Factors characterizing Staphylococcus epidermidis invasiveness determined by comparative genomics

Isolation and identification of metallotolerant bacteria with a potential biotechnological application

Mining has led to severe environmental pollution in countries with exhaustive mining production and inadequate industrial waste regulation. Microorganisms in contaminated sites, like mine tailings, have adapted to high concentrations of heavy metals, developing the capacity of reducing or removing them from these environments. Therefore, it is essential to thoroughly characterize bacteria present in these sites to find different ways of bioremediation. In this regard, in this study, an enrichment and isolation procedure were performed to isolate bacteria with lower nutritional requirements and high tolerance to Cu(II) and Fe(II) from two Sonoran River basin mining tails. Two Staphylococcus species and a Microbacterium ginsengisoli strain were isolated and identified from the San Felipe de Jesús mining tail. Also, three strains were isolated from the Nacozari de García mining tail: Burkholderia cenocepacia, Sphingomonas sp. and Staphylococcus warneri. Significant microbiological differences were found between the two sites. All these species exhibited tolerance up to 300 mg/L for Cu (II)-Fe (II) solutions, indicating their capacity to grow in these conditions. Moreover, a consortium of isolated bacteria was immobilized in two different biocomposites and the biocomposite with larger pore size achieved greater bacterial immobilization showcasing the potential of these bacteria in biotechnological applications.

Improved Genomic Prediction of Staphylococcus epidermidis Isolation Sources with a Novel Polygenic Score

Staphylococcus epidermidis infections can be challenging to diagnose due to the species frequent contamination of clinical specimens and indolent course of infection. Nevertheless, S. epidermidis is the major cause of late-onset sepsis among premature infants and of intravascular infection in all age groups. Prior work has shown that bacterial virulence factors, antimicrobial resistances, and strains have up to 80% in-sample accuracy to distinguish hospital from community sources, but are unable to distinguish true bacteremia from blood culture contamination. Here, a phylogeny-informed genome-wide association study of 88 isolates was used to estimate effect sizes of particular genomic variants for isolation sources. A "polygenic score" was calculated for each isolate as the summed effect sizes of its repertoire of genomic variants. Predictive models of isolation sources based on polygenic scores were tested with in-samples and out-samples from prior studies of different patient populations. Polygenic scores from accessory genes (AGs) distinguished hospital from community sources with the highest accuracy to date, up to 98% for in-samples and 65% to 91% for various out-samples, whereas scores from single nucleotide polymorphisms (SNPs) had lower accuracy. Scores from AGs and SNPs achieved the highest in-sample accuracy to date, up to 76%, in distinguishing infection from contaminant sources within a hospital. Model training and testing data sets with more similar population structures resulted in more accurate predictions. This study reports the first use of a polygenic score for predicting a complex bacterial phenotype and shows the potential of this approach for enhancing S. epidermidis diagnosis.

Adhesive Virulence Factors of Staphylococcus aureus Resist Digestion by Coagulation Proteases Thrombin and Plasmin

Staphylococcus aureus (S. aureus) is an invasive and life-threatening pathogen that has undergone extensive coevolution with its mammalian hosts. Its molecular adaptations include elaborate mechanisms for immune escape and hijacking of the coagulation and fibrinolytic pathways. These capabilities are enacted by virulence factors including microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) and the plasminogen-activating enzyme staphylokinase (SAK). Despite the ability of S. aureus to modulate coagulation, until now the sensitivity of S. aureus virulence factors to digestion by proteases of the coagulation system was unknown. Here, we used protein engineering, biophysical assays, and mass spectrometry to study the susceptibility of S. aureus MSCRAMMs to proteolytic digestion by human thrombin, plasmin, and plasmin/SAK complexes. We found that MSCRAMMs were highly resistant to proteolysis, and that SAK binding to plasmin enhanced this resistance. We mapped thrombin, plasmin, and plasmin/SAK cleavage sites of nine MSCRAMMs and performed biophysical, bioinformatic, and stability analysis to understand structural and sequence features common to protease-susceptible sites. Overall, our study offers comprehensive digestion patterns of S. aureus MSCRAMMs by thrombin, plasmin, and plasmin/SAK complexes and paves the way for new studies into this resistance and virulence mechanism.

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.

Two novel aliphatic unsaturated alcohols isolated from a pathogenic fungus Fusarium proliferatum

Phytopathogenic fungi have attracted great attention as a promising source for new drug discovery. In the progress of our ongoing study for bioactive natural products from an in-house phytopathogenic fungi library, a pathogenic fungus, Fusarium proliferatum strain 13294 (FP13294), was selected for chemical investigation. Two novel aliphatic unsaturated alcohols named fusariumnols A and B (1 and 2), together with one previously characterized sesquiterpenoid lignoren (3) were identified. Structures of 1-3 were assigned by mass spectrometry and NMR spectroscopy. Their bioactivities were assessed against Staphylococcus epidermidis, S. aureus, and Methicillin-resistant S. aureus (MRSA). Compounds 1 and 2 exhibited weak antibacterial activity against S. epidermidis (MIC = 100 μM).

Phenotypic profile and antibiogram of biofilm-producing bacteria isolates from diabetic foot ulcers in Zaria, Nigeria

Background

Diabetic foot ulcers (DFUs) present with high morbidity and reduce patient's quality of life. There is a gross paucity of data on biofilm-producing bacteria in DFU Infection in North-Western Nigeria. The study sought to determine the biofilm-forming ability of bacteria isolates from DFUs and determine their antimicrobial susceptibility pattern in Zaria, North-Western Nigeria.

Materials and Methods

This hospital-based cross-sectional study of patients with DFUs was conducted from June 2018 to February 2020. Consecutive biopsies were aseptically collected. Bacteria were isolated and identified using a Microgen kit. Biofilm forming ability and antibiogram of isolates were determined using microtitre plate and disk diffusion methods, respectively.

Results

Of the 225 participants enrolled, males constituted the majority, 144 (64.0%) with 88 (36.0%) females, the median age of participants was 54 (48-60) years, and the age range was 36-77 years. A total of 172 bacteria were isolated, and 123 (71.5%) were biofilm producers. Staphylococcus aureus (26.7%) was the highest biofilm producer, while Citrobacter freundii and Stenotrophomonas maltophilia were the least biofilm producers, 1 (0.6%) each. A disproportionate resistance pattern was demonstrated among the biofilm and non-biofilm producers against the cephalosporins tested, ceftazidime (68% vs. 18%), ceftriaxone (50% vs. 8.0%) and cefotaxime (21% vs. 0.0%). About 46% and 68% of the biofilm producers were resistant to gentamycin and ciprofloxacin, respectively. While only 2% of the non-biofilm producers were resistant to imipenem, 11% of the biofilm producers were resistant to it.

Conclusion

These findings revealed a high proportion of biofilm-producing bacteria and were more resistant than non-biofilm producers.

Genomic investigation of clinically significant coagulase-negative staphylococci

Introduction. Coagulase-negative staphylococci have been recognized both as emerging pathogens and contaminants of clinical samples. High-resolution genomic investigation may provide insights into their clinical significance.Aims. To review the literature regarding coagulase-negative staphylococcal infection and the utility of genomic methods to aid diagnosis and management, and to identify promising areas for future research.Methodology. We searched Google Scholar with the terms (Staphylococcus) AND (sequencing OR (infection)). We prioritized papers that addressed coagulase-negative staphylococci, genomic analysis, or infection.Results. A number of studies have investigated specimen-related, phenotypic and genetic factors associated with colonization, infection and virulence, but diagnosis remains problematic.Conclusion. Genomic investigation provides insights into the genetic diversity and natural history of colonization and infection. Such information allows the development of new methodologies to identify and compare relatedness and predict antimicrobial resistance. Future clinical studies that employ suitable sampling frames coupled with the application of high-resolution whole-genome sequencing may aid the development of more discriminatory diagnostic approaches to coagulase-staphylococcal infection.

Bacterial diversity and inflammatory response at first-time visit in younger and older individuals with diabetic foot infection (DFI)

AIM

Infection of a diabetic foot ulcer (DFU) is common. More than the half of DFUs become infected and 15-20% of them necessitate amputation in course of treatment. Diabetic foot infection (DFI) is therefore the major cause for non-traumatic lower limb amputation in Germany. Prompt and effective treatment of DFI is mandatory to safe limbs and lives. We investigated if there are relevant differences in evoked inflammatory response between different species and age-separated groups. We further investigated if there is an impact of ulcer localization on bacterial diversity.

METHODS

For a 12-month period, we investigated 353 individuals with infected DFU, their laboratory results and bacterial diversity at first-time visit in a Diabetic Foot Care Center in Southern Germany.

RESULTS

The ulcer microbiota was dominated by gram-positive species, primary Staphylococcus aureus. The gram-negative sector was mainly formed by Pseudomonas aeruginosa and Enterobacteriaceae (Proteus spp., Enterobacter spp., Escherichia coli and Klebsiella spp.). With increase in age, P. aeruginosa and S. aureus became more frequent, while Streptococci decreased. Ischemic and/or deep wounds were more likely to bear gram-negative species. Inflammatory response did not differ between gram-positive and gram-negative species, while Streptococci and Proteus spp. induced the highest serum inflammation reaction in their category. Streptococci, Enterobacter spp. and E. coli were more frequent in summer, while Enterococci spp., coagulase-negative Staphylococci and P. aeruginosa were more prevalent in winter half-year. DFIs of the forefoot and plantar side are mostly caused by gram-positive species, while Enterobacteriaceae were most frequent in plantar ulcerations.

CONCLUSION

Gram-positive species dominate bacterial spectrum in DFI. With increase in age, S. aureus, Streptococci and Pseudomonas aeruginosa became more frequent. The inflammatory response did not differ significantly between different species, but gram-negative species were slightly but not significant more frequent in ischemic wounds. Climatic distinction like summer or winter half-year as well as foot ulcer localization seems to influence bacterial diversity in DFUs.

Staphylococcal Vaccine Antigens related to biofilm formation

The number and frequency of multidrug-resistant (MDR) strains as a frequent cause of nosocomial infections have increased, especially for Methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis, in part due to device-related infections. The transition to antibiotic-resistance in related bacterial genes and the capability for immune escape have increased the sustainability of biofilms produced by these bacteria. The formation and changes in biofilms have been suggested as a target to prevent or treat staphylococcal infections. Thus, this study reviews the development of candidate staphylococcal vaccines by database searching, and evaluates the immunogenicity and efficacy profiles of bacterial components involved in biofilms. The literature suggests that using common staphylococcal vaccine antigens and multivalent vaccines should further enhance vaccine efficacy.

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.

Comparative Genome Analysis Reveals the Molecular Basis of Niche Adaptation of Staphylococcus epidermidis Strains

Staphylococcus epidermidis is one of the most commonly isolated species from human skin and the second leading cause of bloodstream infections. Here, we performed a large-scale comparative study without any pre-assigned reference to identify genomic determinants associated with the diversity and adaptation of S. epidermidis strains to various environments. Pan-genome of S. epidermidis was open with 435 core proteins and had a pan-genome size of 8,034 proteins. Genome-wide phylogenetic tree showed high heterogeneity and suggested that routine whole genome sequencing was a powerful tool for analyzing the complex evolution of S. epidermidis and for investigating the infection sources. Comparative genome analyses demonstrated a range of antimicrobial resistance (AMR) genes, especially those within mobile genetic elements. The complicated host-bacterium and bacterium-bacterium relationships help S. epidermidis to play a vital role in balancing the epithelial microflora. The highly variable and dynamic nature of the S. epidermidis genome may contribute to its success in adapting to broad habitats. Genes related to biofilm formation and cell toxicity were significantly enriched in the blood and skin, demonstrating their potentials in identifying risk genotypes. This study gave a general landscape of S. epidermidis pan-genome and provided valuable insights into mechanisms for genome evolution and lifestyle adaptation of this ecologically flexible species.

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.

Phenotypic Modulation of Biofilm Formation in a Staphylococcus epidermidis Orthopedic Clinical Isolate Grown Under Different Mechanical Stimuli: Contribution From a Combined Proteomic Study

One of the major causes of prosthetic joint failure is infection. Recently, coagulase negative Staphylococcus epidermidis has been identified as an emergent, nosocomial pathogen involved in subclinical prosthetic joint infections (PJIs). The diagnosis of PJIs mediated by S. epidermidis is usually complex and difficult due to the absence of acute clinical signs derived from the host immune system response. Therefore, analysis of protein patterns in biofilm-producing S. epidermidis allows for the examination of the molecular basis of biofilm formation. Thus, in the present study, the proteome of a clinical isolate S. epidermidis was analyzed when cultured in its planktonic or sessile form to examine protein expression changes depending on culture conditions. After 24 h of culture, sessile bacteria exhibited increased gene expression for ribosomal activity and for production of proteins related to the initial attachment phase, involved in the capsular polysaccharide/adhesin, surface associated proteins and peptidoglycan biosynthesis. Likewise, planktonic S. epidermidis was able to aggregate after 24 h, synthesizing the accumulation associate protein and cell-wall molecules through the activation of the YycFG and ArlRS, two component regulatory pathways. Prolonged culture under vigorous agitation generated a stressful growing environment triggering aggregation in a biofilm-like matrix as a mechanism to survive harsh conditions. Further studies will be essential to support these findings in order to further delineate the complex mechanisms of biofilm formation of S. epidermidis and they could provide the groundwork for the development of new drugs against biofilm-related infections, as well as the identification of novel biomarkers of subclinical or chronic infections mediated by these emerging, low virulence pathogens.

Bacterial Diversity of Diabetic Foot Ulcers: Current Status and Future Prospectives

Diabetic foot ulcers (DFUs) and diabetic foot infections (DFIs) are associated with reduced patient quality of life, lower-extremity amputation, hospitalization, and high morbidity and mortality. Diverse bacterial communities have been identified in DFUs/DFIs, playing a significant role in infection prognosis. However, due to the high heterogeneity of bacterial communities colonized in DFUs/DFIs, culture-based methods may not isolate all of the bacterial population or unexpected microorganisms. Recently, high sensitivity and specificity of DNA (metagenomics) and RNA (metatranscriptomics) technologies have addressed limitations of culture-based methods and have taken a step beyond bacterial identification. As a consequence, new advances obtained from DNA- and RNA-based techniques for bacterial identification can improve therapeutic approaches. This review evaluated the current state of play in aetiology of DFUs/DFIs on culture and molecular approaches, and discussed the impact of metagenomic and metatranscriptomic methods in bacterial identification approaches.

Comparative Genomic Analysis of Staphylococcus haemolyticus Reveals Key to Hospital Adaptation and Pathogenicity

Staphylococcus haemolyticus is a skin commensal gaining increased attention as an emerging pathogen of nosocomial infections. However, knowledge about the transition from a commensal to an invasive lifestyle remains sparse and there is a paucity of studies comparing pathogenicity traits between commensal and clinical isolates. In this study, we used a pan-genomic approach to identify factors important for infection and hospital adaptation by exploring the genomic variability of 123 clinical isolates and 46 commensal S. haemolyticus isolates. Phylogenetic reconstruction grouped the 169 isolates into six clades with a distinct distribution of clinical and commensal isolates in the different clades. Phenotypically, multi-drug antibiotic resistance was detected in 108/123 (88%) of the clinical isolates and 5/46 (11%) of the commensal isolates (p < 0.05). In the clinical isolates, we commonly identified a homolog of the serine-rich repeat glycoproteins sraP. Additionally, three novel capsular polysaccharide operons were detected, with a potential role in S. haemolyticus virulence. Clinical S. haemolyticus isolates showed specific signatures associated with successful hospital adaption. Biofilm forming S. haemolyticus isolates that are resistant to oxacillin (mecA) and aminoglycosides (aacA-aphD) are most likely invasive isolates whereas absence of these traits strongly indicates a commensal isolate. We conclude that our data show a clear segregation of isolates of commensal origin, and specific genetic signatures distinguishing the clinical isolates from the commensal isolates. The widespread use of antimicrobial agents has probably promoted the development of successful hospital adapted clones of S. haemolyticus clones through acquisition of mobile genetic elements or beneficial point mutations and rearrangements in surface associated genes.

Pattern and microbiological characteristics of diabetic foot ulcers in a Nigerian tertiary hospital

Purpose

To determine the pattern and bacteriological characteristics of diabetic foot ulcers in patients attending a tertiary health care facility.

Method

160 Patients with Diabetes Mellitus foot syndrome were recruited, out of which 52 had diabetic foot ulcers. Relevant clinical, biochemical, and microbiological evaluations were carried out on the subjects. Data analysis was done using SPSS version 20. p value was set at <0.05.

Results

52 (32.5%) out of 160 subjects with Diabetes Mellitus Foot Syndrome (DMFS) had diabetic foot ulcers. Poor glycaemic control (mean HbA1c = 9.2 (2.7) %), and abuse of antibiotics (76.9%) characterized the subjects. Foot ulcers mainly involved the right lower limb and followed spontaneous blister formation (50%). Microbiological culture pattern was polymicrobial (71.2%); predominantly anaerobic organisms (53.3%). Gram positive and negative aerobic isolates yielded high sensitivity to common quinolones (76% – 87.8%). The gram positive and negative anaerobic isolates were highly sensitive to Clindamycin and Metronidazole respectively (80.2% – 97.8%). High sensitivity (>80%) yield for gram negative anaerobes was recorded for Imipinem and Ampicillin/Sulbactam.

Conclusion

Diabetic foot ulcers (DFU) contribute about one-third of DMFS. The bacteriological isolates from these ulcers are mainly polymicrobial with high sensitivity to common antibiotics. The need for appropriate use of antibiotics should be advocated among the patients.

Disease-associated genotypes of the commensal skin bacterium Staphylococcus epidermidis

Some of the most common infectious diseases are caused by bacteria that naturally colonise humans asymptomatically. Combating these opportunistic pathogens requires an understanding of the traits that differentiate infecting strains from harmless relatives. Staphylococcus epidermidis is carried asymptomatically on the skin and mucous membranes of virtually all humans but is a major cause of nosocomial infection associated with invasive procedures. Here we address the underlying evolutionary mechanisms of opportunistic pathogenicity by combining pangenome-wide association studies and laboratory microbiology to compare S. epidermidis from bloodstream and wound infections and asymptomatic carriage. We identify 61 genes containing infection-associated genetic elements (k-mers) that correlate with in vitro variation in known pathogenicity traits (biofilm formation, cell toxicity, interleukin-8 production, methicillin resistance). Horizontal gene transfer spreads these elements, allowing divergent clones to cause infection. Finally, Random Forest model prediction of disease status (carriage vs. infection) identifies pathogenicity elements in 415 S. epidermidis isolates with 80% accuracy, demonstrating the potential for identifying risk genotypes pre-operatively.

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.

Comparative Genomics Study of Staphylococcus epidermidis Isolates from Orthopedic-Device-Related Infections Correlated with Patient Outcome

Staphylococcus epidermidis has emerged as an important opportunistic pathogen causing orthopedic-device-related infections (ODRI). This study investigated the association of genome variation and phenotypic features of the infecting S. epidermidis isolate with the clinical outcome for the infected patient. S. epidermidis isolates were collected from 104 patients with ODRI. Their clinical outcomes were evaluated, after an average of 26 months, as either "cured" or "not cured." The isolates were tested for antibiotic susceptibility and biofilm formation. Whole-genome sequencing was performed on all isolates, and genomic variation was related to features associated with "cured" and "not cured." Strong biofilm formation and aminoglycoside resistance were associated with a "not-cured" outcome (P = 0.031 and P < 0.001, respectively). Based on gene-by-gene analysis, some accessory genes were more prevalent in isolates from the "not-cured" group. These included the biofilm-associated bhp gene, the antiseptic resistance qacA gene, the cassette chromosome recombinase-encoding genes ccrA and ccrB, and the IS256-like transposase gene. This study identifies biofilm formation and antibiotic resistance as associated with poor outcome in S. epidermidis ODRI. Whole-genome sequencing identified specific genes associated with a "not-cured" outcome that should be validated in future studies. (The study has been registered at ClinicalTrials.gov with identifier NCT02640937.).

Bacterial colonization and succession in a newly opened hospital

The microorganisms that inhabit hospitals may influence patient recovery and outcome, although the complexity and diversity of these bacterial communities can confound our ability to focus on potential pathogens in isolation. To develop a community-level understanding of how microorganisms colonize and move through the hospital environment, we characterized the bacterial dynamics among hospital surfaces, patients, and staff over the course of 1 year as a new hospital became operational. The bacteria in patient rooms, particularly on bedrails, consistently resembled the skin microbiota of the patient occupying the room. Bacterial communities on patients and room surfaces became increasingly similar over the course of a patient's stay. Temporal correlations in community structure demonstrated that patients initially acquired room-associated taxa that predated their stay but that their own microbial signatures began to influence the room community structure over time. The α- and β-diversity of patient skin samples were only weakly or nonsignificantly associated with clinical factors such as chemotherapy, antibiotic usage, and surgical recovery, and no factor except for ambulatory status affected microbial similarity between the microbiotas of a patient and their room. Metagenomic analyses revealed that genes conferring antimicrobial resistance were consistently more abundant on room surfaces than on the skin of the patients inhabiting those rooms. In addition, persistent unique genotypes of Staphylococcus and Propionibacterium were identified. Dynamic Bayesian network analysis suggested that hospital staff were more likely to be a source of bacteria on the skin of patients than the reverse but that there were no universal patterns of transmission across patient rooms.

Analysis of early mesothelial cell responses to Staphylococcus epidermidis isolated from patients with peritoneal dialysis-associated peritonitis

The major complication of peritoneal dialysis (PD) is the development of peritonitis, an infection within the abdominal cavity, primarily caused by bacteria. PD peritonitis is associated with significant morbidity, mortality and health care costs. Staphylococcus epidermidis is the most frequently isolated cause of PD-associated peritonitis. Mesothelial cells are integral to the host response to peritonitis, and subsequent clinical outcomes, yet the effects of infection on mesothelial cells are not well characterised. We systematically investigated the early mesothelial cell response to clinical and reference isolates of S. epidermidis using primary mesothelial cells and the mesothelial cell line Met-5A. Using an unbiased whole genome microarray, followed by a targeted panel of genes known to be involved in the human antibacterial response, we identified 38 differentially regulated genes (adj. p-value < 0.05) representing 35 canonical pathways after 1 hour exposure to S. epidermidis. The top 3 canonical pathways were TNFR2 signaling, IL-17A signaling, and TNFR1 signaling (adj. p-values of 0.0012, 0.0012 and 0.0019, respectively). Subsequent qPCR validation confirmed significant differences in gene expression in a number of genes not previously described in mesothelial cell responses to infection, with heterogeneity observed between clinical isolates of S. epidermidis, and between Met-5A and primary mesothelial cells. Heterogeneity between different S. epidermidis isolates suggests that specific virulence factors may play critical roles in influencing outcomes from peritonitis. This study provides new insights into early mesothelial cell responses to infection with S. epidermidis, and confirms the importance of validating findings in primary mesothelial cells.

Specific Anti-Leukemic Activity of the Peptide Warnericin RK and Analogues and Visualization of Their Effect on Cancer Cells by Chemical Raman Imaging

Antimicrobial peptides can be used as therapeutic agents against cancer cells. Warnericin RK and derivatives (WarnG20D and WarnF14V) were tested on various, solid tumor or leukemia, cancer cells. These peptides appeared to be cytotoxic on all the cell types tested, cancerous as well healthy, but very interestingly displayed no deleterious effect on healthy mononuclear cells. The mode of action of the peptide was proposed to be membranolytic, using chemical Raman imaging. Addition of peptide induced a large disorganization of the membrane leading to the loss of the content of inner compartments of Jurkat cell, whereas no effect was observed on the healthy mononuclear cells. The less hemolytic peptides WarnG20D and WarnF14V could be good candidates for the leukemia treatment.

Two-component signal transduction system SaeRS is involved in competence and penicillin susceptibility in Staphylococcus epidermidis

Staphylococcus epidermidis, which is a causative pathogen of nosocomial infection, expresses its virulent traits such as biofilm and autolysis regulated by two-component signal transduction system SaeRS. In this study, the S. epidermidis SaeRS was identified to negatively regulate the expression of genes involved in competence (comF, murF), cytolysis (lrgA), and autolysis (lytS) by DNA microarray or real-time RT-PCR analysis. In addition, saeRS mutant showed increased competence and higher susceptibility to antibiotics such as penicillin and oxacillin than the wild-type strain. The study will be helpful for understanding the characterization of the SaeRS in S. epidermidis.

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.

Physical stress and bacterial colonization

Bacterial surface colonizers are subject to a variety of physical stresses. During the colonization of human epithelia such as on the skin or the intestinal mucosa, bacteria mainly have to withstand the mechanical stress of being removed by fluid flow, scraping, or epithelial turnover. To that end, they express a series of molecules to establish firm attachment to the epithelial surface, such as fibrillar protrusions (pili) and surface-anchored proteins that bind to human matrix proteins. In addition, some bacteria--in particular gut and urinary tract pathogens--use internalization by epithelial cells and other methods such as directed inhibition of epithelial turnover to ascertain continued association with the epithelial layer. Furthermore, many bacteria produce multilayered agglomerations called biofilms with a sticky extracellular matrix, providing additional protection from removal. This review will give an overview over the mechanisms human bacterial colonizers have to withstand physical stresses with a focus on bacterial adhesion.

Arginine deiminase in Staphylococcus epidermidis functions to augment biofilm maturation through pH homeostasis

Allelic replacement mutants were constructed within arginine deiminase (arcA1 and arcA2) to assess the function of the arginine deiminase (ADI) pathway in organic acid resistance and biofilm formation of Staphylococcus epidermidis 1457. A growth-dependent acidification assay (pH ∼5.0 to ∼5.2) determined that strain 1457 devoid of arginine deiminase activity (1457 ΔADI) was significantly less viable than the wild type following depletion of glucose and in the presence of arginine. However, no difference in viability was noted for individual 1457 ΔarcA1 (native) or ΔarcA2 (arginine catabolic mobile element [ACME]-derived) mutants, suggesting that the native and ACME-derived ADIs are compensatory in S. epidermidis. Furthermore, flow cytometry and electron paramagnetic resonance spectroscopy results suggested that organic acid stress resulted in oxidative stress that could be partially rescued by the iron chelator dipyridyl. Collectively, these results suggest that formation of hydroxyl radicals is partially responsible for cell death via organic acid stress and that ADI-derived ammonia functions to counteract this acid stress. Finally, static biofilm assays determined that viability, ammonia synthesis, and pH were reduced in strain 1457 ΔADI following 120 h of growth in comparison to strain 1457 and the arcA1 and arcA2 single mutants. It is hypothesized that ammonia synthesis via the ADI pathway is important to reduce pH stress in specific microniches that contain high concentrations of organic acids.

Influence of nanohydroxyapatite surface properties on Staphylococcus epidermidis biofilm formation

Nanohydroxyapatite (nanoHA), due to its chemical properties, has appeared as an exceptionally promising bioceramic to be used as bone regeneration material. Staphylococcus epidermidis have emerged as major nosocomial pathogens associated with infections of implanted medical devices. In this work, the purpose was to study the influence of the nanoHA surface characteristics on S. epidermidis RP62A biofilm formation. Therefore, two different initial inoculum concentrations (Ci) were used in order to check if these would affect the biofilm formed on the nanoHA surfaces. Biofilm formation was followed by the enumeration of cultivable cells and by scanning electron microscopy. Surface topography, contact angle, total surface area and porosimetry of the biomaterials were studied and correlated with the biofilm data. The surface of nanoHA sintered at 830℃ (nanoHA830) showed to be more resistant to S. epidermidis attachment and accumulation than that of nanoHA sintered at 1000℃ (nanoHA1000). The biofilm formed on nanoHA830 presented differences in terms of structure, surface coverage and EPS production when compared to the one formed on nanoHA1000 surface. It was observed that topography and surface area of nanoHA surfaces had influence on the bacterial attachment and accumulation. Ci influenced bacteria attachment and accumulation on nanoHA surfaces over time. The choice of the initial inoculum concentration was relevant proving to have an effect on the extent of adherence thus being a critical point for human health if these materials are used in implantable devices. This study showed that the initial inoculum concentration and surface material properties determine the rate of microbial attachment to substrata and consequently are related to biofilm-associated infections in biomaterials.

R-thanatin inhibits growth and biofilm formation of methicillin-resistant Staphylococcus epidermidis in vivo and in vitro

Staphylococcus epidermidis is one of the most frequent causes of device-associated infections, because it is known to cause biofilms that grow on catheters or other surgical implants. The persistent increasing resistance of S. epidermidis and other coagulase-negative staphylococci (CoNS) has driven the need for newer antibacterial agents with innovative therapeutic strategies. Thanatin is reported to display potent antibiotic activities, especially against extended-spectrum-beta-lactamase-producing Escherichia coli. The present study aimed to investigate whether a shorter derivative peptide (R-thanatin) could be used as a novel antibacterial agent. We found that R-thanatin was highly potent in vitro against coagulase-negative staphylococci, such as S. epidermidis, S. haemolyticus, and S. hominis, and inhibited biofilm formation at subinhibitory concentrations. Properties of little toxicity to human red blood cells (hRBCs) and human umbilical vein endothelial cells, a low incidence of resistance, and relatively high stability in plasma were confirmed. Excellent in vivo protective effects were also observed using a methicillin-resistant S. epidermidis (MRSE)-induced urinary tract infection rat model. Electron microscopy and confocal laser-scanning microscopy analyses suggested that R-thanatin disturbed cell division of MRSE severely, which might be the reason for inhibition of MRSE growth. These findings indicate that R-thanatin is active against the growth and biofilm formation of MRSE in vitro and in vivo. R-thanatin might be considered as a specific drug candidate for treating CoNS infections.

Differing lifestyles of Staphylococcus epidermidis as revealed through Bayesian clustering of multilocus sequence types

Staphylococcus epidermidis is part of the normal bacterial flora of human skin and a leading cause of infections associated with indwelling medical devices. Previous phylogenetic analyses of subgenomic data have been unable to distinguish between S. epidermidis strains with nosocomial or commensal lifestyles, despite the identification of specific phenotypes and accessory genes that may contribute to such lifestyles. To attempt to better define the population structure of this species, the international S. epidermidis multilocus sequence typing database was analyzed with the Bayesian clustering programs STRUCTURE and BAPS. A total of six genetic clusters (GCs) were identified. A local population of S. epidermidis from clinical specimens was classified according to these six GCs, and further characterized for antibiotic susceptibilities, biofilm, and various genetic markers. GC5 was abundant and significantly enriched for isolates that were resistant to four classes of antibiotics, high biofilm production, and positive for the virulence markers icaA, IS256, and sesD/bhp, indicating its potential clinical relevance. In contrast, GC2 was rare and contained the only isolates positive for the putative commensal marker, fdh. GC1 and GC6 were abundant but not significantly associated with any of the examined characteristics, except for sesF/aap and GC6. GC3 was rare and identified as a potential genetic sink that received, but did not donate, core genetic material from other GCs. In conclusion, population genetics analyses were essential for identifying clusters of strains that may differ in their adaptation to nosocomial or commensal lifestyles. These results provide a new, population genetics framework for studying S. epidermidis.

Staphylococcus epidermidis in orthopedic device infections: the role of bacterial internalization in human osteoblasts and biofilm formation

Background

Staphylococcus epidermidis orthopedic device infections are caused by direct inoculation of commensal flora during surgery and remain rare, although S. epidermidis carriage is likely universal. We wondered whether S. epidermidis orthopedic device infection strains might constitute a sub-population of commensal isolates with specific virulence ability. Biofilm formation and invasion of osteoblasts by S. aureus contribute to bone and joint infection recurrence by protecting bacteria from the host-immune system and most antibiotics. We aimed to determine whether S. epidermidis orthopedic device infection isolates could be distinguished from commensal strains by their ability to invade osteoblasts and form biofilms.

Materials and Methods

Orthopedic device infection S. epidermidis strains (n = 15) were compared to nasal carriage isolates (n = 22). Osteoblast invasion was evaluated in an ex vivo infection model using MG63 osteoblastic cells co-cultured for 2 hours with bacteria. Adhesion of S. epidermidis to osteoblasts was explored by a flow cytometric approach, and internalized bacteria were quantified by plating cell lysates after selective killing of extra-cellular bacteria with gentamicin. Early and mature biofilm formations were evaluated by a crystal violet microtitration plate assay and the Biofilm Ring Test method.

Results

No difference was observed between commensal and infective strains in their ability to invade osteoblasts (internalization rate 308+/−631 and 347+/−431 CFU/well, respectively). This low internalization rate correlated with a low ability to adhere to osteoblasts. No difference was observed for biofilm formation between the two groups.

Conclusion

Osteoblast invasion and biofilm formation levels failed to distinguish S. epidermidis orthopedic device infection strains from commensal isolates. This study provides the first assessment of the interaction between S. epidermidis strains isolated from orthopedic device infections and osteoblasts, and suggests that bone cell invasion is not a major pathophysiological mechanism in S. epidermidis orthopedic device infections, contrary to what is observed for S. aureus.

Enriching modern pharmacotherapy through synergy assessment for the combination of natural products and synthetic drugs

5-O-methylglovanon (5-O-MG) is a bioactive compound first isolated and characterized from Glycosmis plants. In this issue, Zhou et al. evaluated the anti-staphylococcal effects of 5-O-MG against ampicillin-resistant isolates of Staphylococcus aureus and S. epidermidis. The authors showed that the combination of 5-O-MG and ampicillin significantly increased the susceptibility of Staphylococcus strains to the drugs by decreasing MICs with a comparable anti-staphylococcal effect to that of β-lactamase inhibitors, suggesting that herbal compounds such as 5-O-MG may be potential candidates for the inhibitor of β-lactamases. This study is another example of synergy assessment of natural products in drug development to likely enrich modern pharmacotherapy.

Comparison of Staphylococcus epidermidis isolated from prosthetic joint infections and commensal isolates in regard to antibiotic susceptibility, agr type, biofilm production, and epidemiology

Staphylococcus epidermidis is the predominant bacterial species in the normal flora of the human skin and superficial mucosal membranes. However, it has also emerged as the most important pathogen in infections related to foreign-body materials, such as prosthetic joints and heart valves. The aims of this study were to characterise S. epidermidis isolated from prosthetic joint infections (PJI; n=61) and commensal isolates from healthy individuals (n=24) in regard to antimicrobial sensitivity, agr type, hld gene presence, biofilm production including presence of ica and aap genes involved in the biofilm formation process and epidemiology using both phenotypic (the PhenePlate-system) and genotypic [multilocus sequence typing (MLST)] methods. Among the PJI isolates, the majority (67%) were multidrug-resistant. Two major clusters of PJI isolates could be identified; 44% belonged to MLST sequence type (ST) 2, all but one were of agr type 1, and 31% were assigned ST215 and were of agr type 3. Of the commensal isolates, only one isolate was multidrug-resistant, and they were more molecular epidemiologically diverse with mainly MLST singletons and a maximum of 3 isolates assigned to the identical ST. Biofilm production was detected in 41% of the PJI isolates and 58% of the commensal isolates, with the aap gene (95%) more frequently detected than the ica genes (62%) in the biofilm-positive isolates. In conclusion, S. epidermidis isolated from PJIs and commensal isolates differed regarding antimicrobial sensitivity and molecular epidemiological typing using MLST, but not substantially in the distribution of agr types, biofilm production, or the presence of ica and aap genes.

Staphylococcus epidermidis pan-genome sequence analysis reveals diversity of skin commensal and hospital infection-associated isolates

BACKGROUND

While Staphylococcus epidermidis is commonly isolated from healthy human skin, it is also the most frequent cause of nosocomial infections on indwelling medical devices. Despite its importance, few genome sequences existed and the most frequent hospital-associated lineage, ST2, had not been fully sequenced.

RESULTS

We cultivated 71 commensal S. epidermidis isolates from 15 skin sites and compared them with 28 nosocomial isolates from venous catheters and blood cultures. We produced 21 commensal and 9 nosocomial draft genomes, and annotated and compared their gene content, phylogenetic relatedness and biochemical functions. The commensal strains had an open pan-genome with 80% core genes and 20% variable genes. The variable genome was characterized by an overabundance of transposable elements, transcription factors and transporters. Biochemical diversity, as assayed by antibiotic resistance and in vitro biofilm formation, demonstrated the varied phenotypic consequences of this genomic diversity. The nosocomial isolates exhibited both large-scale rearrangements and single-nucleotide variation. We showed that S. epidermidis genomes separate into two phylogenetic groups, one consisting only of commensals. The formate dehydrogenase gene, present only in commensals, is a discriminatory marker between the two groups.

CONCLUSIONS

Commensal skin S. epidermidis have an open pan-genome and show considerable diversity between isolates, even when derived from a single individual or body site. For ST2, the most common nosocomial lineage, we detect variation between three independent isolates sequenced. Finally, phylogenetic analyses revealed a previously unrecognized group of S. epidermidis strains characterized by reduced virulence and formate dehydrogenase, which we propose as a clinical molecular marker.

Molecular basis of Staphylococcus epidermidis infections

Staphylococcus epidermidis is the most important member of the coagulase-negative staphylococci and one of the most abundant colonizers of human skin. While for a long time regarded as innocuous, it has been identified as the most frequent cause of device-related infections occurring in the hospital setting and is therefore now recognized as an important opportunistic pathogen. S. epidermidis produces a series of molecules that provide protection from host defenses. Specifically, many proteins and exopolymers, such as the exopolysaccharide PIA, contribute to biofilm formation and inhibit phagocytosis and the activity of human antimicrobial peptides. Furthermore, recent research has identified a family of pro-inflammatory peptides in S. epidermidis, the phenol-soluble modulins (PSMs), which have multiple functions in immune evasion and biofilm development, and may be cytolytic. However, in accordance with the relatively benign relationship that S. epidermidis has with its host, production of aggressive members of the PSM family is kept at a low level. Interestingly, in contrast to S. aureus with its large arsenal of toxins developed for causing infection in the human host, most if not all "virulence factors" of S. epidermidis appear to have original functions in the commensal lifestyle of this bacterium.

In vitro synergistic interaction of 5-O-methylglovanon and ampicillin against ampicillin resistant Staphylococcus aureus and Staphylococcus epidermidis isolates

5-O-methylglovanon (5-O-MG) is a bioactive compound that was first isolated and characterized from Glycosmis plants. In this study, we found that chemically synthesized 5-O-MG has antimicrobial ability against eleven clinical ampicillin resistant Staphylococcus aureus and S. epidermidis isolates. The MICs of 5-O-MG against the S. aureus and S. epidermidis isolates were 12.5-50 μg/mL and 25-50 μg/mL, respectively. In combination with ampicillin, a synergistic interaction between 5-O-MG and ampicillin against the eleven resistant Staphylococcus isolates was observed, with fractional inhibitory concentration indices of 0.03-0125. Moreover, the anti-staphylococcal activity of 5-O-MG in combination with ampicillin was comparable with that of clavulanic acid in combination with ampicillin. The drug combination had no antagonistic effects when tested against any of the strains. Time-killing assays confirmed the synergy between 5-O-MG and ampicillin (p < 0.01). The combination of these two agents yielded greater than a 2 log(10) cfu/mL decrease in comparison with 5-O-MG or ampicillin alone. These findings suggest that 5-O-MG is a promising compound with the potential for future anti-staphylococcal drug development.

Molecular characterization of an early invasive Staphylococcus epidermidis prosthetic joint infection

Historically regarded as a skin commensal, Staphylococcus epidermidis has been increasingly implicated in invasive foreign body infections such as catheter-related bloodstream infections, indwelling device infections, and prosthetic joint infections. We report a case of an aggressive, difficult-to-eradicate, invasive prosthetic hip infection occurring early after hardware implant and associated with a high-grade bacteremia and assess its salient molecular characteristics. The clinical and molecular characteristics of this isolate mirror the pathogenesis and persistence commonly seen with invasive methicillin-resistant S. aureus and may be attributed to the combination of resistance genes (SCCmec type IV), putative virulence factors (arcA and opp3a), cytolytic peptide production (α-type phenol-soluble modulins), and biofilm adhesion, interaction, and maturation (bhp, aap, and β-type phenol-soluble modulins).

Efficacy of intraoperative surgical irrigation with polihexanide and nitrofurazone in reducing bacterial load after nail removal surgery

BACKGROUND

A common challenge of nail avulsion surgery is the associated bacterial contamination and infection that can manifest. The toe has a difficult anatomy to antiseptically prepare and properly maintain throughout the surgical procedure, lending to this widespread problem.

OBJECTIVE

We conducted a controlled, prospective randomized study to examine the antiseptic efficacy of 3 intraoperative irrigation methods during nail avulsion surgery.

METHODS

We compared intraoperative antiseptic irrigation using 0.9% saline solution (24 patients), 0.2% nitrofurazone (22 patients), and 0.1% polihexanide (25 patients). Swab samples were taken from each patient at 5 distinct stages throughout the surgical procedure, and bacterial culture analysis was performed (positive culture rate, total inocula count, reduction of bacterial load, and identification of specific micro-organisms).

RESULTS

All 3 intraoperative irrigation methods reduced the total bacterial load, but polihexanide was significantly more effective. Furthermore, no patient from the polihexanide group developed postoperative infection. The reduction in bacterial load was lost for all 3 methods after partial nail avulsion surgery, returning to similar values as the initial presurgical bacterial load. An intraoperative irrigation step after partial nail avulsion with saline, nitrofurazone, and polihexanide was effective in reducing the bacterial load by 95.2%, 96.6%, and 99.5%, respectively.

LIMITATIONS

Our patients underwent phenol-based nail avulsion, resulting in no bacterial load after complete nail removal because of the intrinsic antiseptic nature of the phenol.

CONCLUSIONS

Intraoperative irrigation with 0.1% polihexanide substantially reduced the bacterial load and subsequent infections, highlighting the importance of an irrigation step in nail avulsion surgery.

Staphylococcus epidermidis device-related infections: pathogenesis and clinical management

Staphylococcus epidermidis, the most frequently isolated coagulase-negative staphylococcus, is the leading cause of infection related to implanted medical devices (IMDs). This is directly related to its capability to establish multilayered, highly structured biofilms on artificial surfaces. At present, conventional systemic therapies using standard antimicrobial agents represent the main strategy to treat and prevent medical device-associated infections. However, device-related infections are notoriously difficult to treat and bacteria within biofilm communities on the surface of IMDs frequently outlive treatment, and removal of the medical device is often required for successful therapy. Importantly, major advances in this research area have been made, leading to a greater understanding of the complexities of biofilm formation of S. epidermidis and resulting in significant developments in the treatment and prevention of infections related to this member of the coagulase-negative group of staphylococci. This review will examine the pathogenesis of the clinically significant S. epidermidis and provide an overview of the conventional and emerging antibiofilm approaches in the management of medical device-associated infections related to this important nosocomial pathogen.

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.

Inhibition of Staphylococcus epidermidis biofilm formation by rabbit polyclonal antibodies against the SesC protein

Several well-studied proteins with defined roles in Staphylococcus epidermidis biofilm formation are LPXTG motif-containing proteins. Here, we investigate the possible use of the LPXTG motif-containing protein SesC (S. epidermidis surface protein C; accession no. NP_765787) as a target for antibodies to prevent biofilm formation. In vitro and in a in vivo rat model of catheter infection, gene and protein expression analysis showed that SesC is expressed more strongly in biofilm-associated cells than in planktonic cells and is expressed particularly during the late phase of in vivo biofilm formation. Polyclonal rabbit antibodies raised against SesC reduced the fibrinogen-binding ability of S. epidermidis RP62A and Staphylococcus aureus RN4220 transformants expressing SesC, inhibited in vitro biofilm formation by S. epidermidis strains 10b and 1457, and significantly reduced the numbers of bacteria in a 1-day-old in vivo biofilm (P < 0.001, one-way analysis of variance). Our findings revealed that SesC is a promising target for prevention and treatment of S. epidermidis biofilms because it affects both the primary attachment and biofilm accumulation phases. The precise role of SesC in biofilm formation remains to be identified.

Staphylococcus epidermidis--the 'accidental' pathogen

Although nosocomial infections by Staphylococcus epidermidis have gained much attention, this skin-colonizing bacterium has apparently evolved not to cause disease, but to maintain the commonly benign relationship with its host. Accordingly, S. epidermidis does not produce aggressive virulence determinants. Rather, factors that normally sustain the commensal lifestyle of S. epidermidis seem to give rise to additional benefits during infection. Furthermore, we are beginning to comprehend the roles of S. epidermidis in balancing the epithelial microflora and serving as a reservoir of resistance genes. In this Review, I discuss the molecular basis of the commensal and infectious lifestyles of S. epidermidis.

Partial atlE sequencing of Staphylococcus epidermidis strains from prosthetic joint infections

Partial atlE sequencing (atlE nucleotides 2782 to 3114 [atlE(2782-3114)]) was performed in 41 Staphylococcus epidermidis isolates from prosthetic joint infections (PJIs) and 44 isolates from skin as controls. The atlE(2782-3114) allele 1 (type strain sequence) was significantly more frequent in PJI strains (38/41 versus 29/44 in controls; P = 0.0023). Most PJI strains were positive for mecA, icaA/icaD, and IS256, and most belonged to the sequence type 27 subgroup, suggesting the involvement of few related clones.

Pathogenomics of the staphylococci: insights into niche adaptation and the emergence of new virulent strains

Because of its importance as a major human and animal pathogen, Staphylococcus aureus has been the focus of intensive research efforts. At the time of writing, the genomes of 14 isolates of S. aureus have been published and released into the public domain with many more genome sequencing projects underway, representing an excellent resource for studies of bacterial evolution and pathogenesis. Recently, whole genome sequences of several other species of the Staphylococcus genus have been completed allowing a comparative genomic analysis of the adaptation of different species to their natural habitats. Here, we summarize selected comparative genomic studies that have contributed to our understanding of how staphylococci adapt to different environments, combat antibiotics and acquire increased virulence.

Foreign body infections due to Staphylococcus epidermidis

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

Endophthalmitis caused by staphylococcus epidermidis: in vitro antibiotic susceptibilities and clinical outcomes

BACKGROUND AND OBJECTIVE

To investigate the antibiotic sensitivities and clinical outcomes of eyes with endophthalmitis caused by methicillin-sensitive versus methicillin-resistant Staphylococcus epidermidis (MSSE/MRSE).

PATIENTS AND METHODS

A retrospective, consecutive case series of all patients with endophthalmitis caused by S. epidermidis from January 1, 1996, through July 1, 2004, was conducted. The antibiotic sensitivities and clinical outcomes were obtained from the corresponding medical records.

RESULTS

The study included 86 eyes of 86 patients with S. epidermidis endophthalmitis (34 MSSE and 52 MRSE). Endophthalmitis categories included cataract surgery (58), glaucoma surgery (12), trauma (7), vitrectomy (4), penetrating keratoplasty (4), and corneal suture ulcer (1). In vitro testing revealed that all MSSE and MRSE isolates were sensitive to vancomycin, 67% of MSSE isolates and 67% of MRSE isolates were sensitive to gatifloxacin, and 73% of MSSE isolates and 67% of MRSE isolates were sensitive to moxifloxacin (overall 68% sensitive). All eyes were treated with intravitreal vancomycin and either ceftazidime or amikacin. Visual acuity improved to a median of 20/80 at 3 months and 20/60 at 1 year. I CONCLUSIONS: In the current study, all MSSE and MRSE isolates were sensitive to vancomycin and 68% were sensitive to the fourth-generation fluoroquinolones. There were no significant differences in visual acuity outcomes of endophthalmitis caused by MSSE versus MRSE isolates.