Novel animal model for studying the molecular mechanisms of bacterial adhesion to bone-implanted metallic devices: role of fibronectin in Staphylococcus aureus adhesion

Staphylococcus aureus Strain-Dependent Biofilm Formation in Bone-Like Environment

Staphylococcus aureus species is an important threat for hospital healthcare because of frequent colonization of indwelling medical devices such as bone and joint prostheses through biofilm formations, leading to therapeutic failure. Furthermore, bacteria within biofilm are less sensitive to the host immune system responses and to potential antibiotic treatments. We suggested that the periprosthetic bone environment is stressful for bacteria, influencing biofilm development. To provide insights into S. aureus biofilm properties of three strains [including one methicillin-resistant S. aureus (MRSA)] under this specific environment, we assessed several parameters related to bone conditions and expected to affect biofilm characteristics. We reported that the three strains harbored different behaviors in response to the lack of oxygen, casamino acids and glucose starvation, and high concentration of magnesium. Each strain presented different biofilm biomass and live adherent cells proportion, or matrix production and composition. However, the three strains shared common responses in a bone-like environment: a similar production of extracellular DNA and engagement of the SOS response. This study is a step toward a better understanding of periprosthetic joint infections and highlights targets, which could be common among S. aureus strains and for future antibiofilm strategies.

Characterization of an Acute Rodent Osteomyelitis Infectious Model Using a Tibial Intramedullary Implant Inoculation

Chronic osteomyelitis in presence of orthopedic implants is a condition observed in the field of biomaterials as it impairs early bone-implant contact, fixation and integration. In this study, a surgical intramedullary tibial insertion was performed using a titanium wire previously inoculated with Staphylococcus aureus in order to develop an osteomyelitis model in a clinically relevant long bone and in absence of any prophylactic treatment. As such, twenty-two male Sprague-Dawley rats received a sterile or inoculated intramedullary biomaterial with either 2 × 10⁶ or 1 × 10⁷S. aureus colony forming units. Bacterial burden, inflammation, morphological changes, as well as newly formed bone tissues were evaluated for histopathology following a period of either eight or fifteen days of implantation. The implant inoculated in presence of the highest bacterial load was effective to produce significant periprosthetic infection observations in addition to hard and soft tissue inflammation consistent with the development of osteomyelitis. In contrast, neither the sterile nor the low-dose implant inoculation showed inflammation and clinical infection signs, but rather produced an expected bone remodeling and appropriate healing associated with biomaterial implantation. Complete health assessment is presented with histopathological periprosthetic results.

Staphylococcus aureus Aggregates on Orthopedic Materials under Varying Levels of Shear Stress

Periprosthetic joint infection (PJI) occurring after artificial joint replacement is a major clinical issue requiring multiple surgeries and antibiotic interventions. Staphylococcus aureus is the bacterium most commonly 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 them time to attach to the implant surface, leading to biofilm formation. Thus, understanding the attachment kinetics of these aggregates is critical in understanding their adhesion to 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 under 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 compared to that on other materials, which could potentially be due to the rougher surface of PE. Furthermore, increasing shear stress to 78 mPa decreased aggregate attachment to Ti and HA while increasing the aggregates' average size. Therefore, this study demonstrates that SF induced inhibition of aggregate attachment to all materials, suggesting that biofilm formation is initiated by lodging of aggregates on the surface features of implants and host tissues.IMPORTANCE Periprosthetic joint infection occurring after artificial joint replacement is a major clinical issue that require repeated surgeries and antibiotic interventions. Unfortunately, 26% of patients die within 5 years of developing these infections. Staphylococcus aureus is the bacterium most commonly responsible for this problem and can form biofilms to provide protection from antibiotics as well as the immune system. Although biofilms are evident on the infected implants, it is unclear how these are attached to the surface in the first place. Recent in vitro investigations have shown that staphylococcal strains rapidly form aggregates in the presence of synovial fluid and provide protection to bacteria, thus allowing them time to attach to the implant surface, leading to biofilm formation. In this study, we investigated the attachment kinetics of Staphylococcus aureus aggregates on different orthopedic materials. The information presented in this article will be useful in surgical management and implant design.

A comprehensive review of bacterial osteomyelitis with emphasis on Staphylococcus aureus

Osteomyelitis, a significant infection of bone tissue, gives rise to two main groups of infection: acute and chronic. These groups are further categorized in terms of the duration of infection. Usually, children and adults are more susceptible to acute and chronic infections, respectively. The aforementioned groups of osteomyelitis share almost 80% of the corresponding bacterial pathogens. Among all bacteria, Staphylococcus aureus (S. aureus) is a significant pathogen and is associated with a high range of osteomyelitis symptoms. S. aureus has many strategies for interacting with host cells including Small Colony Variant (SCV), biofilm formation, and toxin secretion. In addition, it induces an inflammatory response and causes host cell death by apoptosis and necrosis. However, any possible step to take in this respect is dependent on the conditions and host responses. In the absence of any immune responses and antibiotics, bacteria actively duplicate themselves; however, in the presence of phagocytic cell and harassing conditions, they turn into a SCV, remaining sustainable for a long time. SCV is characterized by notable advantages such as (a) intracellular life that mediates a dam against immune cells and (b) low ATP production that mediates resistance against antibiotics.

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.

Prevention, Diagnosis, and Treatment of Implant Infection in the Distal Upper Extremity

Implant related infection is relatively unusual in surgery to the hand and distal upper limb. When such infections occur, the consequences can be devastating. We review the latest guidance and research on the prevention, diagnosis, and management of implant-associated infections in the hand and distal upper limb.

Testing the efficacy of antimicrobial peptides in the topical treatment of induced osteomyelitis in rats

Joint replacement infections and osteomyelitis are among the most serious complications in orthopaedics and traumatology. The risk factors for these infections are often bacterial resistance to antimicrobials. One of the few solutions available to control bacterial resistance involves antimicrobials, which have a different mechanism of action from traditional antibiotics. Antimicrobial peptides (AMP) appear to be highly promising candidates in the treatment of resistant infections. We have identified several AMP in the venom of various wild bees and designed analogues that show potent antimicrobial activity and low toxicity against eukaryotic cells. The aim of the present study was to test the efficacy of one of those synthetic peptide analogues for the treatment of acute osteomyelitis invoked in laboratory rats. Femoral cavities of 20 laboratory Wistar rats were infected with Staphylococcus aureus. After 1 week, eight rats received an injectable calcium phosphate carrier alone, another eight rats were treated with a calcium phosphate mixed with AMP, and four rats were left without any further treatment. After another week, all rats were euthanized and radiographs were made of both the operated and healthy limbs. The animals with the carrier alone exhibited more severe acute osteomyelitis on radiographs in comparison to the recipients of the calcium phosphate carrier loaded AMP and untreated infected individuals. Based on the results of the above mentioned experiment, it was concluded that when injected directly into the site of femoral acute osteomyelitis, the calcium phosphate carrier mixed with AMP reduced osteomyelitis signs visible on radiographs.

Staphylococcus aureus infections: epidemiology, pathophysiology, clinical manifestations, and management

Staphylococcus aureus is a major human pathogen that causes a wide range of clinical infections. It is a leading cause of bacteremia and infective endocarditis as well as osteoarticular, skin and soft tissue, pleuropulmonary, and device-related infections. This review comprehensively covers the epidemiology, pathophysiology, clinical manifestations, and management of each of these clinical entities. The past 2 decades have witnessed two clear shifts in the epidemiology of S. aureus infections: first, a growing number of health care-associated infections, particularly seen in infective endocarditis and prosthetic device infections, and second, an epidemic of community-associated skin and soft tissue infections driven by strains with certain virulence factors and resistance to β-lactam antibiotics. In reviewing the literature to support management strategies for these clinical manifestations, we also highlight the paucity of high-quality evidence for many key clinical questions.

A systematic review of animal models for Staphylococcus aureus osteomyelitis

Staphylococcus aureus (S. aureus) osteomyelitis is a significant complication for orthopaedic patients undergoing surgery, particularly with fracture fixation and arthroplasty. Given the difficulty in studying S. aureus infections in human subjects, animal models serve an integral role in exploring the pathogenesis of osteomyelitis, and aid in determining the efficacy of prophylactic and therapeutic treatments. Animal models should mimic the clinical scenarios seen in patients as closely as possible to permit the experimental results to be translated to the corresponding clinical care. To help understand existing animal models of S. aureus, we conducted a systematic search of PubMed and Ovid MEDLINE to identify in vivo animal experiments that have investigated the management of S. aureus osteomyelitis in the context of fractures and metallic implants. In this review, experimental studies are categorised by animal species and are further classified by the setting of the infection. Study methods are summarised and the relevant advantages and disadvantages of each species and model are discussed. While no ideal animal model exists, the understanding of a model's strengths and limitations should assist clinicians and researchers to appropriately select an animal model to translate the conclusions to the clinical setting.

Synthesis of lipoteichoic acids in Bacillus anthracis

Lipoteichoic acid (LTA), a glycerol phosphate polymer, is a component of the envelope of Gram-positive bacteria that has hitherto not been identified in Bacillus anthracis, the causative agent of anthrax. LTA synthesis in Staphylococcus aureus and other microbes is catalyzed by the product of the ltaS gene, a membrane protein that polymerizes polyglycerol phosphate from phosphatidyl glycerol. Here we identified four ltaS homologues, designated ltaS1 to -4, in the genome of Bacillus anthracis. Polyglycerol phosphate-specific monoclonal antibodies were used to detect LTA in the envelope of B. anthracis strain Sterne (pXO1(+) pXO2(-)) vegetative forms. B. anthracis mutants lacking ltaS1, ltaS2, ltaS3, or ltaS4 did not display defects in growth or LTA synthesis. In contrast, B. anthracis strains lacking both ltaS1 and ltaS2 were unable to synthesize LTA and exhibited reduced viability, altered envelope morphology, aberrant separation of vegetative forms, and decreased sporulation efficiency. Expression of ltaS1 or ltaS2 alone in B. anthracis as well as in other microbes was sufficient for polyglycerol phosphate synthesis. Thus, similar to S. aureus, B. anthracis employs LtaS enzymes to synthesize LTA, an envelope component that promotes bacterial growth and cell division.

[Treatment of infected breast implant in reconstructive surgery]

OBJECTIVE OF THE STUDY

Immediate failure in breast surgery with implant is a serious medical complication with negative ramifications for both the patient and the health care system. The classical treatment is removal of the breast implant and delay reconstruction. Our objective is to show that this standard treatment is not the good one in many cases, and abundant irrigation with implant salvage is a sure and effective alternative.

PATIENTS AND METHODS

Between January 2001 and December 2009, among the 680 patients who had a breast reconstruction, 18 were operated using the same protocol treatment by the same surgeon: implant removal, irrigation, implant replacement, antibiotic treatment.

RESULTS

After a median month follow-up period of 30 months, definitive conservation of the breast implant was obtained in all of the cases.

CONCLUSION

This preliminary study provides encouraging results in a selected patient population improving the possibility of a conservative treatment according to a precise and rigourous protocol.

Local antibiotic therapy in osteomyelitis

The local delivery of antibiotics in the treatment of osteomyelitis has been used safely and effectively for decades. Multiple methods of drug delivery have been developed for the purposes of both infection treatment and prophylaxis. The mainstay of treatment in this application over the past 20 years has been non-biodegradable polymethylmethacrylate, which has the advantages of excellent elution characteristics and structural support properties. Biodegradable materials such as calcium sulfate and bone graft substitutes have been used more recently for this purpose. Other biodegradable implants, including synthetic polymers, are not yet approved for use but have demonstrated potential in laboratory investigations. Antibiotic-impregnated metal, a recent development, holds great promise in the treatment and prophylaxis of osteomyelitis in the years to come.

Bacterial adherence on UHMWPE with vitamin E: an in vitro study

Orthopaedic materials may improve its capacity to resist bacterial adherence, and subsequent infection. Our aim was to test the bacterial adherence to alpha-tocopherol (frequently named vitamin E, VE) doped or blended UHMWPE with S. aureus and S. epidermidis, compared to virgin material. Collection strains and clinical strains isolated from patients with orthopaedic infections were used, with the biofilm-developing ability as a covariable. While collection strains showed significantly less adherence to VE-UHMWPE, some clinical strains failed to confirm this effect, leading to the conclusion that VE doped or blended UHMWPE affects the adherence of some S. epidermidis and S. aureus strains, independently of the concentration in use, but the results showed important intraspecies differences and cannot be generalized.

Relevant role of fibronectin-binding proteins in Staphylococcus aureus biofilm-associated foreign-body infections

Staphylococcus aureus can establish chronic infections on implanted medical devices due to its capacity to form biofilms. Analysis of the factors that assemble cells into a biofilm has revealed the occurrence of strains that produce either a polysaccharide intercellular adhesin/poly-N-acetylglucosamine (PIA/PNAG) exopolysaccharide- or a protein-dependent biofilm. Examination of the influence of matrix nature on the biofilm capacities of embedded bacteria has remained elusive, because a natural strain that readily converts between a polysaccharide- and a protein-based biofilm has not been studied. Here, we have investigated the clinical methicillin (meticillin)-resistant Staphylococcus aureus strain 132, which is able to alternate between a proteinaceous and an exopolysaccharidic biofilm matrix, depending on environmental conditions. Systematic disruption of each member of the LPXTG surface protein family identified fibronectin-binding proteins (FnBPs) as components of a proteinaceous biofilm formed in Trypticase soy broth-glucose, whereas a PIA/PNAG-dependent biofilm was produced under osmotic stress conditions. The induction of FnBP levels due to a spontaneous agr deficiency present in strain 132 and the activation of a LexA-dependent SOS response or FnBP overexpression from a multicopy plasmid enhanced biofilm development, suggesting a direct relationship between the FnBP levels and the strength of the multicellular phenotype. Scanning electron microscopy revealed that cells growing in the FnBP-mediated biofilm formed highly dense aggregates without any detectable extracellular matrix, whereas cells in a PIA/PNAG-dependent biofilm were embedded in an abundant extracellular material. Finally, studies of the contribution of each type of biofilm matrix to subcutaneous catheter colonization revealed that an FnBP mutant displayed a significantly lower capacity to develop biofilm on implanted catheters than the isogenic PIA/PNAG-deficient mutant.

Reactivation of dormant lumbar methicillin-resistant Staphylococcus aureus osteomyelitis after 12 years

The adequate treatment of methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis has intrigued clinicians for some time. As the resistance of these pathogens, coupled with the increase in community-acquired cases, continues steadily to rise, clinicians are finding it useful to employ multi-modal approaches for efficacious treatment. The authors present a single case report of a patient with recurrent MRSA osteomyelitis, lumbar paraspinal and epidural abscess. He was found to have decreased muscle strength and was hyporeflexic in the involved extremity. Serum testing demonstrated MRSA bacteremia. Neuroimaging studies revealed evidence of paraspinal abscess and a presumed herniated nucleus pulposus at the L5/S1 interspace with significant nerve root compromise. Despite antimicrobials, his symptoms persisted, necessitating surgical exploration. At surgery, paraspinal and epidural abscesses were encountered and debrided; however, no herniated disc was visualized. This case demonstrates the diagnostic and therapeutic dilemmas with which these lesions present. We postulate that the MRSA osteomyelitis/discitis pathogens were walled off in the disc space and subsequently inoculated the soft tissues with ensuing bacteremia. We concur that antimicrobial treatment should be the first line of therapy for these patients; however, surgical debridements and cautious spinal instrumentation should be employed where appropriate.

Tolerance of staphylococci to bactericidal antibiotics

Antibiotic therapy for deep-seated staphylococcal infections, especially when they are associated with artificial devices used for orthopedic surgery is often associated with failure. Standard anti-staphylococcal bactericidal antibiotics, such as semi-synthetic penicillins, cephalosporins, or glycopeptides, are effective when given prophylactically in clinical conditions or experimental trials of implant-related infections. However, the efficacy of all anti-staphylococcal agents is seriously diminished on already established implant-related deep-seated infections, which then frequently require surgical implant removal to obtain a cure. The failure of antibiotic therapy to cure established staphylococcal foreign-body infections may arise in part from a broad-spectrum phenotypic tolerance expressed in vivo to different classes of antimicrobial agents. The molecular and physiological mechanisms of this in vivo tolerance remain poorly understood.

Osteomyelitis and pathological mandibular fracture related to a late implant failure: A clinical report

This clinical report describes an unusual consequence of peri-implantitis and subsequent implant failure in a 72-year-old man. Following uneventful implant removal, osteomyelitis developed at the implant site, which subsequently weakened the mandible sufficiently for a pathological fracture to occur. The patient was treated successfully by use of an intensive oral hygiene regime, antibiotics, and conservative management. The consequences and management of implant failure are discussed, as well as issues relating to the management of osteomyelitis and pathological bone fracture.

Adaptation of Methicillin-Resistant Staphylococcus aureus in the Face of Vancomycin Therapy

For the past 2 decades, vancomycin has served as the cornerstone of therapy against serious methicillin-resistant Staphylococcus aureus infections. This role is increasingly challenged by questions of efficacy, including reduced efficacy against infections caused by glycopeptide-intermediate S. aureus strains. In an evaluation of clinical glycopeptide-intermediate S. aureus isolates and serial, clinical methicillin-resistant S. aureus isolates obtained from patients receiving vancomycin for the treatment of bacteremia, we found that loss of function of the accessory gene regulator operon may confer a survival advantage to S. aureus under vancomycin selection pressure, particularly in strains with the accessory gene regulator group II genotype. Other advantages in a nosocomial setting may include enhancement of biofilm formation and promotion of physiologic changes supporting colonization. We conclude that loss of accessory gene regulator function in methicillin-resistant S. aureus might, in part, explain the decreased efficacy of vancomycin in the therapy of methicillin-resistant S. aureus bacteremia, thus highlighting the need to reevaluate the criteria of susceptibility to vancomycin.

Induction of fibronectin adhesins in quinolone-resistant Staphylococcus aureus by subinhibitory levels of ciprofloxacin or by sigma B transcription factor activity is mediated by two separate pathways

We recently reported on the involvement of a RecA-LexA-dependent pathway in the ciprofloxacin-triggered upregulation of fibronectin-binding proteins (FnBPs) by fluoroquinolone-resistant Staphylococcus aureus. The potential additional contribution of the transcription factor sigma B (SigB) to the ciprofloxacin-triggered upregulation of FnBPs was studied in isogenic mutants of fluoroquinolone-resistant strain RA1 (a topoisomerase IV gyrase double mutant of S. aureus NCTC strain 8325), which exhibited widely different levels of SigB activity, as assessed by quantitative reverse transcription-PCR of their respective sigB and SigB-dependent asp23 transcript levels. These mutants were Tn551 insertion sigB strain TE1 and rsbU(+) complemented strain TE2, which exhibited a wild-type SigB operon. Levels of FnBP surface display and fibronectin-mediated adhesion were lower in sigB mutant TE1 or higher in the rsbU(+)-restored strain TE2 compared to their sigB(+) but rsbU parent, strain RA1, exhibiting low levels of SigB activity. Steady-state fnbA and fnbB transcripts levels were similar in strains TE1 and RA1 but increased by 4- and 12-fold, respectively, in strain TE2 compared to those in strain RA1. In contrast, fibronectin-mediated adhesion of strains TE1, RA1, and TE2 was similarly enhanced by growth in the presence of one-eighth the MIC of ciprofloxacin, which led to a significantly higher increase in their fnbB transcript levels compared to the increase in their fnbA transcript levels. Increased SigB levels led to a significant reduction in agr RNAIII; in contrast, it led to a slight increase in sarA transcript levels. In conclusion, upregulation of FnBPs by increased SigB levels and ciprofloxacin exposure in fluoroquinolone-resistant S. aureus occurs via independent pathways whose concerted actions may significantly promote bacterial adhesion and colonization.

Physiopathologie des infections sur matériel orthopédique

Orthopedic biomaterials are foreign bodies and the molecular architecture of their surfaces provides a point of attachment for bacteria. This adherence is made possible through the interaction of the protein interface and the bacterial adhesins. Bacterial colonies use slime and biofilm as means of protection. The development of bacteria towards a reversible state of stationary growth or microcolony variants permits their survival. Microparticles released by biomaterials cause the chronic inflammation associated with the aseptic loosening of prostheses. Some bacterial sub-populations develop transitory resistance to bactericidal antibiotics in the presence of these materials.

Osteomyelitis in long bones

Osteomyelitis in long bones remains challenging and expensive to treat, despite advances in antibiotics and new operative techniques. Plain radiographs still provide the best screening for acute and chronic osteomyelitis. Other imaging techniques may be used to determine diagnosis and aid in treatment decisions. The decision to use oral or parenteral antibiotics should be based on results regarding microorganism sensitivity, patient compliance, infectious disease consultation, and the surgeon's experience. A suppressive antibiotic regimen should be directed by the results of cultures. Standard operative treatment is not feasible for all patients because of the functional impairment caused by the disease, the reconstructive operations, and the metabolic consequences of an aggressive therapy regimen. Operative treatment includes debridement, obliteration of dead space, restoration of blood supply, adequate soft-tissue coverage, stabilization, and reconstruction.

Modulation of fibronectin adhesins and other virulence factors in a teicoplanin-resistant derivative of methicillin-resistant Staphylococcus aureus

The impact of glycopeptide resistance on the molecular regulation of Staphylococcus aureus virulence and attachment to host tissues is poorly documented. We compared stable teicoplanin-resistant methicillin-resistant S. aureus (MRSA) strain 14-4 with its teicoplanin-susceptible MRSA parent, strain MRGR3, which exhibits a high degree of virulence in a rat model of chronic foreign body MRSA infection. The levels of fibronectin-mediated adhesion and surface display of fibronectin-binding proteins were higher in teicoplanin-resistant strain 14-4 than in its teicoplanin-susceptible parent or a teicoplanin-susceptible revertant (strain 14-4rev) that spontaneously emerged during tissue cage infection. Quantitative reverse transcription-PCR (qRT-PCR) showed four- and twofold higher steady-state levels of fnbA and fnbB transcripts, respectively, in strain 14-4 than in its teicoplanin-susceptible counterparts. Analysis of global regulatory activities by qRT-PCR revealed a strong reduction in the steady-state levels of RNAIII and RNAII in the teicoplanin-resistant strain compared to in its teicoplanin-susceptible counterparts. In contrast, sarA mRNA levels were more than fivefold higher in strain 14-4 than in MRGR3 and 14-4rev. Furthermore, the alternative transcription factor sigma B had a higher level of functional activity in the teicoplanin-resistant strain than in its teicoplanin-susceptible counterparts, as evidenced by significant increases in both the sigma B-dependent asp23 mRNA levels and the sarA P3 promoter-derived transcript levels, as assayed by qRT-PCR and Northern blotting, respectively. These data provide further evidence that the emergence of glycopeptide resistance is linked by still poorly understood molecular pathways with significant pleiotropic changes in the expression and regulation of some major virulence genes. These molecular and phenotypic changes may have a profound impact on the bacterial adhesion and colonization properties of such multiresistant organisms.

Integrin-mediated invasion of Staphylococcus aureus into human cells requires Src family protein-tyrosine kinases

Staphylococcus aureus, a common cause of nosocomial infections, is able to invade eukaryotic cells by indirectly engaging beta1 integrin-containing host receptors, whereas non-pathogenic Staphylococcus carnosus is not invasive. Here, we identify intracellular signals involved in integrin-initiated internalization of S. aureus. In particular, the host cell actin cytoskeleton and Src family protein-tyrosine kinases (PTKs) are essential to mediate S. aureus invasion. Src PTKs are activated in response to pathogenic S. aureus, but not S. carnosus. In addition, pharmacological and genetic interference with Src PTK function reduces bacterial internalization. Importantly, Src PTK-deficient cells are resistant to S. aureus invasion, demonstrating the essentiality of host Src PTKs in integrin-mediated uptake of this pathogen.

Acute septic arthritis

Acute septic arthritis may develop as a result of hematogenous seeding, direct introduction, or extension from a contiguous focus of infection. The pathogenesis of acute septic arthritis is multifactorial and depends on the interaction of the host immune response and the adherence factors, toxins, and immunoavoidance strategies of the invading pathogen. Neisseria gonorrhoeae and Staphylococcus aureus are used in discussing the host-pathogen interaction in the pathogenesis of acute septic arthritis. While diagnosis rests on isolation of the bacterial species from synovial fluid samples, patient history, clinical presentation, laboratory findings, and imaging studies are also important. Acute nongonococcal septic arthritis is a medical emergency that can lead to significant morbidity and mortality. Therefore, prompt recognition, rapid and aggressive antimicrobial therapy, and surgical treatment are critical to ensuring a good prognosis. Even with prompt diagnosis and treatment, high mortality and morbidity rates still occur. In contrast, gonococcal arthritis is often successfully treated with antimicrobial therapy alone and demonstrates a very low rate of complications and an excellent prognosis for full return of normal joint function. In the case of prosthetic joint infections, the hardware must be eventually removed by a two-stage revision in order to cure the infection.

In vitro interactions of biomedical polyurethanes with macrophages and bacterial cells

Three commercial medical-grade polyurethanes (PUs), a poly-ether-urethane (Pellethane), and two poly-carbonate-urethanes, the one aromatic (Bionate) and the other aliphatic (Chronoflex), were tested for macrophages and bacterial cells adhesion, in the presence or absence of adhesive plasma proteins. All the experiments were carried out on PUs films obtained by solvent casting. The wettability of these films was analysed by measuring static contact angles against water. The ability of the selected PUs to adsorb human fibronectin (Fn) and fibrinogen (Fbg) was checked by ELISA with biotin-labelled proteins. All PUs were able to adsorb Fn and Fbg (Fn > Fbg). Fn adsorption was in the order: Pellethane > Chronoflex > Bionate, the highest Fbg adsorption being detected onto Bionate (Bionate > Chronoflex > Pellethane). The human macrophagic line J111, and the two main bacterial strains responsible for infection in humans (Staphylococcus aureus Newman and Staphylococcus epidermidis 14852) were incubated in turn with the three PUs, uncoated or coated with plasma proteins. No macrophage or bacterial adhesion was observed onto uncoated PUs. PUs coated with plasma, Fn or Fbg promoted bacterial adhesion (S. aureus > S. epidermidis), whereas macrophage adhered more onto PUs coated with Fn or plasma. The coating with Fbg did not promote cell adhesion. Pellethane showed the highest macrophage activation (i.e. spreading), followed, in the order, by Bionate and Chronoflex.

Reassessing the role of Staphylococcus aureus clumping factor and fibronectin-binding protein by expression in Lactococcus lactis

Since Staphylococcus aureus expresses multiple pathogenic factors, studying their individual roles in single-gene-knockout mutants is difficult. To circumvent this problem, S. aureus clumping factor A (clfA) and fibronectin-binding protein A (fnbA) genes were constitutively expressed in poorly pathogenic Lactococcus lactis using the recently described pOri23 vector. The recombinant organisms were tested in vitro for their adherence to immobilized fibrinogen and fibronectin and in vivo for their ability to infect rats with catheter-induced aortic vegetations. In vitro, both clfA and fnbA increased the adherence of lactococci to their specific ligands to a similar extent as the S. aureus gene donor. In vivo, the minimum inoculum size producing endocarditis in > or =80% of the rats (80% infective dose [ID80]) with the parent lactococcus was > or =10(7) CFU. In contrast, clfA-expressing and fnbA-expressing lactococci required only 10(5) CFU to infect the majority of the animals (P < 0.00005). This was comparable to the infectivities of classical endocarditis pathogens such as S. aureus and streptococci (ID80 = 10(4) to 10(5) CFU) in this model. The results confirmed the role of clfA in endovascular infection, but with a much higher degree of confidence than with single-gene-inactivated staphylococci. Moreover, they identified fnbA as a critical virulence factor of equivalent importance. This was in contrast to previous studies that produced controversial results regarding this very determinant. Taken together, the present observations suggest that if antiadhesin therapy were to be developed, at least both of the clfA and fnbA products should be blocked for the therapy to be effective.

A simple infection model using pre-colonized implants to reproduce rat chronic Staphylococcus aureus osteomyelitis and study antibiotic treatment

Staphylococcus aureus biofilms formed on medical implants represent a serious problem, being difficult to eradicate with antibiotic therapy and leading to chronic infections. Simplified in vivo and in vitro antibiotic susceptibility assays using biofilm bacteria are needed. In this work, a novel chronic osteomyelitis infection model was developed in rats in the absence of bacterial suspension, requiring the use of only 10(6) bacteria in biofilms at the site of surgery, with a full success in reproducing infection. Stainless-steel implants pre-colonized for 12 h with a highly adherent S. aureaus isolate were introduced into the rat tibiae. In animals not submitted to antibiotic treatment, infection was found in the implants and spread to bone in all cases, indicating the high efficacy of the model to reproduce osteomyelitis. The effect of a 21-day treatment with cefuroxime, vancomycin, tobramycin or ciprofloxacin on infection was studied in this model 42 days after surgery. Bone colonization was inhibited by vancomycin and cefuroxime. Cefuroxime (the most efficient antibiotic, able to sterilize 1 out of 8 implants) reduced the number of bacteria in biofilms adhered to implants at a higher extent than vancomycin, trobramycin and ciprofloxacin. Analogous observations were made in this work in vivo and in vitro on the relative antibiotic efficacy against S. aureus biofilm bacteria. suggesting the usefulness of both tests as a potential tool to study antibiotic suceptibility, and the need for new antimicrobials against these bacteria.

Collagen and fibronectin binding in experimental staphylococcal osteomyelitis

A new mouse model of locally induced osteomyelitis was used to study the importance for pathogenicity of the specific binding ability of Staphylococcus aureus to collagen and fibronectin. This method appears to be convenient, reproducible, and suitable for large-scale experiments. In contrast to previous studies in experimental arthritis and endocarditis models, no difference in infection rates was found between the strains deficient in binding to collagen compared with the corresponding adherence-proficient strains. However, fibronectin binding ability in this model, in contrast to the endocarditis model, is thought to enhance the microorganisms' capacity to establish an infection. Infections caused by the fibronectin-binding strain also are thought to be clinically more aggressive than those caused by the nonbinding strain. Specific adherence mechanisms are thought to be operative in the pathogenesis of biomaterial associated osteomyelitis, and an improved understanding of such mechanisms may have an important prophylactic and therapeutic impact.

Pathophysiology of chronic bacterial osteomyelitis. Why do antibiotics fail so often?

In this review the pathophysiology of chronic bacterial osteomyelitis is summarised, focusing on how bacteria succeed so often in overcoming both host defence mechanisms and antibiotic agents. Bacteria adhere to bone matrix and orthopaedic implants via receptors to fibronectin and to other structural proteins. They subsequently elude host defences and antibiotics by "hiding" intracellularly, by developing a slimy coat, or by acquiring a very slow metabolic rate. The presence of an orthopaedic implant also causes a local polymorphonuclear cell defect, with decreased ability to kill phagocytosed bacteria. Osteolysis is determined locally by the interaction of bacterial surface components with immune system cells and subsequent cytokine production. The increasing development of antibiotic resistance by Staphylococcus aureus and S epidermidis will probably make conservative treatment even less successful than it is now. A close interaction between orthopaedic surgeons and physicians, with combined medical and operative treatment, is to be commended.

Clinical isolates of Staphylococcus aureus exhibit diversity in fnb genes and adhesion to human fibronectin

OBJECTIVES

The fibronectin-binding proteins (FnBPs) of Staphylococcus aureus are involved in the pathogenesis of infection, but their characteristics in clinical isolates are incompletely defined. The aim of this study was to evaluate phenotypic and genotypic characteristics of the FnBPs of a large collection of recent isolates.

METHODS

The adherence of 163 S. aureus isolates to immobilized fibronectin was compared with that of S. aureus 8325-4 using a microtitre assay. The presence of the genes encoding the fibronectin-binding proteins FnBPA and FnBPB was evaluated by Southern dot blot using probes specific for region A of fnbA or fnbB.

RESULTS

The adherence of clinical isolates to fibronectin (expressed as a percentage of the mean adherence of S. aureus 8325-4) was 56%-125% for 155 isolates (95%), and less than 20% for eight isolates (5%). Adherence of the bacterial group associated with orthopaedic implant-associated infection was significantly greater than that for isolates associated with nasal carriage, endocarditis, or septic arthritis/osteomyelitis. Southern dot blot demonstrated that 126/163 isolates had two genes (77%) and 37/163 had one detectable gene (23%). There was no difference in adherence between isolates with one or two fnb, but isolates associated with invasive disease (endocarditis or primary septic arthritis and/or osteomyelitis) were more likely to have two genes.

CONCLUSIONS

These data demonstrate diversity in the FnBPs of clinical isolates of S. aureus. The findings suggest that the interplay between pathogenesis and a single virulence determinant is unlikely to be a uniform process across a spectrum of infections. This confirms the need to extend the study of staphylococcal pathogenesis from the laboratory to non-uniform populations of clinically relevant isolates.

Analysis of posterior spinal wiring in a validated rabbit model

Mamillary and spinous process base wiring did not improve L5-L6 posterolateral fusion rate, stiffness, or strength in a previously established rabbit model. Specimen radiography significantly underestimated fusion rate when compared with manual palpation (37% versus 68%). Fused specimens were significantly stiffer (67.2 N/mm versus 41.1 N/mm) and stronger (177 N versus 121 N) in tension than were nonfused specimens. Deep wound infection, detected only at the time of sacrifice, apparently was more common with internal fixation (43% versus 21%). Noninfected specimens were significantly stiffer (63.3 N/mm versus 43.0 N/mm) and stronger (176 N versus 107 N) than were infected specimens.

Inhibition by heparin and derivatized dextrans of Staphylococcus epidermidis adhesion to in vitro fibronectin-coated or explanted polymer surfaces

The ability of Staphylococcus aureus to recognize several extracellular matrix or plasma proteins (e.g., fibrinogen, fibronectin, and collagen) promotes bacterial attachment to artificial surfaces. Whereas most S. aureus clinical isolates elaborate a wide repertoire of bacterial surface receptors' called adhesins, exhibiting specific binding of individual host proteins, S. epidermidis is lacking most of such protein adhesins. To document the interactions between S. epidermidis and various surface-adsorbed proteins, we first compared promotion of bacterial attachment by seven purified human proteins immobilized onto poly(methyl methacrylate) (PMMA) coverslips. Only two of them, namely fibronectin and fibrinogen, exhibited adhesion-promoting activities. In the presence of native heparin or two functionalized dextrans (CMDBS for Carboxy Methyl, Benzylamide sulfonate/sulfate), a dose-dependent inhibition of S. epidermidis adhesion to fibronectin-coated, but not to fibrinogen-coated surfaces was observed. The inhibitory effects of each CMDBS were much stronger than that of native heparin. In contrast, a control highly negatively charged, dextran exclusively substituted with carboxy methyl groups exerted no inhibition on S. epidermidis adhesion. To evaluate how CMDBS could interfere with S. epidermidis attachment to coverslips coated in vivo with extracellular matrix components, we also tested PMMA surfaces retrieved from tissue cages subcutaneously implanted in guinea pigs. Each CMDBS, but not heparin, strongly inhibited S. epidermidis adhesion to explanted coverslips, even in the presence of tissue cage fluid. In conclusion, fibronectin plays an important role in promoting S. epidermidis attachment to implanted biomaterials. Furthermore, S. epidermidis adhesion to fibronectin-coated or implanted biomaterials can be efficiently blocked in vitro by CMDBS.

Identification of plasma proteins adsorbed on hemodialysis tubing that promote Staphylococcus aureus adhesion

Risk factors for Staphylococcus aureus infections in patients undergoing hemodialysis include underlying disease, material-induced host defects, and the presence of vascular access catheters. To determine the specific contribution of various potentially adsorbed plasma components in promoting S aureus adhesion to shunt tubing during chronic hemodialysis, we quantified their respective amounts by Western immunoblotting and densitometry and estimated their individual adhesion-promoting activities with specific adhesion-modified bacterial mutants. Fibrinogen, which was the only component consistently present in tubing protein extracts from all patients, was adsorbed in significantly higher amounts on predialyzer than on postdialyzer tubing segments. In contrast, fibronectin and von Willebrand factor were irregularly present in patients' tubing, whereas vitronectin or thrombospondin remained undetectable in all samples. The contribution of fibrinogen in promoting S aureus attachment to hemodialysis tubing was demonstrated by (1) the significantly lower adhesion of a cIfA mutant of strain Newman compared with its parent; (2) the increased attachment of strain 8325-4 after complementation with the cloned cIfA gene on the multicopy plasmid pCF4; and (3) the general tendency for strains Newman and 8325-4(pCF4) to express higher attachment on predialyzer compared with postdialyzer tubing segments in relationship with the higher content of fibrinogen on the former material. However, the specific S aureus attachment-promoting activity of both prefilter and postfilter tubing-adsorbed fibrinogen were much lower than that of the native in vitro-adsorbed protein and may reflect masking or inactivation of the in vivo-adsorbed protein by unknown mechanisms.

Extracellular-matrix-binding proteins as targets for the prevention of Staphylococcus aureus infections

Staphylococcal infections cause a number of serious diseases, ranging from acute septicaemia to chronic problems such as osteomyelitis and septic arthritis. Resistance to antibiotics is a growing problem and has re-ignited interest in vaccines and in passive immunization with antibodies. Natural infections and vaccines based on whole bacteria lead to poor antibody responses, but recent research using animal models of several staphylococcal diseases reveals that vaccines based on recombinant staphylococcal extracellular-matrix-binding proteins are much more protective. Passive immunization with antibodies against one of these proteins (collagen-binding protein) also shows promise in a mouse model of sepsis.

Contamination of the medullary canal following pin-tract infection

We developed an ovine model of an external-fixator pin-tract infection. With use of a novel method of tissue sampling, infection of the medullary canal was confirmed in all (10 of 10) external-fixator pins that were contaminated with Staphylococcus aureus after they were inserted. In addition, all (five of five) adjacent, uncontaminated pins became infected. We demonstrated that pin-tract infection can be difficult to diagnose clinically, despite gross infection of the tract, and that bacteria can spread within the medulla. Three of the infected pins (20%) did not appear clinically infected, were not loose, and were normal on radiographs after 1 week. Staphylococcus aureus was isolated from the medulla around all 15 pin tracts, and nine other organisms were isolated from the tracts. Despite the presence of infection, the majority of the pins remained well fixed in the bone after 2 weeks.

Osteomyelitis

Despite significant progress in antibiotic therapy and orthopedic surgery, osteomyelitis remains a difficult-to-treat infection that is often associated with recurrence. In this paper we summarize the most recent developments in understanding the pathogenesis of this complex disease, as well as novel means for its diagnosis and treatment.

Pathophysiology of posttraumatic osteomyelitis

Understanding the pathophysiology of posttraumatic osteomyelitis is crucial as researchers attempt to meet the challenge of developing more effective strategies for the management and prevention of this infection. Some aspects of pathogenesis have been well described, including the important roles of the extent of soft tissue injury, bacterial attachment to necrotic bone and fixation devices, and bacterial contamination at the time of injury. More recently, the importance of early wound coverage in preventing osteomyelitis has been emphasized. Now some of the cellular interactions that promote infection and tissue damage are beginning to be understood. Trauma can have deleterious effects on host response to infection through its activation of certain cytokines. These cytokines, mainly produced by cells of the immune system, regulate the action of polymorphonuclear leukocytes, macrophages, and lymphocytes. Bacteria have been shown to use diverse tactics to initiate and maintain infection that lead to host defense impairment, decreased efficacy of antibiotics, and direct tissue damage. New insights into the pathophysiology of osteomyelitis may lead to the innovative therapeutic approaches needed to improve the standard of care for this infection.