bone specimens by histomorphometry on undecalcified sections complemented by tartrate-resistant acid phosphatase immunohistochemistry. Data were compared with control specimens obtained during primary arthroplasty (n = 20) and aseptic revision (n = 20).

Results

PJI specimens exhibited a higher bone volume, thickened trabeculae, and increased osteoid parameters compared to both control groups, suggesting an accelerated bone turnover with sclerotic microstructure. On the cellular level, osteoblast and osteoclast parameters were markedly increased in the PJI cohort. Furthermore, a positive association between serum (CRP) but not synovial (white blood cell (WBC) count) inflammatory markers and osteoclast indices could be detected. Comparison between different pathogens revealed increased osteoclastic bone resorption parameters without a concomitant increase in osteoblasts in bone specimens from patients with Staphylococcus aureus infection, compared to those with detection of Staphylococcus epidermidis and Cutibacterium spp.

Conclusion

This study provides insights into the local bone metabolism in chronic PJI, demonstrating osteosclerosis with high bone turnover. The fact that Staphylococcus aureus was associated with distinctly increased osteoclast indices strongly suggests early surgical treatment to prevent periprosthetic bone alterations.

Microbial Biofilm: A Review on Formation, Infection, Antibiotic Resistance, Control Measures, and Innovative Treatment

Biofilm is complex and consists of bacterial colonies that reside in an exopolysaccharide matrix that attaches to foreign surfaces in a living organism. Biofilm frequently leads to nosocomial, chronic infections in clinical settings. Since the bacteria in the biofilm have developed antibiotic resistance, using antibiotics alone to treat infections brought on by biofilm is ineffective. This review provides a succinct summary of the theories behind the composition of, formation of, and drug-resistant infections attributed to biofilm and cutting-edge curative approaches to counteract and treat biofilm. The high frequency of medical device-induced infections due to biofilm warrants the application of innovative technologies to manage the complexities presented by biofilm.

The Role of Coagulase-Negative Staphylococci Biofilms on Late-Onset Sepsis: Current Challenges and Emerging Diagnostics and Therapies

Infections are one of the most significant complications of neonates, especially those born preterm, with sepsis as one of the principal causes of mortality. Coagulase-negative staphylococci (CoNS), a group of staphylococcal species that naturally inhabit healthy human skin and mucosa, are the most common cause of late-onset sepsis, especially in preterms. One of the risk factors for the development of CoNS infections is the presence of implanted biomedical devices, which are frequently used for medications and/or nutrient delivery, as they serve as a scaffold for biofilm formation. The major concerns related to CoNS infections have to do with the increasing resistance to multiple antibiotics observed among this bacterial group and biofilm cells’ increased tolerance to antibiotics. As such, the treatment of CoNS biofilm-associated infections with antibiotics is increasingly challenging and considering that antibiotics remain the primary form of treatment, this issue will likely persist in upcoming years. For that reason, the development of innovative and efficient therapeutic measures is of utmost importance. This narrative review assesses the current challenges and emerging diagnostic tools and therapies for the treatment of CoNS biofilm-associated infections, with a special focus on late-onset sepsis.

Microbially-derived cocktail of carbohydrases as an anti-biofouling agents: a 'green approach'

Enzymes, also known as biocatalysts, display vital properties like high substrate specificity, an eco-friendly nature, low energy inputs, and cost-effectiveness. Among their numerous known applications, enzymes that can target biofilms or their components are increasingly being investigated for their anti-biofouling action, particularly in healthcare, food manufacturing units and environmental applications. Enzymes can target biofilms at different levels like during the attachment of microorganisms, formation of exopolymeric substances (EPS), and their disruption thereafter. In this regard, a consortium of carbohydrases that can target heterogeneous polysaccharides present in the EPS matrix may provide an effective alternative to conventional chemical anti-biofouling methods. Further, for complete annihilation of biofilms, enzymes can be used alone or in conjunction with other antimicrobial agents. Enzymes hold the promise to replace the conventional methods with greener, more economical, and more efficient alternatives. The present article explores the potential and future perspectives of using carbohydrases as effective anti-biofilm agents.

Multi-epitope based vaccine design against Staphylococcus epidermidis: A subtractive proteomics and immunoinformatics approach

Staphylococcus epidermidis has emerged as a major contributor of nosocomial infections across the world. With the increased rate of emerging resistant and previously undefined infectious diseases, there is a growing need to develop a novel vaccine possessing required immunogenic properties. The adopted reverse vaccinology approach identified "IMPNQILTI" of LysM domain protein, "YSYTYTIDA" of staphylococcal secretory antigen SsaA, and "YNYDANTGQ" neutral metalloproteinaseas potential peptides for vaccine design. The 9-mer epitope of target proteins is antigenic, virulent, surface-exposed, non-allergenic, and conserved across various strains of S. epidermidis. Protein-protein interactions study indicated the involvement of target proteins in major biological pathways for S. epidermidis pathogenesis. Protein-peptide docking was performed, and population coverage analysis showed significant interactions of T-cell epitopes with the HLA-binding molecules while covering 90.58% of the world's population. Further, a multi-epitope vaccine of 177 amino acids long was constructed. Docking with Toll-like receptor (TLR-2) molecule confirmed the effective interaction of the vaccine with the receptor. The vaccine efficiency in generating an effective immune response in the host was evaluated by immune simulation. Finally, in silico cloning confirmed that the constructed vaccine can be efficiently expressed in E. coli. However, the designed vaccine needs experimental validation to determine the effectiveness and immunogenicity profile, which will ensure an active immunity against S. epidermidis.

Mimicking biofilm formation and development: Recent progress in in vitro and in vivo biofilm models

Biofilm formation in living organisms is associated to tissue and implant infections, and it has also been linked to the contribution of antibiotic resistance. Thus, understanding biofilm development and being able to mimic such processes is vital for the successful development of antibiofilm treatments and therapies. Several decades of research have contributed to building the foundation for developing in vitro and in vivo biofilm models. However, no such thing as an "all fit" in vitro or in vivo biofilm models is currently available. In this review, in addition to presenting an updated overview of biofilm formation, we critically revise recent approaches for the improvement of in vitro and in vivo biofilm models.

Osteointegration, antimicrobial and antibiofilm activity of orthopaedic titanium surfaces coated with silver and strontium-doped hydroxyapatite using a novel blasting process

Poor integration of orthopaedic devices with the host tissue owing to aseptic loosening and device-associated infections are two of the leading causes of implant failure, which represents a significant problem for both patients and the healthcare system. Novel strategies have focused on silver to combat antimicrobial infections as an alternative to drug therapeutics. In this study, we investigated the impact of increasing the % substitution (12% wt) of silver and strontium in hydroxyapatite (HA) coatings to enhance antimicrobial properties and stimulate osteoblasts, respectively. Additionally, we prepared a binary substituted coating containing both silver and strontium (AgSrA) at 12% wt as a comparison. All coatings were deposited using a novel blasting process, CoBlast, onto biomedical grade titanium (V). Surface physicochemical properties, cytocompatibility and antimicrobial functionality were determined. The anticolonising properties of the coatings were screened using Staphylococcus aureus ATCC 1448, and thereafter, the AgA coating was evaluated using clinically relevant strains. Strontium-doped surfaces demonstrated enhanced osteoblast viability; however, a lower inhibition of biofilm formation was observed compared with the other surfaces. A co-substituted AgSrA surface did not show enhanced osteoblast or anticolonising properties compared with the SrA and AgA surfaces, respectively. Due to its superior anticolonising performance in preliminary studies, AgA was chosen for further studies. The AgA coated surfaces demonstrated good antibacterial activity (eluted and immobilised ion) against methicillin-resistant S. aureus followed by methicillin-sensitive Staphylococcus aureus clinical isolates; however, the AgA surface displayed poor impact against Staphylococcus epidermidis. In conclusion, herein, we demonstrate that HA can be substituted with a range of ions to augment the properties of HA coatings on orthopaedic devices, which offer promising potential to combat orthopaedic device-associated infections and enhance device performance.

The staphylococcal exopolysaccharide PIA - Biosynthesis and role in biofilm formation, colonization, and infection

Exopolysaccharide is a key part of the extracellular matrix that contributes to important mechanisms of bacterial pathogenicity, most notably biofilm formation and immune evasion. In the human pathogens Staphylococcus aureus and S. epidermidis, as well as in many other staphylococcal species, the only exopolysaccharide is polysaccharide intercellular adhesin (PIA), a cationic, partially deacetylated homopolymer of N-acetylglucosamine, whose biosynthetic machinery is encoded in the ica locus. PIA production is strongly dependent on environmental conditions and controlled by many regulatory systems. PIA contributes significantly to staphylococcal biofilm formation and immune evasion mechanisms, such as resistance to antimicrobial peptides and ingestion and killing by phagocytes, and presence of the ica genes is associated with infectivity. Due to its role in pathogenesis, PIA has raised considerable interest as a potential vaccine component or target.

The staphylococcal exopolysaccharide PIA - Biosynthesis and role in biofilm formation, colonization, and infection

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PIA is a key extracellular matrix component in staphylococci and other bacteria.

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PIA is a cationic, partially deacetylated N-acetylglucosamine polymer.

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PIA has a major role in bacterial biofilms and biofilm-associated infection.

Exopolysaccharide is a key part of the extracellular matrix that contributes to important mechanisms of bacterial pathogenicity, most notably biofilm formation and immune evasion. In the human pathogens Staphylococcus aureus and S. epidermidis, as well as in many other staphylococcal species, the only exopolysaccharide is polysaccharide intercellular adhesin (PIA), a cationic, partially deacetylated homopolymer of N-acetylglucosamine, whose biosynthetic machinery is encoded in the ica locus. PIA production is strongly dependent on environmental conditions and controlled by many regulatory systems. PIA contributes significantly to staphylococcal biofilm formation and immune evasion mechanisms, such as resistance to antimicrobial peptides and ingestion and killing by phagocytes, and presence of the ica genes is associated with infectivity. Due to its role in pathogenesis, PIA has raised considerable interest as a potential vaccine component or target.

Mini-review: from in vitro to ex vivo studies: an overview of alternative methods for the study of medical biofilms

Microbial biofilms are a natural adaptation of microorganisms, typically composed of multiple microbial species, exhibiting complex community organization and cooperation. Biofilm dynamics and their complex architecture are challenging for basic analyses, including the number of viable cells, biomass accumulation, biofilm morphology, among others. The methods used to study biofilms range from in vitro techniques to complex in vivo models. However, animal welfare has become a major concern, not only in society, but also in the academic and scientific field. Thus, the pursuit for alternatives to in vivo biofilm analyses presenting characteristics that mimic in vivo conditions has become essential. In this context, the present review proposes to provide an overview of strategies to study biofilms of medical interest, with emphasis on alternatives that approximate experimental conditions to host-associated environments, such as the use of medical devices as substrata for biofilm formation, microcosm and ex vivo models.

Transcriptional regulation of virulence factors Hla and phenol-soluble modulins α by AraC-type regulator Rbf in Staphylococcus aureus

Staphylococcus aureus is a gram-positive pathogenic bacterium and is capable of secreting numerous toxins interfering directly with the host to cause acute infections. Rbf, a transcriptional regulator of AraC/XylS family, has been reported to promote biofilm formation in polysaccharide intercellular adhesion (PIA) mediated manner to cause chronic infections. In this study, we revealed the new virulence-mediated role of Rbf that can negatively regulate the hemolytic activity. Furthermore, Rbf can specifically bind to the hla and psmα promoters to repress their expression, resulting in significantly decreased production of phenol-soluble modulins α (PSMα) and alpha-toxin. Accordingly, the rbf mutant strain exhibited the increased pathogenicity compared to the wild-type (WT) strain in a mouse subcutaneous abscess model, representing a type of acute infection by S. aureus. Collectively, our results provide a novel insight into the virulence regulation and acute infections mediated by Rbf in S. aureus.

Kinetic of Adhesion of S. epidermidis with Different EPS Production on Ti6Al4V Surfaces

Controlling initial bacterial adhesion is essential to prevent biofilm formation and implant-related infection. The search for surface coatings that prevent initial adhesion is a powerful strategy to obtain implants that are more resistant to infection. Tracking the progression of adhesion on surfaces from the beginning of the interaction between bacteria and the surface provides a deeper understanding of the initial adhesion behavior. To this purpose, we have studied the progression over time of bacterial adhesion from a laminar flow of a bacterial suspension, using a modified Robbins device (MRD). Comparing with other laminar flow devices, such as the parallel plate flow chamber, MRD allows the use of diverse substrata under the same controlled flow conditions simultaneously. Two different surfaces of Ti6Al4V and two strains of Staphylococcus epidermidis with different exopolymer production were tested. In addition, the modified Robbins device was examined for its convenience and suitability for the purpose of this study. Results were analyzed according to a pseudofirst order kinetic. The values of the parameters obtained from this model make it possible to discriminate the adhesive behavior of surfaces and bacteria. One of the fitting parameters depends on the bacterial strain and the other only on the surface properties of the substrate.

Pharmacokinetic and toxicodynamic evaluation of 5-fluorouracil administration after major hepatectomy in a rat model

BACKGROUND

Chemotherapy after hepatectomy for colorectal liver metastasis has not been established, due to the toxic side effects, which are likely related to impaired drug clearance during liver regeneration. We investigated the pharmacokinetic and toxicodynamic evaluation of 5-fluorouracil (5-FU) during liver regeneration after major hepatectomy in a rat model.

METHODS

Thirty-six male Wistar rats were divided into control (C), control with chemotherapy (CC), hepatectomy (H), and hepatectomy with chemotherapy (HC) groups. The CC and HC groups were administered 5-FU for 4 days. Plasma 5-FU, liver weight, and liver dihydropyrimidine dehydrogenase (DPD) were measured. The ileal villous height was measured to determine adverse effects.

RESULTS

The area under the curve and maximum plasma concentration of 5-FU increased by up to 51% and 32%, respectively, in the HC group compared to the CC group. The liver regeneration rate was significantly lower in the HC group than in the H group (67.3 ± 7.4 vs 33.0 ± 5.7%, p < 0.001). The HC group had a significantly lower liver DPD than the CC group (4.4 ± 1.1 mg vs 6.9 ± 1.1 mg, p < 0.01). The HC group had a significantly lower ileal villous height than the CC group (253 ± 40 μm vs. 318 ± 36 μm, p < 0.05).

CONCLUSIONS

Reduction of the total liver DPD following major hepatectomy caused increased plasma 5-FU levels and 5-FU-associated toxicity.

Antibiofilm Synergy of β-Lactams and Branched Polyethylenimine against Methicillin-Resistant Staphylococcus epidermidis

Microbial biofilms are ubiquitous in nature, and they pose a serious threat to public health. Staphylococcus epidermidis is the most common clinical isolate from healthcare- and medical device-related biofilm infections. No antibiotic currently on the market can eradicate pathogenic biofilms, which contain complex defense mechanisms composed of slimelike extracellular polymeric substances. Understanding the need to develop alternative approaches, we examine 600 Da branched polyethylenimine (BPEI) against methicillin-resistant Staphylococcus epidermidis (MRSE) biofilms. Here, a microtiter biofilm model is used to test the synergistic effects between the two components of our combination treatment: BPEI and β-lactam antibiotics. Electron microscopy was used to confirm the growth of MRSE biofilms from the model. Minimum biofilm eradication concentration assays, crystal violet assays, and biofilm kill curves suggest that BPEI exhibits antibiofilm activity and can potentiate β-lactams to eradicate MRSE biofilms.

Role of Phenol-Soluble Modulins in Staphylococcus epidermidis Biofilm Formation and Infection of Indwelling Medical Devices

Phenol-soluble modulins (PSMs) are amphipathic, alpha-helical peptides that are secreted by staphylococci in high amounts in a quorum-sensing-controlled fashion. Studies performed predominantly in Staphylococcus aureus showed that PSMs structure biofilms, which results in reduced biofilm mass, while it has also been reported that S. aureus PSMs stabilize biofilms due to amyloid formation. We here analyzed the roles of PSMs in in vitro and in vivo biofilms of Staphylococcus epidermidis, the leading cause of indwelling device-associated biofilm infection. We produced isogenic deletion mutants for every S. epidermidis psm locus and a sequential deletion mutant in which production of all PSMs was abolished. In vitro analysis substantiated the role of all PSMs in biofilm structuring. PSM-dependent biofilm expansion was not observed, in accordance with our finding that no S. epidermidis PSM produced amyloids. In a mouse model of indwelling device-associated infection, the total psm deletion mutant had a significant defect in dissemination. Notably, the total psm mutant produced a significantly more substantial biofilm on the implanted catheter than the wild-type strain. Our study, which for the first time directly quantified the impact of PSMs on biofilm expansion on an implanted device, shows that the in vivo biofilm infection phenotype in S. epidermidis is in accordance with the PSM biofilm structuring and detachment model, which has important implications for the potential therapeutic application of quorum-sensing blockers.

Transcriptional Regulation of icaADBC by both IcaR and TcaR in Staphylococcus epidermidis

S. epidermidis is a primary cause of biofilm-mediated infections in humans due to adherence to foreign bodies. A major staphylococcal biofilm accumulation molecule is polysaccharide intracellular adhesin (PIA), which is synthesized by enzymes encoded by the icaADBC operon. Expression of PIA is highly variable among clinical isolates, suggesting that PIA expression levels are selected in certain niches of the host. However, the mechanisms that govern enhanced icaADBC transcription and PIA synthesis in these isolates are not known. We hypothesized that enhanced PIA synthesis in these isolates was due to function of IcaR and/or TcaR. Thus, two S. epidermidis isolates (1457 and CSF41498) with different icaADBC transcription and PIA expression levels were studied. Constitutive expression of both icaR and tcaR demonstrated that both repressors are functional and can completely repress icaADBC transcription in both 1457 and CSF41498. However, it was found that IcaR was the primary repressor for CSF41498 and TcaR was the primary repressor for 1457. Further analysis demonstrated that icaR transcription was repressed in 1457 in comparison to CSF41498, suggesting that TcaR functions as a repressor only in the absence of IcaR. Indeed, DNase I footprinting suggests IcaR and TcaR may bind to the same site within the icaR-icaA intergenic region. Lastly, we found mutants expressing variable amounts of PIA could rapidly be selected from both 1457 and CSF41498. Collectively, we propose that strains producing enhanced PIA synthesis are selected within certain niches of the host through several genetic mechanisms that function to repress icaR transcription, thus increasing PIA synthesis.IMPORTANCE Staphylococcus epidermidis is a commensal bacterium that resides on our skin. As a commensal, it protects humans from bacterial pathogens through a variety of mechanisms. However, it is also a significant cause of biofilm infections due to its ability to bind to plastic. Polysaccharide intercellular adhesin is a significant component of biofilm, and we propose that the expression of this polysaccharide is beneficial in certain host niches, such as providing extra strength when the bacterium is colonizing the lumen of a catheter, and detrimental in others, such as colonization of the skin surface. We show here that fine-tuning of icaADBC transcription, and thus PIA synthesis, is mediated via two transcriptional repressors, IcaR and TcaR.

Staphylococcal Biofilms

Staphylococci, with the leading species Staphylococcus aureus and Staphylococcus epidermidis, are the most frequent causes of infections on indwelling medical devices. The biofilm phenotype that those bacteria adopt during device-associated infection facilitates increased resistance to antibiotics and host immune defenses. This review presents and discusses the molecular mechanisms contributing to staphylococcal biofilm development and their in-vivo importance. Furthermore, it summarizes current strategies for the development of therapeutics against staphylococcal biofilm-associated infection.

Comparison of Microbiological Examination by Test Tube and Congo Red Agar Methods to Detect Biofilm Production on Clinical Isolates

Biofilm on medical devices can cause significant diseases and deaths and give a large effecton disease transmission among patients and health providers and potentially increasethe cost of patient treatment. By knowing the presence of biofilm on a patient, one can differentiate the treatment management for that particular patient from the patients without biofilm on their medical device. The purpose of this study was to obtain diagnostic method to detect biofilm formation on isolates from the medical devices by simple method that is easy to do and can be applied in resource-limited microbiology laboratory. 36 specimens obtained from IV Line, CVC, urinary catheter and ETT were grown on Muller Hinton agar and continued with 3 methods, i.e., Test Tube method, Congo Red Agar method and Microtiter Plate Assay method. Results of this study showed Test Tube (nephelometer), Test Tube (visual) and Congo Red Agar in order to have the same sensitivity of 100% but has higher specificity compared to Test Tube method (visual) and Congo Red Agar method in detecting biofilm production on isolates from medical devices that had been plugged into patients body. The biofilm formation inside devices depends on factors, i.e., host, device and the microorganism itself.

Immune Evasion Mechanisms of Staphylococcus epidermidis Biofilm Infection

The primary virulence factor of the skin commensal and opportunistic pathogen, Staphylococcus epidermidis, is the ability to form biofilms on surfaces of implanted materials. Much of this microorganism’s pathogenic success has been attributed to its ability to evade the innate immune system. The primary defense against S. epidermidis biofilm infection consists of complement activation, recruitment and subsequent killing of the pathogen by effector cells. Among pathogen-derived factors, the biofilm exopolysaccharide polysaccharide intercellular adhesion (PIA), as well as the accumulation-associated protein (Aap), and the extracellular matrix binding protein (Embp) have been shown to modulate effector cell-mediated killing of S. epidermidis. Phenol-soluble modulins (PSMs) constitute the only class of secreted toxins by S. epidermidis, at least one type of which (PSMδ) possesses strong cytolytic properties toward leukocytes. However, through selective production of non-cytolytic subtypes of PSMs, S. epidermidis is able to maintain a low inflammatory infection profile and avoid eradication by the host immune system. Taken together, our emerging understanding of the mechanisms behind immune modulation by S. epidermidis elucidates the microorganism’s success in the initial colonization of device surfaces as well as the maintenance of a chronic and indolent course of biofilm infection.

Comparative analysis between biofilm formation and gene expression in Staphylococcus epidermidis isolates

AIM

To understand the relationship between ica, aap and bhp gene expression and the implications in biofilm formation in selected clinical and commensal Staphylococcus epidermidis isolates.

MATERIAL & METHODS

Isolates were analyzed regarding their biofilm-forming capacity, biochemical matrix composition, biofilm spatial organization and expression of biofilm-related genes.

RESULTS

On polysaccharide intercellular adhesin-dependent biofilms, aap and bhp contributions for the biofilm growth were negligible, despite very high levels of expression. In contrast, smaller increases in icaA expression contributed significantly to biofilm growth. Interestingly, no biological differences were observed between clinical and commensal strains.

CONCLUSION

These results reinforce the concept that S. epidermidis is an 'accidental pathogen,' and that the ica operon is the main mechanism of biofilm formation in clinical and commensal isolates.

Advances in in Vitro and in Vivo Models for Studying the Staphylococcal Factors Involved in Implant Infections

Implant infections due to staphylococci are one of the greatest threats facing patients receiving implant devices. For many years researchers have sought to understand the mechanisms involved in the adherence of the bacterium to the implanted device and the formation of the unique structure, the biofilm, which protects the indwelling bacteria from the host defence and renders them resistant to antibiotic treatment. A major goal has been to develop in vitro and in vivo models that adequately reflect the real-life situation. From the simple microtiter plate assay and scanning electron microscopy, tools for studying adherence and biofilm formation have since evolved to include specialised equipment for studying adherence, flow cell systems, real-time analysis of biofilm formation using reporter gene assays both in vitro and in vivo, and a wide variety of animal models. In this article, we discuss advances in the last few years in selected in vitro and in vivo models as well as future developments in the study of adherence and biofilm formation by the staphylococci.

Modern Strategies in the Prevention of Implant-Associated Infections

The application of medical devices either for temporary or permanent use has become an indispensible part of almost all fields of medicine. However, foreign bodies are associated with a substantial risk of bacterial and fungal infections. Implant-associated infections significantly contribute to the still increasing problem of nosocomial infections.

To reduce the incidence of such infections, specific guidelines providing evidence-based recommendations and comprising both technological and nontechnological strategies for prevention have been established. Strict adherence to hygienic rules during insertion or implantation of the device are aspects of particular importance. Besides such basic and indispensable aspects, the development of new materials which could withstand microbial adherence and colonization has become a major topic in recent years. Modification of surface by primarily physico-chemical methods may lead to a change in specific and unspecific interactions with microorganisms and, thus, to a reduction in microbial adherence. Medical devices made out of a material that would be ideally antiadhesive or at least colonization-resistant would be the most suitable candidates to avoid colonization and subsequent infection. However, it appears impossible to create a surface with an absolute “zero”-adherence due to thermodynamical reasons and due to the fact that a modified material surface is in vivo rapidly covered by plasma and connective tissue proteins. Therefore, another concept for the prevention of implant-associated infections involves the impregnation of devices with various antimicrobial substances such as antibiotics, antiseptics, and/or metals.

In fact, already commercially available materials for clinical use such as antimicrobial catheters have been introduced, in part with considerable impact on subsequent infections. However, future studies are warranted to translate the knowledge on the pathogenesis of device-associated infections into applicable prevention strategies.

Molecular Genetics of Staphylococcus Epidermidis Biofilms on Indwelling Medical Devices

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

Biofilm Formation is not Necessary for Development of Quinolone-Resistant “Persister” cells in an Attached Staphylococcus Epidermidis Population

Staphylococcus epidermidis is a common pathogen in device-associated infections which is able to attach onto polymeric surfaces and develop multilayered biofilms. Attached S. epidermidis displays reduced susceptibility to antimicrobial agents. In this study we investigated the influence of ciprofloxacin and the group IV quinolones gatifloxacin, gemifloxacin, and moxifloxacin with the minimal attachment killing (MAK) assay. MAK concentrations were determined for three biofilm-positive wild-type strains and their isogenic biofilm-negative mutants Depending on strain and investigated quinolone, it was possible to distinguish between a heterogeneous MAK (MAKhetero), and a homogeneous resistance (MAKhomo) which corresponds to the model of a few persisting cells under antibiotic treatment. A lower MAKhomo was detected for the biofilm-negative mutants as well as for the corresponding wild-types for some of the tested quinolones, which seems to be a result of higher bacterial inocula, whereas the MAKhetero concentrations were comparable for mutants and wild-types for nearly all of the tested antibiotics and strains. These data indicate that biofilm formation is not necessary for persistence of attached S. epidermidis cells under treatment with quinolones and could explain therapeutic failure in foreign body-associated infections due to biofilm-negative S. epidermidis isolates. The individual resistance phenotypes of investigated strains indicate that the determination of MAK concentrations might help to predict the therapy outcome of foreign body-associated infections with both biofilm-positive and biofilm-negative S. epidermidis. Thus, the relatively high activity displayed by group IV quinolones against individual attached staphylococcal isolates indicates a possible treatment option with the respective quinolones for foreign body-associated infections due to these isolates. (Int J Artif Organs 2008; 31: 752–60)

Microbial biofilm in human health - an updated theoretical and practical insight

The term biofilm designates an aggregate of microorganisms belonging to one or more species which adhere to various surfaces but also to each another. These microbial communities are included and interconnected within an organic structure known as slime, composed of protein substances, polysaccharides, and DNA.

The Center for Disease prevention and control considers infections with bacteria in biofilms among the 7 most important challenges which must be overcome in order to improve the safety of health services. The risk of microbial biofilm development exists for a long list of medical devices and equipment, as well as in certain diseases such as cystic fibrosis. An aggravating aspect is represented by the almost 1,000 times higher antimicrobial resistance of bacteria growing and multiplying within biofilms. Thus, in case of biofilm-infected medical devices, the resistance to antimicrobial treatments requires the removal of the device which essentially means the failure of the exploratory or therapeutic intervention in question.

The role of microbial biofilms in medical pathology is a subject that raises interest for both researchers and clinicians in order to establish new methods for prevention and treatment of biofilms. This paper is intended as an overview in the management of microbial biofilms, presenting future insights, with technological progress in microscopy, molecular genetics, and genome analysis. Therefore the present paper will focus on describing the mechanisms involved in biofilm development, biofilm related infections, methods of detection and quantification of microbial communities and therapeutical approaches.

Poly-N-Acetylglucosamine Production by Staphylococcus epidermidis Cells Increases Their In Vivo Proinflammatory Effect

Poly-N-acetylglucosamine (PNAG) is a major component of the Staphylococcus epidermidis biofilm extracellular matrix. However, it is not yet clear how this polysaccharide impacts the host immune response and infection-associated pathology. Faster neutrophil recruitment and bacterial clearance were observed in mice challenged intraperitoneally with S. epidermidis biofilm cells of the PNAG-producing 9142 strain than in mice similarly challenged with the isogenic PNAG-defective M10 mutant. Moreover, intraperitoneal priming with 9142 cells exacerbated liver inflammatory pathology induced by a subsequent intravenous S. epidermidis challenge, compared to priming with M10 cells. The 9142-primed mice had elevated splenic CD4(+) T cells producing gamma interferon and interleukin-17A, indicating that PNAG promoted cell-mediated immunity. Curiously, despite having more marked liver tissue pathology, 9142-primed mice also had splenic T regulatory cells with greater suppressive activity than those of their M10-primed counterparts. By showing that PNAG production by S. epidermidis biofilm cells exacerbates host inflammatory pathology, these results together suggest that this polysaccharide contributes to the clinical features associated with biofilm-derived infections.

Sub-inhibitory tigecycline concentrations induce extracellular matrix binding protein Embp dependent Staphylococcus epidermidis biofilm formation and immune evasion

Biofilm-associated Staphylococcus epidermidis implant infections are notoriously reluctant to antibiotic treatment. Here we studied the effect of sub-inhibitory concentrations of penicillin, oxacillin, vancomycin, daptomycin, linezolid and tigecycline on S. epidermidis 1585 biofilm formation, expression of extracellular matrix binding protein (Embp) and potential implications for S. epidermidis - macrophage interactions. Penicillin, vancomycin, daptomycin, and linezolid had no biofilm augmenting effect at any of the concentrations tested. In contrast, at sub-inhibitory concentrations tigecycline and oxacillin exhibited significant biofilm inducing activity. In S. epidermidis 1585, SarA is a negative regulator of giant 1 MDa Embp, and down regulation of sarA induces Embp-dependent assembly of a multi-layered biofilm architecture. Dot blot immune assays, confocal laser scanning microscopy, and qPCR showed that under biofilm inducing conditions, tigecycline augmented embp expression compared to the control grown without antibiotics. Conversely, expression of regulator sarA was suppressed, suggesting that tigecycline exerts its effects on embp expression through SarA. Tigecycline failed to induce biofilm formation in embp transposon mutant 1585-M135, proving that under these conditions Embp up-regulation is necessary for biofilm accumulation. As a functional consequence, tigecycline induced biofilm formation significantly impaired the up-take of S. epidermidis by mouse macrophage-like cell line J774A.1. Our data provide novel evidence for the molecular basis of antibiotic induced biofilm formation, a phenotype associated with inherently increased antimicrobial tolerance. While this could explain failure of antimicrobial therapies, persistence of S. epidermidis infections in the presence of sub-inhibitory antimicrobials is additionally propelled by biofilm-related impairment of macrophage-mediated pathogen eradication.

Bacterial Extracellular Polysaccharides in Biofilm Formation and Function

Microbes produce a biofilm matrix consisting of proteins, extracellular DNA, and polysaccharides that is integral in the formation of bacterial communities. Historical studies of polysaccharides revealed that their overproduction often alters the colony morphology and can be diagnostic in identifying certain species. The polysaccharide component of the matrix can provide many diverse benefits to the cells in the biofilm, including adhesion, protection, and structure. Aggregative polysaccharides act as molecular glue, allowing the bacterial cells to adhere to each other as well as surfaces. Adhesion facilitates the colonization of both biotic and abiotic surfaces by allowing the bacteria to resist physical stresses imposed by fluid movement that could separate the cells from a nutrient source. Polysaccharides can also provide protection from a wide range of stresses, such as desiccation, immune effectors, and predators such as phagocytic cells and amoebae. Finally, polysaccharides can provide structure to biofilms, allowing stratification of the bacterial community and establishing gradients of nutrients and waste products. This can be advantageous for the bacteria by establishing a heterogeneous population that is prepared to endure stresses created by the rapidly changing environments that many bacteria encounter. The diverse range of polysaccharide structures, properties, and roles highlight the importance of this matrix constituent to the successful adaptation of bacteria to nearly every niche. Here, we present an overview of the current knowledge regarding the diversity and benefits that polysaccharide production provides to bacterial communities within biofilms.

AraC-Type Regulator Rsp Adapts Staphylococcus aureus Gene Expression to Acute Infection

Staphylococcus aureus is an important human pathogen that can cause two categories of severe infections. Acute infections are characterized by pronounced toxin production, while chronic infections often involve biofilm formation. However, it is poorly understood how S. aureus controls the expression of genes associated with acute versus biofilm-associated virulence. We here identified an AraC-type transcriptional regulator, Rsp, that promotes the production of key toxins while repressing major biofilm-associated genes and biofilm formation. Genome-wide transcriptional analysis and modeling of regulatory networks indicated that upregulation of the accessory gene regulator (Agr) and downregulation of the ica operon coding for the biofilm exopolysaccharide polysaccharide intercellular adhesin (PIA) were central to the regulatory impact of Rsp on virulence. Notably, the Rsp protein directly bound to the agrP2 and icaADBC promoters, resulting in strongly increased levels of the Agr-controlled toxins phenol-soluble modulins (PSMs) and alpha-toxin and reduced production of PIA. Accordingly, Rsp was essential for the development of bacteremia and skin infection, representing major types of acute S. aureus infection. Our findings give important insight into how S. aureus adapts the expression of its broad arsenal of virulence genes to promote different types of disease manifestations and identify the Rsp regulator as a potential target for strategies to control acute S. aureus infection.

Emerging interactions between matrix components during biofilm development

Bacterial cells are most often found in the form of multicellular aggregates commonly referred to as biofilms. Biofilms offer their member cells several benefits, such as resistance to killing by antimicrobials and predation. During biofilm formation there is a production of extracellular substances that, upon assembly, constitute an extracellular matrix. The ability to generate a matrix encasing the microbial cells is a common feature of biofilms, but there is diversity in matrix composition and in interaction between matrix components. The different components of bacterial biofilm extracellular matrixes, known as matrix interactions, and resulting implications are discussed in this review.

Effects of polysaccharide intercellular adhesin (PIA) in an ex vivo model of whole blood killing and in prosthetic joint infection (PJI): A role for C5a

BACKGROUND

A major complication of using medical devices is the development of biofilm-associated infection caused by Staphylococcus epidermidis where polysaccharide intercellular adhesin (PIA) is a major mechanism of biofilm accumulation. PIA affects innate and humoral immunity in isolated cells and animal models. Few studies have examined these effects in prosthetic joint infection (PJI).

METHODS

This study used ex vivo whole blood modelling in controls together with matched-serum and staphylococcal isolates from patients with PJI.

RESULTS

Whole blood killing of PIA positive S. epidermidis and its isogenic negative mutant was identical. Differences were unmasked in immunosuppressed whole blood pre-treated with dexamethasone where PIA positive bacteria showed a more resistant phenotype. PIA expression was identified in three unique patterns associated with bacteria and leukocytes, implicating a soluble form of PIA. Purified PIA reduced whole blood killing while increasing C5a levels. In clinically relevant staphylococcal isolates and serum samples from PJI patients; firstly complement C5a was increased 3-fold compared to controls; secondly, the C5a levels were significantly higher in serum from PJI patients whose isolates preferentially formed PIA-associated biofilms.

CONCLUSIONS

These data demonstrate for the first time that the biological effects of PIA are mediated through C5a in patients with PJI.

Evaluation of Ica Gene in Comparison with Phenotypic Methods for Detection of Biofilm Production by Coagulase Negative Staphylococci in a Tertiary Care Hospital

BACKGROUND

Biofilm producing bacteria are responsible for several chronic infections and are difficult to treat as they show much greater resistance to antibiotics. The major virulence factor determining the pathogenicity of CoNS has now well defined and found to be biofilm production.

OBJECTIVE

The study was conducted to isolate and characterize Coagulase Negative Staphylococci (CoNS) and their ability to form biofilms was evaluated by phenotypic and genotypic methods.

MATERIALS AND METHODS

A total of 96 clinical isolates of CoNS were characterized and subjected to biofilm detection by tissue culture plate method (TCP), tube method (TM), congo red agar method (CRA) and PCR.

RESULTS

Staphylococcus epidermidis was the most commonly isolated species 76(79.17%). The ica gene was present in 35 (36.45%) of CoNS isolates which were detected as biofilm producers by TCP. Biofilm producing isolates showed higher antibiotic resistance(72.1%). Majority of biofilm producers had strong association with medical device related infections.

CONCLUSION

To compare PCR based dectection method for presence of ica genes with TCP, the test share the specific identification rates. The sensitivity and specificity of TCP method in detection of biofilm was high in comparison with TM and CRA. TCP can be recommended as a general screening test for biofilm detection.

A Commensal Strain of Staphylococcus epidermidis Overexpresses Membrane Proteins Associated with Pathogenesis When Grown in Biofilms

Staphylococcus epidermidis has emerged as one of the major nosocomial pathogens associated with infections of implanted medical devices. The most important factor in the pathogenesis of these infections is the formation of bacterial biofilms. Bacteria grown in biofilms are more resistant to antibiotics and to the immune defence system than planktonic bacteria. In these infections, the antimicrobial therapy usually fails and the removal of the biofilm-coated implanted device is the only effective solution. In this study, three proteomic approaches were performed to investigate membrane proteins associated to biofilm formation: (i) sample fractionation by gel electrophoresis, followed by isotopic labelling and LC-MS/MS analysis, (ii) in-solution sample preparation, followed by isotopic labelling and LC-MS/MS analysis and (iii) in-solution sample preparation and label-free LC-MS/MS analysis. We found that the commensal strain S. epidermidis CECT 231 grown in biofilms expressed higher levels of five membrane and membrane-associated proteins involved in pathogenesis: accumulation-associated protein, staphylococcal secretory antigen, signal transduction protein TRAP, ribonuclease Y and phenol soluble modulin beta 1 when compared with bacteria grown under planktonic conditions. These results indicate that a commensal strain can acquire a pathogenic phenotype depending on the mode of growth.

The role of microbial biofilms in prosthetic joint infections

Prosthetic joint infection (PJI) still remains a significant problem. In line with the forecasted rise in joint replacement procedures, the number of cases of PJI is also anticipated to rise. The formation of biofilm by causative pathogens is central to the occurrence and the recalcitrance of PJI. The subject of microbial biofilms is receiving increasing attention, probably as a result of the wide acknowledgement of the ubiquity of biofilms in the natural, industrial, and clinical contexts, as well as the notorious difficulty in eradicating them. In this review, we discuss the pertinent issues surrounding PJI and the challenges posed by biofilms regarding diagnosis and treatment. In addition, we discuss novel strategies of prevention and treatment of biofilm-related PJI.

An 18 kDa scaffold protein is critical for Staphylococcus epidermidis biofilm formation

Virulence of the nosocomial pathogen Staphylococcus epidermidis is crucially linked to formation of adherent biofilms on artificial surfaces. Biofilm assembly is significantly fostered by production of a bacteria derived extracellular matrix. However, the matrix composition, spatial organization, and relevance of specific molecular interactions for integration of bacterial cells into the multilayered biofilm community are not fully understood. Here we report on the function of novel 18 kDa Small basic protein (Sbp) that was isolated from S. epidermidis biofilm matrix preparations by an affinity chromatographic approach. Sbp accumulates within the biofilm matrix, being preferentially deposited at the biofilm–substratum interface. Analysis of Sbp-negative S. epidermidis mutants demonstrated the importance of Sbp for sustained colonization of abiotic surfaces, but also epithelial cells. In addition, Sbp promotes assembly of S. epidermidis cell aggregates and establishment of multilayered biofilms by influencing polysaccharide intercellular-adhesin (PIA) and accumulation associated protein (Aap) mediated intercellular aggregation. While inactivation of Sbp indirectly resulted in reduced PIA-synthesis and biofilm formation, Sbp serves as an essential ligand during Aap domain-B mediated biofilm accumulation. Our data support the conclusion that Sbp serves as an S. epidermidis biofilm scaffold protein that significantly contributes to key steps of surface colonization. Sbp-negative S. epidermidis mutants showed no attenuated virulence in a mouse catheter infection model. Nevertheless, the high prevalence of sbp in commensal and invasive S. epidermidis populations suggests that Sbp plays a significant role as a co-factor during both multi-factorial commensal colonization and infection of artificial surfaces.

Biofilm formation is a key phenotype allowing the otherwise harmless skin commensal S. epidermidis to establish chronic implant-associated infections, affecting millions of patients worldwide. S. epidermidis biofilm assembly relies on the production of an extracellular matrix that serves as glue to stabilize the multilayered bacterial architecture. Here we identified novel 18 kDa Small basic protein (Sbp) as a key component of the extracellular matrix that promotes pivotal steps of bacterial biofilm formation in vitro. Importantly, Sbp is deposited specifically at the interface between biofilm and substrate, as well as in larger humps interspersed within the bacterial cell architecture, thereby forming a proteinaceous biofilm scaffold. This localization enables Sbp to foster stable S. epidermidis interactions with an artificial surface and also contributes to S. epidermidis cell aggregation mechanisms, i.e., polysaccharide intercellular adhesin (PIA) and accumulation associated protein (Aap). In fact, by demonstrating direct Sbp-Aap interactions we provide the first evidence supporting the idea that specific molecular interactions between S. epidermidis and matrix components are involved in S. epidermidis biofilm accumulation. In conclusion, we here show that Sbp promotes key phenotypic features important for S. epidermidis to evolve as an opportunistic pathogen.

An immunoproteomic approach for characterization of dormancy within Staphylococcus epidermidis biofilms

Virulence of Staphylococcus epidermidis is mainly attributed to surface colonization and biofilm formation in indwelling medical devices. Physiological heterogeneity of biofilms may influence host immune response and sensitivity to antibiotics. Dormant cells, among others, contribute to biofilm heterogeneity. The aim of this study was to identify immunogenic proteins of S. epidermidis biofilms associated with dormancy mechanism, by using two-dimensional electrophoresis (2-DE) immunoblotting and mass spectrometry (MS). A total of 19 bacterial proteins, recognized by human serum samples, were identified. These proteins were mainly involved in small molecule metabolic biological processes. Catalytic activity and ion binding were the most representative molecular functions. CodY and GpmA proteins were more reactive to sera when biofilm dormancy was induced, while FtnA and ClpP were more reactive when dormancy was prevented. This is the first work that identifies differences in immunoreactive proteins within bacterial biofilms with induced or prevented dormancy. Considering the importance of dormancy within biofilms, further evaluation of these proteins can provide insights into the mechanisms related to dormancy and help to improve current understanding on how dormancy affects the host immune response.

Role of exopolysaccharide in Aggregatibacter actinomycetemcomitans-induced bone resorption in a rat model for periodontal disease

Aggregatibacter actinomycetemcomitans a causative agent of periodontal disease in humans, forms biofilm on biotic and abiotic surfaces. A. actinomycetemcomitans biofilm is heterogeneous in nature and is composed of proteins, extracellular DNA and exopolysaccharide. To explore the role played by the exopolysaccharide in the colonization and disease progression, we employed genetic reduction approach using our rat model of A. actinomycetemcomitans-induced periodontitis. To this end, a genetically modified strain of A. actinomycetemcomitans lacking the pga operon was compared with the wild-type strain in the rat infection model. The parent and mutant strains were primarily evaluated for bone resorption and disease. Our study showed that colonization, bone resorption/disease and antibody response were all elevated in the wild-type fed rats. The bone resorption/disease caused by the pga mutant strain, lacking the exopolysaccharide, was significantly less (P < 0.05) than the bone resorption/disease caused by the wild-type strain. Further analysis of the expression levels of selected virulence genes through RT-PCR showed that the decrease in colonization, bone resorption and antibody titer in the absence of the exopolysaccharide might be due to attenuated levels of colonization genes, flp-1, apiA and aae in the mutant strain. This study demonstrates that the effect exerted by the exopolysaccharide in A. actinomycetemcomitans-induced bone resorption has hitherto not been recognized and underscores the role played by the exopolysaccharide in A. actinomycetemcomitans-induced disease.

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

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

Polysaccharide intercellular adhesin in biofilm: structural and regulatory aspects

Staphylococcus aureus and Staphylococcus epidermidis are the leading etiologic agents of implant-related infections. Biofilm formation is the main pathogenetic mechanism leading to the chronicity and irreducibility of infections. The extracellular polymeric substances of staphylococcal biofilms are the polysaccharide intercellular adhesin (PIA), extracellular-DNA, proteins, and amyloid fibrils. PIA is a poly-β(1-6)-N-acetylglucosamine (PNAG), partially deacetylated, positively charged, whose synthesis is mediated by the icaADBC locus. DNA sequences homologous to ica locus are present in many coagulase-negative staphylococcal species, among which S. lugdunensis, however, produces a biofilm prevalently consisting of proteins. The product of icaA is an N-acetylglucosaminyltransferase that synthetizes PIA oligomers from UDP-N-acetylglucosamine. The product of icaD gives optimal efficiency to IcaA. The product of icaC is involved in the externalization of the nascent polysaccharide. The product of icaB is an N-deacetylase responsible for the partial deacetylation of PIA. The expression of ica locus is affected by environmental conditions. In S. aureus and S. epidermidis ica-independent alternative mechanisms of biofilm production have been described. S. epidermidis and S. aureus undergo to a phase variation for the biofilm production that has been ascribed, in turn, to the transposition of an insertion sequence in the icaC gene or to the expansion/contraction of a tandem repeat naturally harbored within icaC. A role is played by the quorum sensing system, which negatively regulates biofilm formation, favoring the dispersal phase that disseminates bacteria to new infection sites. Interfering with the QS system is a much debated strategy to combat biofilm-related infections. In the search of vaccines against staphylococcal infections deacetylated PNAG retained on the surface of S. aureus favors opsonophagocytosis and is a potential candidate for immune-protection.

Adequate Disinfection of a Split-Septum Needleless Intravascular Connector with a 5-Second Alcohol Scrub

Objective.

Define optimum vascular catheter connector valve disinfection practices under laboratory and clinical conditions.

Design.

Prospective observational clinical survey and laboratory assessment of disinfection procedures.

Setting.

All adult inpatients at an academic healthcare center.

Methods.

In the clinical setting, contamination of needleless connectors was assessed in 6 weekly prevalence surveys in which the connector valves from central venous catheters (CVCs) in situ were cultured by pressing the connector diaphragm to an agar plate. Before culture, valves were disinfected by scrubbing the diaphragm with a 70% isopropyl alcohol pledget for 0, 5, 10, 15, or 30 seconds. In the laboratory, the diaphragms on 150 unused sterile connector valves were inoculated with 103, 105, or 108colony-forming units ofStaphylococcus epidermidisand allowed to dry. After disinfection of the diaphragms by scrubbing with a 70% isopropyl alcohol pledget for 0, 5, 10, 15, or 30 seconds, the valves were sampled by pressing the diaphragm to an agar plate.

Results.

In the clinical setting, 363 connector valves from patients with CVCs were sampled, and 66.7% of nondisinfected valves revealed bacterial contamination. After 5-second disinfection with an alcohol pledget, only 1 (1.4%) of 71 yielded microbial growth (P< .005). In the laboratory, at the 103and 105inoculum, all connector valves yielded sterile cultures when scrubbed for 5 or more seconds (P< .001). At the 108inoculum, 2 (20%) of 10 connector valves yielded minimal growth ofS. epidermidis.

Conclusions.

A 5-second scrub with a 70% isopropyl alcohol pledget yields adequate disinfection of a split-septum intravascular catheter connector valve under clinical and laboratory conditions.

Polysaccharide intercellular adhesin in biofilm: structural and regulatory aspects

Staphylococcus aureus and Staphylococcus epidermidis are the leading etiologic agents of implant-related infections. Biofilm formation is the main pathogenetic mechanism leading to the chronicity and irreducibility of infections. The extracellular polymeric substances of staphylococcal biofilms are the polysaccharide intercellular adhesin (PIA), extracellular-DNA, proteins, and amyloid fibrils. PIA is a poly-β(1-6)-N-acetylglucosamine (PNAG), partially deacetylated, positively charged, whose synthesis is mediated by the icaADBC locus. DNA sequences homologous to ica locus are present in many coagulase-negative staphylococcal species, among which S. lugdunensis, however, produces a biofilm prevalently consisting of proteins. The product of icaA is an N-acetylglucosaminyltransferase that synthetizes PIA oligomers from UDP-N-acetylglucosamine. The product of icaD gives optimal efficiency to IcaA. The product of icaC is involved in the externalization of the nascent polysaccharide. The product of icaB is an N-deacetylase responsible for the partial deacetylation of PIA. The expression of ica locus is affected by environmental conditions. In S. aureus and S. epidermidis ica-independent alternative mechanisms of biofilm production have been described. S. epidermidis and S. aureus undergo to a phase variation for the biofilm production that has been ascribed, in turn, to the transposition of an insertion sequence in the icaC gene or to the expansion/contraction of a tandem repeat naturally harbored within icaC. A role is played by the quorum sensing system, which negatively regulates biofilm formation, favoring the dispersal phase that disseminates bacteria to new infection sites. Interfering with the QS system is a much debated strategy to combat biofilm-related infections. In the search of vaccines against staphylococcal infections deacetylated PNAG retained on the surface of S. aureus favors opsonophagocytosis and is a potential candidate for immune-protection.

Bacterial skin commensals and their role as host guardians

Recent years' investigations of the co-evolution and functional integration of the human body and its commensal microbiota have disclosed that the microbiome has a major impact on physiological functions including protection against infections, reaction patterns in the immune system, and disposition for inflammation-mediated diseases. Two ubiquitous members of the skin microbiota, the Gram-positive bacteria Staphylococcus epidermidis and Propionibacterium acnes, are predominant on human epithelia and in sebaceous follicles, respectively. Their successful colonisation is a result of a commensal or even mutualistic lifestyle, favouring traits conferring persistency over aggressive host-damaging properties. Some bacterial properties suggest an alliance with the host to keep transient, potential pathogens at bay, such as the ability of S. epidermidis to produce antimicrobials, or the production of short-chain fatty acids by P. acnes. These features can function together with host-derived components of the innate host defence to establish and maintain the composition of a health-associated skin microbiota. However, depending largely on the host status, the relationship between the human host and S. epidermidis/P. acnes can also have parasitic features. Both microorganisms are frequently isolated from opportunistic infections. S. epidermidis is a causative agent of hospital-acquired infections, mostly associated with the use of medical devices. P. acnes is suspected to be of major importance in the pathogenesis of acne and also in a number of other opportunistic infections. In this review we will present bacterial factors and traits of these two key members of our skin microbiota and discuss how they contribute to mutualistic and parasitic properties. The elucidation of their roles in health-promoting or disease-causing processes could lead to new prophylactic and therapeutic strategies against skin disorders and other S. epidermidis/P. acnes-associated diseases, and increase our understanding of the delicate interplay of the skin microbiota with the human host.

Accumulation-associated protein enhances Staphylococcus epidermidis biofilm formation under dynamic conditions and is required for infection in a rat catheter model

Biofilm formation is the primary virulence factor of Staphylococcus epidermidis. S. epidermidis biofilms preferentially form on abiotic surfaces and may contain multiple matrix components, including proteins such as accumulation-associated protein (Aap). Following proteolytic cleavage of the A domain, which has been shown to enhance binding to host cells, B domain homotypic interactions support cell accumulation and biofilm formation. To further define the contribution of Aap to biofilm formation and infection, we constructed an aap allelic replacement mutant and an icaADBC aap double mutant. When subjected to fluid shear, strains deficient in Aap production produced significantly less biofilm than Aap-positive strains. To examine the in vivo relevance of our findings, we modified our previously described rat jugular catheter model and validated the importance of immunosuppression and the presence of a foreign body to the establishment of infection. The use of our allelic replacement mutants in the model revealed a significant decrease in bacterial recovery from the catheter and the blood in the absence of Aap, regardless of the production of polysaccharide intercellular adhesin (PIA), a well-characterized, robust matrix molecule. Complementation of the aap mutant with full-length Aap (containing the A domain), but not the B domain alone, increased initial attachment to microtiter plates, as did in trans expression of the A domain in adhesion-deficient Staphylococcus carnosus. These results demonstrate Aap contributes to S. epidermidis infection, which may in part be due to A domain-mediated attachment to abiotic surfaces.

Coagulase-negative staphylococci

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

Foreign Body Infection Models to Study Host-Pathogen Response and Antimicrobial Tolerance of Bacterial Biofilm

The number of implanted medical devices is steadily increasing and has become an effective intervention improving life quality, but still carries the risk of infection. These infections are mainly caused by biofilm-forming staphylococci that are difficult to treat due to the decreased susceptibility to both antibiotics and host defense mechanisms. To understand the particular pathogenesis and treatment tolerance of implant-associated infection (IAI) animal models that closely resemble human disease are needed. Applications of the tissue cage and catheter abscess foreign body infection models in the mouse will be discussed herein. Both models allow the investigation of biofilm and virulence of various bacterial species and a comprehensive insight into the host response at the same time. They have also been proven to serve as very suitable tools to study the anti-adhesive and anti-infective efficacy of different biomaterial coatings. The tissue cage model can additionally be used to determine pharmacokinetics, efficacy and cytotoxicity of antimicrobial compounds as the tissue cage fluid can be aspirated repeatedly without the need to sacrifice the animal. Moreover, with the advance in innovative imaging systems in rodents, these models may offer new diagnostic measures of infection. In summary, animal foreign body infection models are important tools in the development of new antimicrobials against IAI and can help to elucidate the complex interactions between bacteria, the host immune system, and prosthetic materials.

Antibodies to PhnD inhibit staphylococcal biofilms

Biofilm formation on central lines or peripheral catheters is a serious threat to patient well-being. Contaminated vascular devices can act as a nidus for bloodstream infection and systemic pathogen dissemination. Staphylococcal biofilms are the most common cause of central-line-associated bloodstream infections, and antibiotic resistance makes them difficult to treat. As an alternative to antibiotic intervention, we sought to identify anti-staphylococcal biofilm targets for the development of a vaccine or antibody prophylactic. A screening strategy was devised using a microfluidic system to test antibody-mediated biofilm inhibition under biologically relevant conditions of shear flow. Affinity-purified polyclonal antibodies to target antigen PhnD inhibited both Staphylococcus epidermidis and S. aureus biofilms. PhnD-specific antibodies blocked biofilm development at the initial attachment and aggregation stages, and deletion of phnD inhibited normal biofilm formation. We further adapted our microfluidic biofilm system to monitor the interaction of human neutrophils with staphylococcal biofilms and demonstrated that PhnD-specific antibodies also serve as opsonins to enhance neutrophil binding, motility, and biofilm engulfment. These data support the identification of PhnD as a lead target for biofilm intervention strategies performed either by vaccination or through passive administration of antibodies.