Correction: Investigation of synovial fluid induced Staphylococcus aureus aggregate development and its impact on surface attachment and biofilm formation.

[This corrects the article DOI: 10.1371/journal.pone.0231791.]

Investigation of <i>Staphylococcus aureus</i> aggregates on orthopedic materials under varying shear stress

Periprosthetic joint infections (PJI) occurring after artificial joint replacement is a major clinical issue requiring multiple surgeries and antibiotic interventions. Staphylococcus aureus is the common bacteria responsible for PJI. Recent in vitro research has shown that staphylococcal strains rapidly form aggregates in the presence of synovial fluid (SF). We hypothesize that these aggregates provide early protection to bacteria entering the wound site allowing the bacteria time to attach to the implant surface leading to biofilm formation. Thus, understanding attachment kinetics of these aggregates is critical in understanding the aggregates adhesion on various biomaterial surfaces. In this study, the number, size and surface area coverage of aggregates as well as of single cells of S. aureus were quantified at various conditions on different orthopedic materials relevant to orthopedic surgery ; Stainless steel (316L), Titanium (Ti), Hydroxyapatite (HA), and Polyethylene (PE). It was observed that, regardless of the material type, SF induced aggregation resulted in reduced aggregate surface attachment and greater aggregate size than the single cell populations under various shear stresses. Additionally, the surface area coverage of bacterial aggregates on PE was relatively high when compared to other materials, which could potentially be due to the rougher surface of PE. Furthermore, increasing shear stress to 78 mPa decreased aggregates attachment on Ti and HA while increasing the aggregates average size. Therefore, this study demonstrates that the SF induced inhibition of aggregates attachment on all materials suggesting that the biofilm formation is initiated by lodging of aggregates on the surface features of implants and host tissues

Investigation of synovial fluid induced Staphylococcus aureus aggregate development and its impact on surface attachment and biofilm formation.

Periprosthetic joint infections (PJIs) are a devastating complication that occurs in 2% of patients following joint replacement. These infections are costly and difficult to treat, often requiring multiple corrective surgeries and prolonged antimicrobial treatments. The Gram-positive bacterium Staphylococcus aureus is one of the most common causes of PJIs, and it is often resistant to a number of commonly used antimicrobials. This tolerance can be partially attributed to the ability of S. aureus to form biofilms. Biofilms associated with the surface of indwelling medical devices have been observed on components removed during chronic infection, however, the development and localization of biofilms during PJIs remains unclear. Prior studies have demonstrated that synovial fluid, in the joint cavity, promotes the development of bacterial aggregates with many biofilm-like properties, including antibiotic resistance. We anticipate these aggregates have an important role in biofilm formation and antibiotic tolerance during PJIs. Therefore, we sought to determine specifically how synovial fluid promotes aggregate formation and the impact of this process on surface attachment. Using flow cytometry and microscopy, we quantified the aggregation of various clinical S. aureus strains following exposure to purified synovial fluid components. We determined that fibrinogen and fibronectin promoted bacterial aggregation, while cell free DNA, serum albumin, and hyaluronic acid had minimal effect. To determine how synovial fluid mediated aggregation affects surface attachment, we utilized microscopy to measure bacterial attachment. Surprisingly, we found that synovial fluid significantly impeded bacterial surface attachment to a variety of materials. We conclude from this study that fibrinogen and fibronectin in synovial fluid have a crucial role in promoting bacterial aggregation and inhibiting surface adhesion during PJI. Collectively, we propose that synovial fluid may have conflicting protective roles for the host by preventing adhesion to surfaces, but by promoting bacterial aggregation is also contributing to the development of antibiotic tolerance

Investigation of synovial fluid induced Staphylococcus aureus aggregate development and its impact on surface attachment and biofilm formation

Periprosthetic joint infections (PJIs) are a devastating complication that occurs in 2% of patients following joint replacement. These infections are costly and difficult to treat, often requiring multiple corrective surgeries and prolonged antimicrobial treatments. The Gram-positive bacterium Staphylococcus aureus is one of the most common causes of PJIs, and it is often resistant to a number of commonly used antimicrobials. This tolerance can be partially attributed to the ability of S. aureus to form biofilms. Biofilms associated with the surface of indwelling medical devices have been observed on components removed during chronic infection, however, the development and localization of biofilms during PJIs remains unclear. Prior studies have demonstrated that synovial fluid, in the joint cavity, promotes the development of bacterial aggregates with many biofilm-like properties, including antibiotic resistance. We anticipate these aggregates have an important role in biofilm formation and antibiotic tolerance during PJIs. Therefore, we sought to determine specifically how synovial fluid promotes aggregate formation and the impact of this process on surface attachment. Using flow cytometry and microscopy, we quantified the aggregation of various clinical S. aureus strains following exposure to purified synovial fluid components. We determined that fibrinogen and fibronectin promoted bacterial aggregation, while cell free DNA, serum albumin, and hyaluronic acid had minimal effect. To determine how synovial fluid mediated aggregation affects surface attachment, we utilized microscopy to measure bacterial attachment. Surprisingly, we found that synovial fluid significantly impeded bacterial surface attachment to a variety of materials. We conclude from this study that fibrinogen and fibronectin in synovial fluid have a crucial role in promoting bacterial aggregation and inhibiting surface adhesion during PJI. Collectively, we propose that synovial fluid may have conflicting protective roles for the host by preventing adhesion to surfaces, but by promoting bacterial aggregation is also contributing to the development of antibiotic tolerance. <br/

Th17 Responses to Collagen Type V, kα1-Tubulin, and Vimentin Are Present Early in Human Development and Persist Throughout Life

T helper 17 (Th17)-dependent autoimmune responses can develop after heart or lung transplantation and are associated with fibro-obliterative forms of chronic rejection; however, the specific self-antigens involved are typically different from those associated with autoimmune disease. To investigate the basis of these responses, we investigated whether removal of regulatory T cells or blockade of function reveals a similar autoantigen bias. We found that Th17 cells specific for collagen type V (Col V), kα1-tubulin, and vimentin were present in healthy adult peripheral blood mononuclear cells, cord blood, and fetal thymus. Using synthetic peptides and recombinant fragments of the Col V triple helical region (α1[V]), we compared Th17 cells from healthy donors with Th17 cells from Col V-reactive heart and lung patients. Although the latter responded well to α1(V) fragments and peptides in an HLA-DR-restricted fashion, Th17 cells from healthy persons responded in an HLA-DR-restricted fashion to fragments but not to peptides. Col V, kα1-tubulin, and vimentin are preferred targets of a highly conserved, hitherto unknown, preexisting Th17 response that is MHC class II restricted. These data suggest that autoimmunity after heart and lung transplantation may result from dysregulation of an intrinsic mechanism controlling airway and vascular homeostasis

Th17 Responses to Collagen Type V, kα1-Tubulin, and Vimentin Are Present Early in Human Development and Persist Throughout Life

T helper 17 (Th17)-dependent autoimmune responses can develop after heart or lung transplantation and are associated with fibro-obliterative forms of chronic rejection; however, the specific self-antigens involved are typically different from those associated with autoimmune disease. To investigate the basis of these responses, we investigated whether removal of regulatory T cells or blockade of function reveals a similar autoantigen bias. We found that Th17 cells specific for collagen type V (Col V), kα1-tubulin, and vimentin were present in healthy adult peripheral blood mononuclear cells, cord blood, and fetal thymus. Using synthetic peptides and recombinant fragments of the Col V triple helical region (α1[V]), we compared Th17 cells from healthy donors with Th17 cells from Col V-reactive heart and lung patients. Although the latter responded well to α1(V) fragments and peptides in an HLA-DR-restricted fashion, Th17 cells from healthy persons responded in an HLA-DR-restricted fashion to fragments but not to peptides. Col V, kα1-tubulin, and vimentin are preferred targets of a highly conserved, hitherto unknown, preexisting Th17 response that is MHC class II restricted. These data suggest that autoimmunity after heart and lung transplantation may result from dysregulation of an intrinsic mechanism controlling airway and vascular homeostasis

<i>Pseudomonas aeruginosa</i> rugose small-colony variants evade host clearance, are hyper-inflammatory, and persist in multiple host environments

<div><p><i>Pseudomonas aeruginosa</i> causes devastating infections in immunocompromised individuals. Once established, <i>P</i>. <i>aeruginosa</i> infections become incredibly difficult to treat due to the development of antibiotic tolerant, aggregated communities known as biofilms. A hyper-biofilm forming clinical variant of <i>P</i>. <i>aeruginosa</i>, known as a rugose small-colony variant (RSCV), is frequently isolated from chronic infections and is correlated with poor clinical outcome. The development of these mutants during infection suggests a selective advantage for this phenotype, but it remains unclear how this phenotype promotes persistence. While prior studies suggest RSCVs could survive by evading the host immune response, our study reveals infection with the RSCV, PAO1Δ<i>wspF</i>, stimulated an extensive inflammatory response that caused significant damage to the surrounding host tissue. In both a chronic wound model and acute pulmonary model of infection, we observed increased bacterial burden, host tissue damage, and a robust neutrophil response during RSCV infection. Given the essential role of neutrophils in <i>P</i>. <i>aeruginosa</i>-mediated disease, we investigated the impact of the RSCV phenotype on neutrophil function. The RSCV phenotype promoted phagocytic evasion and stimulated neutrophil reactive oxygen species (ROS) production. We also demonstrate that bacterial aggregation and TLR-mediated pro-inflammatory cytokine production contribute to the immune response to RSCVs. Additionally, RSCVs exhibited enhanced tolerance to neutrophil-produced antimicrobials including H₂O₂ and the antimicrobial peptide LL-37. Collectively, these data indicate RSCVs elicit a robust but ineffective neutrophil response that causes significant host tissue damage. This study provides new insight on RSCV persistence, and indicates this variant may have a critical role in the recurring tissue damage often associated with chronic infections.</p></div

RSCVs evade neutrophil phagocytosis.

<p>A) Neutrophil phagocytosis was assessed following infection (MOI 1:50) using CLSM. Neutrophils were stained with DAPI (blue), extracellular <i>P</i>. <i>aeruginosa</i> was stained with Alexa Fluor 488 (green), and neutrophil internalized <i>P</i>. <i>aeruginosa</i> was stained with Alexa Fluor 647 (red). White arrows indicate neutrophils containing phagocytosed <i>P</i>. <i>aeruginosa</i>. B) Number of neutrophils containing phagocytosed <i>P. aeruginosa</i> was quantified and the ratio of internalization determined. C) Neutrophil phagocytosis was assessed with or without serum opsonization by quantifying the population containing GFP producing <i>P</i>. <i>aeruginosa</i> following infection (MOI 1:50). Data is presented as mean ± SEM. *p<0.05, **p<0.01.</p

PAO1Δ<i>wspF</i> exhibits tolerance to neutrophil antimicrobial products.

<p>Log phase cultures of PAO1 or PAO1Δ<i>wspF</i> were treated with A) LL-37, B) H₂O₂ and C) HOCl at the labeled concentrations for 15min. CFUs were quantified before and after treatment and log fold killing determined. Data presented as mean ± SEM. ***p<0.001.</p

Bacterial aggregation promotes neutrophil ROS production, but exopolysaccharides alone are not sufficient.

<p>A) ePS was purified from PAO1Δ<i>pel</i>P_BAD-psl, PAO1Δ<i>psl</i>P_BAD-pel, or PAO1Δ<i>pel</i>Δ<i>psl</i> and total carbohydrate was quantified by phenol sulfuric acid assay. PAO1 levels or 10-times PAO1 levels of ePS was added to human neutrophils and the ROS response was measured with a luminol reporter. B) PAO1Δ<i>psl</i>Δ<i>pel</i>/pHERD20T and PAO1Δ<i>psl</i>Δ<i>pel</i>/pCdrAB were grown to log phase in the presence of 1% arabinose leading to the formation of CdrA-mediated aggregates in the strain containing pCdrAB. Primary human neutrophils were infected with bacteria at an MOI (1:50). C) Neutrophils were treated with supernatant collected from cultures of PAO1/pCdrAB or PAO1Δ<i>cdrA</i>/pHERD20T, and ROS was quantified. The AUC of the ROS response over 1h was calculated and normalized by CFUs of the inoculation culture to ensure identical cell numbers regardless of aggregation.</p