Role of coagulase in a murine model of hematogenous pulmonary infection induced by intravenous injection of Staphylococcus aureus enmeshed in agar beads

Galangin as a direct inhibitor of vWbp protects mice from Staphylococcus aureus-induced pneumonia

The surge in multidrug resistance in Staphylococcus aureus (S. aureus) and the lag in antibiotic discovery necessitate the development of new anti‐infective strategies to reduce S. aureus infections. In S. aureus, von Willebrand factor‐binding protein (vWbp) is not only the main coagulase that triggers host prothrombin activation and formation of fibrin cables but also bridges the bacterial cell wall and von Willebrand factor, thereby allowing S. aureus to bind to platelets and endothelial cells, playing a vital role in pathogenesis of S. aureus infections. Here, we have identified that galangin, a bioactive compound found in honey and Alpinia officinarum Hance, is a potent and direct inhibitor of vWbp by coagulation activity inhibition assay, thermal shift assay and biolayer interferometry assay. Molecular dynamic simulations and verification experiments revealed that the Trp‐64 and Leu‐69 residues are necessary for the binding of galangin to vWbp. Significantly, galangin attenuated S. aureus virulence in a mouse S. aureus‐induced pneumonia model. In addition, we also identified that galangin can enhance the therapeutic effect of latamoxef on S. aureus‐induced pneumonia. Taken together, the results suggest that galangin may be used for the development of therapeutic drugs or utilized as adjuvants to combine with antibiotics to combat S. aureus‐related infections.

Staphylococcus aureus in poultry, with special emphasis on methicillin-resistant strain infection: A comprehensive review from one health perspective

Staphylococcus aureus is a Gram-positive coccus normally present on the skin and internal organs of animals, birds, and humans. Under certain conditions, S. aureus could produce septicemia and affection of the skin, joints, and heart, as well as sepsis and death. The pathogenicity of S. aureus is associated with the presence of some virulent surface proteins and the production of some virulent toxins and enzymes. This pathogen is considered one of the most important and worldwide foodborne causes as it is incriminated in most cases of food poisoning. The hazardous use of antibiotics in the veterinary field leads to the development of multidrug-resistant S. aureus strains that can be transmitted to humans. The incidence of methicillin-resistant S. aureus (MRSA) strains has increased globally. These resistant strains have been detected in live animals, poultry, and humans. In addition, retail animal products, especially those of avian origin, are considered the main source of MRSA strains that can be easily transmitted to humans. MRSA infection is regarded as nosocomial or occupational. Humans get infected with MRSA strains through improper handling or preparation of contaminated animals or poultry carcasses or improper cooking with contaminated meat. Live birds also can transmit MRSA to close-contact workers in poultry farms. Transmission of MRSA infection in hospitals is from an infected individual to a healthy one. Prevention and control of MRSA are based on the application of hygienic measures in farms as well as proper processing, handling, and cooking of retail poultry products. The cooperation between veterinary and human practitioners is a must to avoid the possibility of zoonotic transmission. Accordingly, this review focused on the sources and transmission of MRSA infection, virulence and resistance factors, incidence and prevalence in poultry and different products, antibiotic resistance, and prevention and control strategies.

Isovitexin Is a Direct Inhibitor of Staphylococcus aureus Coagulase

Staphylococcus aureus (S. aureus) is a major pathogen that causes human pneumonia, leading to significant morbidity and mortality. S. aureus coagulase (Coa) triggers the polymerization of fibrin by activating host prothrombin, which then converts fibrinogen to fibrin and contributes to S. aureus pathogenesis and persistent infection. In our research, we demonstrate that isovitexin, an active traditional Chinese medicine component, can inhibit the coagulase activity of Coa but does not interfere with the growth of S. aureus. Furthermore, we show through thermal shift and fluorescence quenching assays that isovitexin directly binds to Coa. Dynamic simulation and structure-activity relationship analyses suggest that V191 and P268 are key amino acid residues responsible for the binding of isovitexin to Coa. Taken together, these data indicate that isovitexin is a direct Coa inhibitor and a promising candidate for drug development against S. aureus infection.

An ex vivo cystic fibrosis model recapitulates key clinical aspects of chronic Staphylococcus aureus infection

Staphylococcus aureus is the most prevalent organism isolated from the airways of people with cystic fibrosis (CF), predominantly early in life. Yet its role in the pathology of lung disease is poorly understood. In mice, and many experiments using cell lines, the bacterium invades cells or interstitium, and forms abscesses. This is at odds with the limited available clinical data: interstitial bacteria are rare in CF biopsies and abscesses are highly unusual. Bacteria instead appear to localize in mucus plugs in the lumens of bronchioles. We show that, in an established ex vivo model of CF infection comprising porcine bronchiolar tissue and synthetic mucus, S. aureus demonstrates clinically significant characteristics including colonization of the airway lumen, with preferential localization as multicellular aggregates in mucus, initiation of a small colony variant phenotype and increased antibiotic tolerance of tissue-associated aggregates. Tissue invasion and abscesses were not observed. Our results may inform ongoing debates relating to clinical responses to S. aureus in people with CF.

Baicalein mediates protection against Staphylococcus aureus-induced pneumonia by inhibiting the coagulase activity of vWbp

The emergence and spread of multidrug-resistant Staphylococcus aureus (S. aureus) necessitate the research on therapeutic tactics which are different from classical antibiotics in overcoming resistance andtreatinginfections. In S. aureus, von Willebrand factor-binding protein (vWbp) is one of the key virulence determinants because it mediates not only the activation of thrombin to convert fibrinogen to fibrin, thereby enabling S. aureus to escape from the host immune clearance, but also the adhesion of S. aureus to host cells. Thus, vWbp is regarded as a promising druggable target to treat S. aureus-associated infections. Here we identify that baicalein, a natural compound isolated from the Chinese herb Scutellaria baicalensis, can effectively block the coagulase activity of vWbp without inhibiting the growth of the bacteria. Through thermal shift and fluorescence quenching assays, we demonstrated that baicalein directly binds to vWbp. Molecular dynamics simulations and mutagenesis assays revealed that the Asp-75 and Lys-80 residues are necessary for baicalein binding to vWbp. Importantly, we demonstrated that baicalein treatment attenuates the virulence of S. aureus and protects mice from S. aureus-induced lethal pneumonia. In addition, baicalein can improve the therapeutic effect of penicillin G by 75% in vivo. These findings indicate that baicalein might be developed as a promising therapeutic agent against drug-resistant S. aureus infections.

Animal Models for Drug Development for MRSA

One of the foremost challenges of drug discovery in any therapeutic area is that of solidifying the correlation between in vitro activity and clinical efficacy. Between these is the confirmation that affecting a particular target in vivo will lead to a therapeutic benefit. In antibacterial drug discovery, there is a key advantage from the start, since the targets are bacteria-therefore, it is simple to ascertain in vitro whether a drug has the desired effect, i.e., bacterial cell inhibition or killing, and to understand the mechanism by which that occurs. The downstream criteria, whether a compound reaches the infection site and achieves appropriately high levels to affect bacterial viability, can be evaluated in animal models of infection. In this way animal models of infection can be a highly valuable and predictive bridge between in vitro drug discovery and early clinical evaluation.The Gram-positive pathogen Staphylococcus aureus causes a wide variety of infections in humans (Archer, Clin Infect Dis 26:1179-1181, 1998), and has been said to be able to infect every tissue type. Fortunately, over the years a great deal of effort has been expended toward developing infection models in rodents using this organism, with good success. This chapter describes the advantages, setups, and outcome measurements of the rodent models most used in drug discovery for S. aureus. Mouse models will be the focus of this chapter, as they are the most economical and thus most commonly used, but a rat infection model is included as well.

Multimodal Tracking of Controlled Staphylococcus aureus Infections in Mice

There is a need to develop diagnostic and analytical tools that allow noninvasive monitoring of bacterial growth and dissemination in vivo. For such cell-tracking studies to hold translational value to controlled human infections, in which volunteers are experimentally colonized, they should not require genetic modification, and they should allow tracking over a number of replication cycles. To gauge if an antimicrobial peptide tracer, 99mTc-UBI29-41-Cy5, which contains both a fluorescent and a radioactive moiety, could be used for such in vivo bacterial tracking, we performed longitudinal imaging of a thigh-muscle infection with 99mTc-UBI29-41-Cy5-labeled Staphylococcus aureus. Mice were imaged using SPECT and fluorescence-imaging modalities at various intervals during a 28 h period. Biodistribution analyses were performed to quantitate radioactivity in the abscess and other tissues. SPECT and fluorescence imaging in mice showed clear retention of the 99mTc-UBI29-41-Cy5-labeled bacteria following inoculation in the thigh muscle. Despite bacterial replication, the signal intensity in the abscess only modestly decreased within a 28 h period: 52% of the total injected radioactivity per gram of tissue (%ID/g) at 4 h postinfection (pi) versus 44%ID/g at 28 h pi (15% decrease). After inoculation, a portion of the bacteria disseminated from the abscess, and S. aureus cultures were obtained from radioactive urine samples. Bacterial staining with 99mTc-UBI29-41-Cy5 allowed noninvasive bacterial-cell tracking during a 28 h period. Given the versatility of the presented bacterial-tracking method, we believe that this concept could pave the way for precise imaging capabilities during controlled-human-infection studies.

An Inhibitory Effect of Dryocrassin ABBA on Staphylococcus aureus vWbp That Protects Mice From Pneumonia

Von Willebrand factor-binding protein (vWbp), secreted by Staphylococcus aureus (S. aureus), can activate host prothrombin, convert fibrinogen to fibrin clots, induce blood clotting, and contribute to pathophysiology of S. aureus-related diseases, including infective endocarditis, staphylococcal sepsis and pneumonia. Therefore, vWbp is an promising drug target in the treatment of S. aureus-related infections. Here, we report that dryocrassin ABBA (ABBA), a natural compound derived from Dryopteris crassirhizoma, can significantly inhibit the coagulase activity of vWbp in vitro by directly interacting with vWbp without killing the bacteria or inhibiting the expression of the vWbp. Using molecular dynamics simulations, we demonstrate that ABBA binds to the "central cavity" in the elbow of vWbp by interacting with Arg-70, His-71, Ala-72, Gly-73, Tyr-74, Glu-75, Tyr-83, and Gln-87 in vWbp, thus interfering with the binding of vWbp to prothrombin. Furthermore, in vivo studies demonstrated that ABBA can attenuate injury and inflammation of mouse lung tissues caused by S. aureus and increase survival of mice. Together these findings indicate that ABBA is a promising lead drug for the treatment of S. aureus-related infections. This is the first report of potential inhibitor which inhibit the coagulase activity of vWbp by directly interacting with vWbp.

In vivo efficacy and pharmacokinetics of bi-aryl oxazolidinone RBx 11760 loaded polylactic acid-polyethylene glycol nanoparticles in mouse hematogenous bronchopneumonia and rat groin abscess caused by Staphylococcus aureus

RBx 11760 is a bi-aryl oxazolidinone antibacterial agent active against Staphylococcus aureus but has poor solubility. Here we have encapsulated RBx 11760 in PLA-PEG NPs with an aim to improve physicochemical, pharmacokinetics and in vivo efficacy. The average size and zeta potential of RBx 11760 loaded NPs were found to be 106.4 nm and -22.2 mV, respectively. The absolute size of nanoparticles by HRTEM was found to be approximately 80 nm. In vitro antibacterial agar well diffusion assay showed clear zone of inhibition of bacterial growth. In pharmacokinetic study, nanoparticle showed 4.6-fold and 7-fold increase in AUC_inf and half-life, respectively, as compared to free drug. RBx 11760 nanoparticle significantly reduced bacterial counts in lungs and improved the survival rate of immunocompromised mice as compared to free drugs. Thus, RBx 11760 loaded nanoparticles have strong potential to be used as nanomedicine against sensitive and drug resistant Staphylococcus aureus infections.

Computed Tomography Features of Septic Pulmonary Embolism Caused by Klebsiella pneumoniae Liver Abscess Associated With Extrapulmonary Metastatic Infection

OBJECTIVES

The aims of the study were to investigate the computed tomography (CT) features and clinical course of septic pulmonary embolism (SPE) caused by Klebsiella pneumoniae liver abscess (KPLA) and to explore the possible mechanism underlying the spread of infection.

METHODS

Twenty-one patients with KPLA-induced SPE admitted to our hospital between January 2010 and May 2015 were evaluated. According to the presence or absence of extrapulmonary metastatic infection (EMI), they were divided into EMI and non-EMI groups and clinical and CT features of the 2 groups were compared. Hepatic vein thrombophlebitis was evaluated on liver CT images. Chest CT features included nodules, wedge-shaped lesions, ground-glass opacity, consolidation, cavitation, feeding vessel sign, pleural effusion, and lymphadenopathy.

RESULTS

All the vessels within the so-called feeding vessel sign were confirmed as pulmonary veins by multiplanar reconstruction, so we used an alternative name draining vessel sign (DVS) instead. Peripheral nodules, DVS, and consolidation were the main CT features of KPLA-induced SPE. Peripheral nodules and DVS were more frequently seen in the EMI group than in the non-EMI group (P = 0.019 and 0.008, respectively). Five of 8 patients with hepatic vein thrombophlebitis had lung consolidation, whereas only 3 of 13 patients without hepatic vein thrombophlebitis had lung consolidation, although the difference was not significant (P = 0.09).

CONCLUSIONS

Multiple pulmonary nodules and DVS were associated with EMI. Hepatic and pulmonary vein invasion are possible causes underlying the metastatic spread of infection.

Staphylococcus aureus Aggregation and Coagulation Mechanisms, and Their Function in Host-Pathogen Interactions

The human commensal bacterium Staphylococcus aureus can cause a wide range of infections ranging from skin and soft tissue infections to invasive diseases like septicemia, endocarditis, and pneumonia. Muticellular organization almost certainly contributes to S. aureus pathogenesis mechanisms. While there has been considerable focus on biofilm formation and its role in colonizing prosthetic joints and indwelling devices, less attention has been paid to nonsurface-attached group behavior like aggregation and clumping. S. aureus is unique in its ability to coagulate blood, and it also produces multiple fibrinogen-binding proteins that facilitate clumping. Formation of clumps, which are large, tightly packed groups of cells held together by fibrin(ogen), has been demonstrated to be important for S. aureus virulence and immune evasion. Clumps of cells are able to avoid detection by the host's immune system due to a fibrin(ogen) coat that acts as a shield, and the size of the clumps facilitates evasion of phagocytosis. In addition, clumping could be an important early step in establishing infections that involve tight clusters of cells embedded in host matrix proteins, such as soft tissue abscesses and endocarditis. In this review, we discuss clumping mechanisms and regulation, as well as what is known about how clumping contributes to immune evasion.

Self-enhanced targeted delivery of a cell wall- and membrane-active antibiotics, daptomycin, against staphylococcal pneumonia

Considering that some antibacterial agents can identify the outer structure of pathogens like cell wall and/or cell membrane, we explored a self-enhanced targeted delivery strategy by which a small amount of the antibiotic molecules were modified on the surface of carriers as targeting ligands of certain bacteria while more antibiotic molecules were loaded inside the carriers, and thus has the potential to improve the drug concentration at the infection site, enhance efficacy and reduce potential toxicity. In this study, a novel targeted delivery system against methicillin-resistant Staphylococcus aureus (MRSA) pneumonia was constructed with daptomycin, a lipopeptide antibiotic, which can bind to the cell wall of S. aureus via its hydrophobic tail. Daptomycin was conjugated with N-hydroxysuccinimidyl–polyethylene glycol–1,2-distearoyl-sn-glycero-3-phosphoethanolamine to synthesize a targeting compound (Dapt–PEG–DSPE) which could be anchored on the surface of liposomes, while additional daptomycin molecules were encapsulated inside the liposomes. These daptomycin-modified, daptomycin-loaded liposomes (DPD-L[D]) showed specific binding to MRSA as detected by flow cytometry and good targeting capabilities in vivo to MRSA-infected lungs in a pneumonia model. DPD-L[D] exhibited more favorable antibacterial efficacy against MRSA than conventional PEGylated liposomal daptomycin both in vitro and in vivo. Our study demonstrates that daptomycin-modified liposomes can enhance MRSA-targeted delivery of encapsulated antibiotic, suggesting a novel drug delivery approach for existing antimicrobial agents.

Antimicrobial and immunomodulatory effects of tedizolid against methicillin-resistant Staphylococcus aureus in a murine model of hematogenous pulmonary infection

Tedizolid (TZD) is a second-generation oxazolidinone and demonstrates potent in-vitro activity against multidrug-resistant Gram-positive bacteria. Phase III studies in patients with acute bacterial skin and skin structure infections (ABSSSI) have demonstrated the non-inferiority of TZD to linezolid (LZD). However, there are only a few studies that show the effect of TZD in pulmonary infections. In this study, we investigated the effect of TZD in a murine model of hematogenous pulmonary infection caused by methicillin-resistant Staphylococcus aureus (MRSA). The mice were treated either twice daily with saline (control), 25mg/kg of vancomycin (low-VAN), 110mg/kg of vancomycin (high-VAN), 120mg/kg of LZD or once daily with 20mg/kg of TZD. As compared to the control, the low- and high-VAN treatment groups, LZD and TZD significantly improved the survival rate, reduced the bacterial count in the lungs. Furthermore, TZD decreased the area of central bacterial colony zone (CBCZ) at 36h post-inoculation, compared with the control. In addition, we investigated the immunomodulatory effect of TZD by evaluating the plasma concentrations of the inflammatory cytokines. Although there were no significant differences in the bacterial count in the lungs amongst the drugs at 26h post-inoculation, TZD and LZD significantly improved the plasma concentrations of TNF-alpha, IL-6 and MIP-2, in comparison with the control. In this study, both TZD and LZD demonstrated antimicrobial and immunomodulatory efficacy in a murine model of hematogenous pulmonary infection caused by MRSA.

Fibrinogen Is at the Interface of Host Defense and Pathogen Virulence in Staphylococcus aureus Infection

Fibrinogen not only plays a pivotal role in hemostasis but also serves key roles in antimicrobial host defense. As a rapidly assembled provisional matrix protein, fibrin(ogen) can function as an early line of host protection by limiting bacterial growth, suppressing dissemination of microbes to distant sites, and mediating host bacterial killing. Fibrinogen-mediated host antimicrobial activity occurs predominantly through two general mechanisms, namely, fibrin matrices functioning as a protective barrier and fibrin(ogen) directly or indirectly driving host protective immune function. The potential of fibrin to limit bacterial infection and disease has been countered by numerous bacterial species evolving and maintaining virulence factors that engage hemostatic system components within vertebrate hosts. Bacterial factors have been isolated that simply bind fibrinogen or fibrin, promote fibrin polymer formation, or promote fibrin dissolution. Staphylococcus aureus is an opportunistic gram-positive bacterium, the causative agent of a wide range of human infectious diseases, and a prime example of a pathogen exquisitely sensitive to host fibrinogen. Indeed, current data suggest fibrinogen serves as a context-dependent determinant of host defense or pathogen virulence in Staphylococcus infection whose ultimate contribution is dictated by the expression of S. aureus virulence factors, the path of infection, and the tissue microenvironment.

Animals devoid of pulmonary system as infection models in the study of lung bacterial pathogens

Biological disease models can be difficult and costly to develop and use on a routine basis. Particularly, in vivo lung infection models performed to study lung pathologies use to be laborious, demand a great time and commonly are associated with ethical issues. When infections in experimental animals are used, they need to be refined, defined, and validated for their intended purpose. Therefore, alternative and easy to handle models of experimental infections are still needed to test the virulence of bacterial lung pathogens. Because non-mammalian models have less ethical and cost constraints as a subjects for experimentation, in some cases would be appropriated to include these models as valuable tools to explore host-pathogen interactions. Numerous scientific data have been argued to the more extensive use of several kinds of alternative models, such as, the vertebrate zebrafish (Danio rerio), and non-vertebrate insects and nematodes (e.g., Caenorhabditis elegans) in the study of diverse infectious agents that affect humans. Here, we review the use of these vertebrate and non-vertebrate models in the study of bacterial agents, which are considered the principal causes of lung injury. Curiously none of these animals have a respiratory system as in air-breathing vertebrates, where respiration takes place in lungs. Despite this fact, with the present review we sought to provide elements in favor of the use of these alternative animal models of infection to reveal the molecular signatures of host-pathogen interactions.

Plasminogen activation by staphylokinase enhances local spreading of S. aureus in skin infections

BACKGROUND

Staphylococcus aureus (S. aureus) is a frequent cause of skin and soft tissue infections. A unique feature of S. aureus is the combined presence of coagulases that trigger fibrin formation and of the plasminogen activator staphylokinase (SAK). Whereas the importance of fibrin generation for S. aureus virulence has been established, the role of SAK remains unclear. We studied the role of plasminogen activation by SAK in a skin infection model in mice and evaluated the impact of alpha-2-antiplasmin (α2AP) deficiency on the spreading and proteolytic activity of S. aureus skin infections. The species-selectivity of SAK was overcome by adenoviral expression of human plasminogen. Bacterial spread and density was assessed non-invasively by imaging the bioluminescence of S. aureus Xen36.

RESULTS

SAK-mediated plasmin activity increased the local invasiveness of S. aureus, leading to larger lesions with skin disruption as well as decreased bacterial clearance by the host. Even though fibrin and bacterial surfaces protected SAK-mediated plasmin activity from inhibition by α2AP, the deficiency of α2AP resulted in increased bacterial spreading. SAK-mediated plasmin also induced secondary activation of gelatinases, shown both in vitro and in lesions from the in vivo model.

CONCLUSION

SAK contributes to the phenotype of S. aureus skin infections by enhancing bacterial spreading as a result of fibrinolytic and proteolytic activation.

Encapsulating peritoneal sclerosis: case series from a university center

BACKGROUND/AIMS

Encapsulating peritoneal sclerosis (EPS) is an often-fatal complication of long-term peritoneal dialysis (PD). We here report the clinical features of EPS in Korean PD patients from a single university center.

METHODS

The data were collected retrospectively from 606 PD patients at Kyungpook National University Hospital, between August 2001 and August 2011. The diagnosis of EPS was based on clinical signs and symptoms, and confirmed by radiological findings.

RESULTS

Eight patients (1.3%, four males) were diagnosed with EPS. The mean age of the patients was 48.5 years (range, 33 to 65). The mean duration of PD was 111.8 months (range, 23 to 186). All patients except for one had three or more episodes of peritonitis. Seven patients were diagnosed with EPS after stopping PD, and only one stayed on PD after initial diagnosis and treatment. Total parenteral nutrition and corticosteroids, in addition to tamoxifen therapy, were used to treat most of the patients, and one patient underwent surgery (adhesiolysis). The overall mortality rate was 50%.

CONCLUSIONS

EPS is a serious, life-threatening complication in patients on long-term PD. To reduce the incidence and mortality rate of EPS, careful monitoring and early diagnosis is needed.

From in vitro to in vivo Models of Bacterial Biofilm-Related Infections

The influence of microorganisms growing as sessile communities in a large number of human infections has been extensively studied and recognized for 30–40 years, therefore warranting intense scientific and medical research. Nonetheless, mimicking the biofilm-life style of bacteria and biofilm-related infections has been an arduous task. Models used to study biofilms range from simple in vitro to complex in vivo models of tissues or device-related infections. These different models have progressively contributed to the current knowledge of biofilm physiology within the host context. While far from a complete understanding of the multiple elements controlling the dynamic interactions between the host and biofilms, we are nowadays witnessing the emergence of promising preventive or curative strategies to fight biofilm-related infections. This review undertakes a comprehensive analysis of the literature from a historic perspective commenting on the contribution of the different models and discussing future venues and new approaches that can be merged with more traditional techniques in order to model biofilm-infections and efficiently fight them.

The role of staphylothrombin-mediated fibrin deposition in catheter-related Staphylococcus aureus infections

Staphylococcus aureus (S. aureus) is a frequent cause of catheter-related infections. S. aureus secretes the coagulases staphylocoagulase and von Willebrand factor-binding protein, both of which form a staphylothrombin complex upon binding to prothrombin. Although fibrinogen and fibrin facilitate the adhesion of S. aureus to catheters, the contribution of staphylothrombin-mediated fibrin has not been examined. In this study, we use a S. aureus mutant lacking both coagulases (Δcoa/vwb) and dabigatran, a pharmacological inhibitor of both staphylothrombin and thrombin, to address this question. Genetic absence or chemical inhibition of pathogen-driven coagulation reduced both fibrin deposition and the retention of S. aureus on catheters in vitro. In a mouse model of jugular vein catheter infection, dabigatran reduced bacterial load on jugular vein catheters, as well as metastatic kidney infection. Importantly, inhibition of staphylothrombin improved the efficacy of vancomycin treatment both in vitro and in the mouse model.

In vivo efficacy of daptomycin against methicillin-resistant Staphylococcus aureus in a mouse model of hematogenous pulmonary infection

Daptomycin is inactivated by pulmonary surfactant, but its effectiveness in hematogenous pulmonary infection has been poorly studied. The potential therapeutic application was evaluated in a methicillin-resistant Staphylococcus aureus (MRSA) hematogenous pulmonary infection mouse model. Compared with control results, daptomycin improved survival (P < 0.001) and decreased the number of abscesses and bacteria in the lungs (P < 0.01). Daptomycin may be an effective therapeutic option for MRSA hematogenous pulmonary infection.

Role for the fibrinogen-binding proteins coagulase and Efb in the Staphylococcus aureus-Candida interaction

Staphylococcus aureus and Candida species are increasingly coisolated from implant-associated polymicrobial infections creating an incremental health care problem. Synergistic effects between both genera seem to facilitate the formation of mixed S. aureus-Candida biofilms, which is thought to play a critical role in coinfections with these microorganisms. To identify and characterize S. aureus factors involved in the interaction with Candida species, we affinity-panned an S. aureus phage display library against Candida biofilms in the presence or absence of fibrinogen. Repeatedly isolated clones contained DNA fragments encoding portions of the S. aureus fibrinogen-binding proteins coagulase or Efb. The coagulase binds to prothrombin in a 1:1 ratio thereby inducing a conformational change and non-proteolytic activation of prothrombin, which in turn cleaves fibrinogen to fibrin. Efb has been known to inhibit opsonization. To study the role of coagulase and Efb in the S. aureus-Candida cross-kingdom interaction, we performed flow-cytometric phagocytosis assays. Preincubation with coagulase reduced the phagocytosis of Candida yeasts by granulocytes significantly and dose-dependently. By using confocal laser scanning microscopy, we demonstrated that the coagulase mediated the formation of fibrin surrounding the candidal cells. Furthermore, the addition of Efb significantly protected the yeasts against phagocytosis by granulocytes in a dose-dependent and saturable fashion. In conclusion, the inhibition of phagocytosis of Candida cells by coagulase and Efb via two distinct mechanisms suggests that S. aureus might be beneficial for Candida to persist as it helps Candida to circumvent the host immune system.

Fibrin formation by staphylothrombin facilitates Staphylococcus aureus-induced platelet aggregation

Interactions of Staphylococcus aureus (S. aureus) and platelets play an important role in the pathogenesis of intravascular infections such as infective endocarditis (IE). A typical feature of S. aureus is the ability to generate thrombin activity through the secretion of two prothrombin activating molecules, staphylocoagulase and von Willebrand factor-binding protein (vWbp), which bind to human prothrombin to form the enzymatically active staphylothrombin complex. The role of staphylothrombin in the interaction between S. aureus and platelets has not yet been studied. We found that in contrast with thrombin, staphylothrombin did not directly activate human platelets. However, the staphylothrombin-mediated conversion of fibrinogen to fibrin initiated platelet aggregation and secondary activation and facilitated S. aureus-platelet interactions. Both the genetic absence of staphylocoagulase and vWbp and pharmacological inhibition of staphylothrombin increased the lag time to aggregation, and reduced platelet trapping by S. aureus in high shear stress conditions. The combined inhibition of staphylothrombin and immunoglobulin binding to platelets completely abolished the ability of S. aureus to aggregate platelets in vitro. In conclusion, although staphylothrombin did not directly activate platelets, the formation of a fibrin scaffold facilitated bacteria-platelet interaction, and the inhibition of staphylothrombin resulted in a reduced activation of platelets by S. aureus.

Two distinct coagulase-dependent barriers protect Staphylococcus aureus from neutrophils in a three dimensional in vitro infection model

Staphylococcus aureus is a pyogenic abscess-forming facultative pathogenic microorganism expressing a large set of virulence-associated factors. Among these, secreted proteins with binding capacity to plasma proteins (e.g. fibrinogen binding proteins Eap and Emp) and prothrombin activators such as Coagulase (Coa) and vWbp are involved in abscess formation. By using a three-dimensional collagen gel (3D-CoG) supplemented with fibrinogen (Fib) we studied the growth behavior of S. aureus strain Newman and a set of mutants as well as their interaction with mouse neutrophils by real-time confocal microscopy. In 3D-CoG/Fib, S. aureus forms microcolonies which are surrounded by an inner pseudocapsule and an extended outer dense microcolony-associated meshwork (MAM) containing fibrin. Coa is involved in formation of the pseudocapsule whereas MAM formation depends on vWbp. Moreover, agr-dependent dispersal of late stage microcolonies could be observed. Furthermore, we demonstrate that the pseudocapsule and the MAM act as mechanical barriers against neutrophils attracted to the microcolony. The thrombin inhibitor argatroban is able to prevent formation of both pseudocapsule and MAM and supports access of neutrophils to staphylococci. Taken together, this model can simulate specific stages of S. aureus abscess formation by temporal dissection of bacterial growth and recruitment of immune cells. It can complement established animal infection models in the development of new treatment options.

Staphylococcus aureus is one of the most frequent pathogens causing divers localized and metastatic abscess-forming infections. Here we studied the role of the staphylocoagulases Coa and vWbp in the formation of microcolony-associated fibrin structures. By using a three-dimensional collagen gel (3D-CoG) supplemented with human fibrinogen as a growth environment for staphylococci and as a neutrophil migration matrix, we were able to demonstrate that Coa is involved in producing a fibrin-containing pseudocapsule wrapping the staphylococcal microcolony whereas vWbp is required for establishing an extended outer fibrin meshwork. The pseudocapsule and the outer meshwork hinder neutrophils from attacking the staphylococci. Addition of the thrombin inhibitor argatroban prevents conversion of fibrinogen to fibrin and thus abolishes barrier formation. This in vitro model provides us with new options to study formation as well as prevention of staphylococcal abscesses under tissue-like conditions.

Staphylococcus aureus secretes coagulase and von Willebrand factor binding protein to modify the coagulation cascade and establish host infections

Clinical isolates of Staphylococcus aureus secrete coagulases, polypeptides that bind to and activate prothrombin, thereby converting fibrinogen to fibrin and promoting the clotting of plasma or blood. Two staphylococcal products, the canonical coagulase (Coa) as well as the recently identified von Willebrand factor binding protein (vWbp), promote similar modifications of the coagulation cascade during host infection. Staphylococcal binding to fibrinogen or fibrin is an important attribute of disease pathogenesis, which leads to the formation of abscesses and bacterial persistence in host tissues and also enables the pathogen to cause lethal sepsis. Circumstantial evidence suggests that the product of coagulase activity, staphylococci captured within a fibrin meshwork, enable this pathogen to disseminate as thromboembolic lesions and to resist opsonophagocytic clearance by host immune cells. In addition, the coagulation products of staphylococci appear to display discrete differences when compared to those of thrombin-mediated coagulation, the latter representing a key innate defense mechanism against many invading pathogens. Preclinical evidence suggests that inactivation or neutralization of coagulases may prevent the pathogenesis of staphylococcal infections, a strategy that could be used to combat the current epidemic of hospital-acquired infections with drug-resistant S. aureus isolates.

Exploring Staphylococcus aureus pathways to disease for vaccine development

Staphylococcus aureus is a commensal of the human skin or nares and a pathogen that frequently causes skin and soft tissue infections as well as bacteremia and sepsis. Recent efforts in understanding the molecular mechanisms of pathogenesis revealed key virulence strategies of S. aureus in host tissues: bacterial scavenging of iron, induction of coagulation pathways to promote staphylococcal agglutination in the vasculature, and suppression of innate and adaptive immune responses. Advances in all three areas have been explored for opportunities in vaccine design in an effort to identify the critical protective antigens of S. aureus. Human clinical trials with specific subunit vaccines have failed, yet provide important insights for the design of future trials that must address the current epidemic of S. aureus infections with drug-resistant isolates (MRSA, methicillin-resistant S. aureus).

Inhibition of staphylothrombin by dabigatran reduces Staphylococcus aureus virulence

BACKGROUND

Staphylocoagulase and von Willebrand binding protein (VWbp) bind to prothrombin to form the staphylothrombin complex that converts fibrinogen into fibrin.

OBJECTIVES

To study the role of staphylothrombin and its inhibition by dabigatran on Staphylococcus aureus virulence.

METHODS

We studied the effect of staphylothrombin inhibition on bacterial attachment to polystyrene surfaces, leukocyte activation and bactericidal activity for S. aureus ATCC 25923, S. aureus Newman, and staphylocoagulase- and VWbp-negative S. aureus Newman mutants in the presence or absence of prothrombin and fibrinogen. We measured the abscess size after subcutaneous (s.c.) injection of S. aureus ATCC 25923 and S. aureus Newman, as well as an S. aureus Newman mutant strain lacking staphylocoagulase and VWbp, in mice treated with either dabigatran or placebo.

RESULTS

Staphylothrombin-mediated fibrin increased the association of S. aureus to polystyrene surfaces and reduced the bactericidal activity of leukocytes. The absence or inhibition of staphylothrombin decreased the bacterial association, enhanced leukocyte activation and reduced bacterial survival in vitro. Abscess size was smaller in mice treated with dabigatran or infected with a coagulase-negative mutant.

CONCLUSION

Inhibition or the absence of staphylothrombin reduced S. aureus virulence in in vitro and in vivo models.

In vivo detection of Staphylococcus aureus endocarditis by targeting pathogen-specific prothrombin activation

Coagulase-positive Staphylococcus aureus (S. aureus) is the major causal pathogen of acute endocarditis, a rapidly progressing, destructive infection of the heart valves. Bacterial colonization occurs at sites of endothelial damage, where (together with fibrin and platelets) it initiates the formation of abnormal growths known as vegetations. Here we report that an engineered analog of prothrombin detected S. aureus in endocarditic vegetations via noninvasive fluorescence or PET imaging. These prothrombin derivatives bound to staphylocoagulase and intercalated into growing bacterial vegetations. We also present evidence for bacterial quorum sensing in the regulation of staphylocoagulase expression by S. aureus. Staphylocoagulase expression was limited to the growing edge of mature vegetations, where it was exposed to the host and co-localized with the imaging probe. When endocarditis was induced with an S. aureus strain with genetic deletion of coagulases, survival of mice improved, highlighting the role of staphylocoagulase as a virulence factor.

NADPH-oxidase but not inducible nitric oxide synthase contributes to resistance in a murine Staphylococcus aureus Newman pneumonia model

Staphylococcus aureus is a pathogen that often causes severe nosocomial infections including pneumonia. The present study was designed to examine innate phagocyte mediated immune mechanisms using a previously described murine S. aureus Newman pneumonia model. We found that BALB/c mice represent a more susceptible mouse strain compared to C57BL/6 mice after intranasal S. aureus Newman challenge. Depletion experiments revealed that neutrophils are a crucial determinant for resistance whereas depletion of alveolar macrophages protected mice to some degree from acute pulmonary S. aureus challenge. C57BL/6 mice lacking the subunit gp91phox of the NADPH-oxidase (gp91phox⁻/⁻ mice) proved to be highly susceptible against the pathogen. In contrast, C57BL/6 inducible nitric oxidase synthase deficient (iNOS⁻/⁻) mice did not differ in their clinical outcome after infection. Neither bone marrow macrophages from iNOS-/- nor from gp91phox⁻/⁻ mice were impaired in controlling intracellular persistence of S. aureus. Our data suggest that neutrophil and NADPH-oxidase mediated mechanisms are essential components in protecting the host against pulmonary S. aureus Newman challenge. On contrary, macrophages as well as NO mediated mechanisms do not seem to play a critical role for resistance in this model.

Influenza virus primes mice for pneumonia from Staphylococcus aureus

Superinfections from Staphylococcus aureus following influenza are an increasing concern. We assessed several laboratory and clinical strains in a mouse coinfection model with influenza virus. A methicillin-resistant USA300 clone and several recent clinical strains from patients with necrotizing pneumonia caused high mortality following influenza virus infection in mice. Both viral and bacterial lung titers were enhanced during coinfections compared with single infections. However, differences in titers did not correspond with differences in disease outcomes in a comparison of superinfections from a highly pathogenic strain with those from a poorly pathogenic strain. These strains did differ, however, in expression of Panton-Valentine leukocidin and in the degree of inflammatory lung damage each engendered. The viral cytotoxin PB1-F2 contributed to the negative outcomes. These data suggest that additional study of specific bacterial virulence factors involved in the pathogenesis of inflammation and lung damage during coinfections is needed.

Encapsulating peritoneal sclerosis: a single-center experience and review of the literature

Encapsulating peritoneal sclerosis (EPS) is a serious and often fatal complication of long-term PD with severe malnutrition and poor prognosis. It causes progressive obstruction and encapsulation of the bowel. This retrospective study reviews our experience and that reviewed in the literature concerning EPS. It refers to a total of 1966 patients treated with chronic PD between 1974 and 2008. Twenty one of them (1.1%) developed EPS, with the incidence increasing with the duration of PD. Mean age of our patients with EPS was 43, ranging from 18 to 71 years, 8 were men and 13 women with a mean body mass index (BMI) of 21.6 kg/m(2). Only one patient had Type II diabetes, 15 patients had glomerular disease, and six of these 15 had an autoimmune disease such as Wegener's granulomatosis and SLE. Thirteen patients developed EPS while on PD, 7 within 2 years after transfer to HD, and only one after renal transplantation. However, 7 patients had a previous renal transplant before returning to PD and subsequently developing EPS. Interestingly, we did not observe more episodes of EPS after transplantation. In the patients who developed EPS, the peritonitis rate over the period of observation was 1/15.6 pt-months and was due to Staphylococcus aureus, coagulase-negative staphylococcus, Pseudomonas and fungi. A history of peritonitis was not a prerequisite for developing EPS, since one patient had no episodes of peritonitis and 4 had just one previous episode. Fifteen patients presented with peritonitis within 4 months before the diagnosis of EPS with particularly virulent micro-organisms such as S. aureus, Candida, Pseudomonas, Corynebacterium, and Peptostreptococcus. Eleven patients were treated with hypertonic dextrose solutions (4.25 g/dl of dextrose) and seven with icodextrin, indirectly suggesting problems with ultrafiltration. Nine of 21 patients were on beta-blockers. The diagnosis of EPS was made either surgically or radiologically with signs of small bowel obstruction in combination with severe malnutrition. Eleven of our patients (52%) had evidence of small bowel obstruction and 14 patients required total parenteral nutrition (TPN). Tamoxifen (10-20 mg daily) was started in 6 patients, 4 of whom are alive and 2 deceased 3 and 5 years after EPS was diagnosed. Of the 12 patients who were not given tamoxifen, 2 are alive and 10 died. No side effects of tamoxifen were reported. Only 7 of our patients (33%) died during the first year after the diagnosis of EPS. Currently, 4 patients are on HD and 3 have had a renal transplant. Six patients of the fourteen who underwent surgery (42.8%) died within the first 6 months after operation and five died after an average of 6.6 years, mostly due to cardiovascular causes, three are still alive. As EPS becomes more prevalent with longer duration of PD, large multicenter prospective studies are needed to establish its incidence and identify risk factors, therapeutic approach, and prognosis.

Dabigatran inhibits Staphylococcus aureus coagulase activity

The ability of Staphylococcus aureus to clot plasma through conformational activation of prothrombin by staphylocoagulase is used to distinguish S. aureus from coagulase-negative staphylococci. We show that while the direct thrombin inhibitor dabigatran inhibits staphylocoagulase activity, the clinical use of dabigatran etexilate is not expected to interfere with direct tube coagulase testing.

Involvement of endotoxin in the mortality of mice with gut-derived sepsis due to methicillin-resistant Staphylococcus aureus

MRSA causes a wide diversity of diseases, ranging from benign skin infections to life-threatening diseases, such as sepsis. However, there have been few reports of the pathophysiology and mechanisms of sepsis resulting from the gut-derived origin of MRSA. Therefore, we established a murine model of gut-derived sepsis with MRSA and factors of MRSA sepsis that cause deterioration. We separated mice into four groups according to antibiotic treatment as follows: (i) ABPC 40 mg/kg; (ii) CAZ 80 mg/kg; (iii) CAZ 80 mg/kg + endotoxin 10 microg/mouse; and (iv) saline-treated control groups. Gut-derived sepsis was induced by i.p. injection of cyclophosphamide after colonization of MRSA strain 334 in the intestine. After the induction of sepsis, significantly more CAZ-treated mice survived compared with ABPC-treated and control groups. MRSA were detected in the blood and liver among all groups. Endotoxin levels were significantly lower in the CAZ-treated group compared to other groups. Inflammatory cytokine levels in the serum were lower in the CAZ-treated group compared to other groups. Fecal culture showed a lower level of colonization of E. coli in the CAZ-treated group compared to other groups. In conclusion, we found that CAZ-treatment ameliorates infection and suppresses endotoxin level by the elimination of E. coli from the intestinal tract of mice. However, giving endotoxin in the CAZ-treated group increased mortality to almost the same level as in the ABPC-treated group. These results suggest endotoxin released from resident E. coli in the intestine is involved in clinical deterioration resulting from gut-derived MRSA sepsis.

Global proteome analysis of Leptospira interrogans

Comparative global proteome analyses were performed on Leptospira interrogans serovar Copenhageni grown under conventional in vitro conditions and those mimicking in vivo conditions (iron limitation and serum presence). Proteomic analyses were conducted using iTRAQ and LC-ESI-tandem mass spectrometry complemented with two-dimensional gel electrophoresis and MALDI-TOF mass spectrometry. A total of 563 proteins were identified in this study. Altered expression of 65 proteins, including upregulation of the L. interrogans virulence factor Loa22 and 5 novel proteins with homology to virulence factors found in other pathogens, was observed between the comparative conditions. Immunoblot analyses confirmed upregulation of 5 of the known or putative virulence factors in L. interrogans exposed to the in vivo-like environmental conditions. Further, ELISA analyses using serum from patients with leptospirosis and immunofluorescence studies performed on liver sections derived from L. interrogans-infected hamsters verified expression of all but one of the identified proteins during infection. These studies, which represent the first documented comparative global proteome analysis of Leptospira, demonstrated proteome alterations under conditions that mimic in vivo infection and allowed for the identification of novel putative L. interrogans virulence factors.

The L. interrogans proteome was analyzed using iTRAQ and 2DGE. These analyses identified 563 proteins and altered expression of 65 proteins upon growth of L. interrogans under in vivo-like conditions, including upregulation of the L. interrogans virulence factor Loa22, a putative lipoprotein with primary amino acid sequence similarity to the outer surface protein ErpY of B. burgdorferi, and 4 additional proteins with homology to virulence factors found in other pathogens.

The effect of subminimal inhibitory concentrations of antibiotics on virulence factors expressed by Staphylococcus aureus biofilms

AIMS

The effect of subminimal inhibitory concentrations (sub-MICs) of cefalexin, ciprofloxacin and roxithromycin was investigated on some virulence factors [e.g. coagulase, Toxic Shock Syndrome Toxin 1 (TSST-1) and biofilm formation] expressed by Staphylococcus aureus biofilms.

METHODS AND RESULTS

Biofilms were grown with and without the presence of 1/16 MIC of antibiotics on Sorbarod filters. Eluate supernatants were collected, and coagulase and TSST-1 production were evaluated. Coagulase production was reduced in eluates exposed to roxithromycin when compared to control, while TSST-1 production was reduced in biofilms exposed to cefalexin and to a lesser extent, ciprofloxacin. In addition, the ability of Staph. aureus to produce biofilm in microtitre plates in the presence of sub-MIC antibiotics indicated that cefalexin induced biofilm formation at a wide range of sub-MICs. TSST-1 produced from the challenged and control biofilms was purified, and its proliferative activity was studied on single cell suspension of mouse splenocytes using MTS/PMS assay. No significant difference in the activity between the treated toxin and the control has been observed.

CONCLUSIONS

Antibiotics at sub-MIC levels interfere with bacterial biofilm virulence expression depending on the type and concentration of antibiotic used.

SIGNIFICANCE AND IMPACT OF THE STUDY

The establishment of sub-MICs of antibiotics in clinical situations may result in altered virulence states in pathogenic bacteria.

Potency of SMP-601, a novel carbapenem, in hematogenous murine bronchopneumonia caused by methicillin-resistant and vancomycin-intermediate Staphylococcus aureus

We compared the potency of SMP-601, a novel carbapenem, with that of vancomycin in a murine model of hematogenous bronchopneumonia infection caused by methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-intermediate S. aureus (VISA). The MICs of SMP-601 and vancomycin against MRSA were 2 and 1 mug/ml, respectively, while those against VISA were 2 and 8 mug/ml, respectively. Treatment with SMP-601 resulted in a significant decrease in the number of viable bacteria in the MRSA infection model (control, 100 mg/kg vancomycin, and 100 mg/kg SMP-601, 8.42 +/- 0.50, 5.29 +/- 0.71, and 5.50 +/- 0.58 log CFU/lung, respectively,) and in the VISA infection model (control, 100 mg/kg vancomycin, and 100 mg/kg SMP-601, 9.64 +/- 0.63, 8.72 +/- 0.45, 7.42 +/- 0.14 log CFU/lung) (mean +/- standard error of the mean). The survival rate in the VISA infection model treated with SMP-601 (70%) was significantly higher than those in the other two groups (20% for vancomycin and 0% for control; P < 0.05). Histopathological examination revealed that inflammatory changes in the SMP-601-treated group were less marked than in the other two groups. The results of pharmacokinetic-pharmacodynamic analysis supported the results of the bacteriological, histopathological and survival studies. Our results demonstrate the potency of SMP-601 against MRSA and VISA in murine hematogenous pulmonary infection.

The anti-inflammatory activities of Staphylococcus aureus

Staphylococcus aureus is a versatile and harmful pathogen in both hospital- and community-associated infections that range from superficial to systemic infections. S. aureus engages a multitude of mechanisms to subvert the innate immune response of the host, including inhibition of complement activation and neutralization of anti-microbial peptides. In addition, inflammatory cell and phagocyte recruitment is an integral part of the innate defense to staphylococcal infection and comprises a well-coordinated multi-step cascade of adhesive events. Recent and rapidly growing experimental evidence indicates the existence of a machinery of anti-adhesive and anti-chemotactic moieties of S. aureus that allow the bacterium to interfere with specific adhesive steps of the homing mechanism of leukocytes. Understanding the functions of these S. aureus-derived anti-inflammatory agents could also provide the platform for designing new therapies in several inflammatory and autoimmune diseases.

Molecular analysis of the thymidine-auxotrophic small colony variant phenotype of Staphylococcus aureus

Thymidine-auxotrophic small colony variants (SCVs) of Staphylococcus aureus are frequently isolated from the chronically infected airways of patients suffering from cystic fibrosis. To date, little is known regarding the molecular mechanisms leading to the formation of this special phenotype, but the auxotrophism for thymidine suggests that impaired thymidine metabolism might play a major role. Sequence analysis of the thymidylate synthase-encoding thyA gene of six clinical thymidine-auxotrophic S. aureus SCVs revealed that all isolates had mutations within thyA. In five isolates the function of the thymidylate synthase was definitely impaired: three of them showed a truncation of the thyA coding sequence by nonsense or frame-shift mutations, in one further isolate the active site of the enzyme was affected by an internal 12-bp deletion, and another isolate had a 173-bp deletion spanning the 5'-terminal region of thyA and the preceding DNA sequence. The sixth isolate showed two amino acid substitutions within the thyA gene product. To confirm the importance of impaired thymidylate synthase synthesis or activity for the formation of the thymidine-auxotrophic SCV phenotype, we constructed a thyA knock-out mutant of a wild-type S. aureus strain. This mutant showed all characteristics of clinical SCVs, such as slow growth, decreased pigment production, reduced hemolytic activity, auxotrophism for thymidine, resistance to trimethoprim/sulfamethoxazol, and reduced plasma coagulase activity. Complementation of the thyA knock-out mutant with intact thyA in trans nearly restored the normal phenotype. In conclusion, these data confirm at the molecular level that impaired thymidylate synthase function is causative for the formation of the thymidine-auxotrophic SCV phenotype in S. aureus.

Surface proteins and exotoxins are required for the pathogenesis of Staphylococcus aureus pneumonia

A model of Staphylococcus aureus-induced pneumonia in adult, immunocompetent C57BL/6J mice is described. This model closely mimics the clinical and pathological features of pneumonia in human patients. Using this system, we defined a role for S. aureus strain Newman surface proteins and secreted exotoxins in pneumonia-related mortality.

Potency of DX-619, a novel des-F(6)-quinolone, in haematogenous murine bronchopneumonia caused by methicillin-resistant and vancomycin-intermediate Staphylococcus aureus

In this study, the potency of DX-619, a novel des-fluoro(6)-quinolone agent, was compared with that of vancomycin (VCM) in a murine model of haematogenous bronchopneumonia infection caused by methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-intermediate S. aureus (VISA). The minimum inhibitory concentrations (MICs) of DX-619 and VCM against MRSA were 0.03 microg/mL and 1.0 microg/mL, respectively, whilst the MICs against VISA were 0.125 microg/mL and 8.0 microg/mL, respectively. Treatment with DX-619 resulted in a significant decrease in the number of viable bacteria in the MRSA infection model (mean+/-standard error of the mean for control, VCM and DX-619 groups: 7.97+/-0.32, 7.19+/-0.33 and 2.91+/-0.60 log(10) colony-forming units/lung, respectively). For infection with VISA, mice were pre-treated with cyclophosphamide. The survival rate of mice treated with DX-619 (90% survival) was significantly higher than survival rates in the other two groups (45% both for VCM and control groups; P<0.05). Histopathological examination revealed that inflammatory changes in the DX-619-treated group were less marked than in the other two groups. The parameters in lung tissue for the area under the concentration-time curve/MIC ratio both for MRSA and VISA were higher in the DX-619 group than in the VCM group. Our results emphasise the potency of DX-619 against MRSA and VISA murine haematogenous pulmonary infection.

The neutralizing effects of hyperimmune antibodies against extracellular fibrinogen-binding protein, Efb, from Staphylococcus aureus

Staphylococcus aureus is a significant cause of acute and chronic infection and boasts a diverse array of virulence factors. S. aureus produces and secretes a protein, extracellular fibrinogen (Fg)-binding protein (Efb), which contributes to virulence in wound infection. Efb binds to both Fg and platelets and inhibits platelet function in vitro and in vivo. In this study, we have characterized the antibody response against Efb. Antibodies generated in response to immunization with Efb can neutralize the biological effects of Efb. Hyperimmune sheep immunoglobulin (Ig)G against Efb blocked the binding of Efb to Fg and prevented Efb-mediated inhibition of platelet aggregation. Furthermore, these antibodies cross-reacted with coagulase and blocked coagulase activity in plasma. Immunization of mice with Efb resulted in the generation of high titre specific antibodies. When subjected to a foreign-body-associated wound infection, the vaccinated animals developed significantly less severe wound infection than the unvaccinated controls. Also, human IgG against Efb was prepared from commercial IgG pools; however, the monospecific human anti-Efb that was enriched was unable to neutralize Efb. We conclude that immunization with Efb is required in order to generate a protective antibody response to Efb from S. aureus.

The extracellular adherence protein (Eap) of Staphylococcus aureus inhibits wound healing by interfering with host defense and repair mechanisms

Staphylococcus aureus is a major human pathogen interfering with host-cell functions. Impaired wound healing is often observed in S aureus-infected wounds, yet, the underlying mechanisms are poorly defined. Here, we identify the extracellular adherence protein (Eap) of S aureus to be responsible for impaired wound healing. In a mouse wound-healing model wound closure was inhibited in the presence of wild-type S aureus and this effect was reversible when the wounds were incubated with an isogenic Eap-deficient strain. Isolated Eap also delayed wound closure. In the presence of Eap, recruitment of inflammatory cells to the wound site as well as neovascularization of the wound were prevented. In vitro, Eap significantly reduced intercellular adhesion molecule 1 (ICAM-1)-dependent leukocyte-endothelial interactions and diminished the consequent activation of the proinflammatory transcription factor nuclear factor kappaB (NFkappaB) in leukocytes associated with a decrease in expression of tissue factor. Moreover, Eap blocked alphav-integrin-mediated endothelial-cell migration and capillary tube formation, and neovascularization in matrigels in vivo. Collectively, the potent anti-inflammatory and antiangiogenic properties of Eap provide an underlying mechanism that may explain the impaired wound healing in S aureus-infected wounds. Eap may also serve as a lead compound for new anti-inflammatory and antiangiogenic therapies in several pathologies.

Effects of short interfering RNA against methicillin-resistant Staphylococcus aureus coagulase in vitro and in vivo

OBJECTIVES

The emergence of antibiotic-resistant bacteria such as Staphylococcus aureus calls for inventive research and development strategies. Inhibition of bacterial pathogenesis may be a promising therapeutic approach in this regard. The gene-silencing effect of short interfering RNA (siRNA) is useful for this strategy. We investigated the efficacy of siRNA on the expression of coagulase because it is the one of the most important enzymes in the pathogenesis of methicillin-resistant S. aureus (MRSA) infection.

METHODS

We designed and synthesized 21 bp siRNA duplexes against staphylococcal coagulase. RT-PCR was performed to determine whether the siRNAs inhibit the expression of the coagulase mRNA and radio-labelled siRNA was used to confirm transfection to bacteria in vitro. The efficacy of siRNA was determined in a murine model of haematogenous pulmonary infection.

RESULTS

RT-PCR showed that siRNAs significantly inhibited the expression of the coagulase mRNA. The coagulase titres in the siRNA and control groups were 8 and 32, respectively. Measurement of incorporated radioactivity indicated that the siRNAs were delivered into the bacteria. In the murine infection model, in control and siRNA groups, 7.64 +/- 0.42 and 6.29 +/- 0.23 log cfu/mL (mean +/- SEM) MRSA were detected, respectively, showing that there was a significant decrease in the number of viable bacteria in the siRNA group (P < 0.05).

CONCLUSIONS

The results show that siRNA inhibited both mRNA expression and the activity of MRSA coagulase in vitro. The in vivo results revealed that the siRNA was effective in reducing the bacterial load in a murine model of haematogenous pulmonary infection. Targeting of coagulase with siRNA appears to be a novel strategy for treating MRSA infections.

Novel fluorescent prothrombin analogs as probes of staphylocoagulase-prothrombin interactions

Staphylocoagulase (SC) is a potent nonproteolytic prothrombin (ProT) activator and the prototype of a newly established zymogen activator and adhesion protein family. The staphylocoagulase fragment containing residues 1-325 (SC-(1-325)) represents a new type of nonproteolytic activator with a unique fold consisting of two three-helix bundle domains. The N-terminal, domain 1 of SC (D1, residues 1-146) interacts with the 148 loop of thrombin and prethrombin 2 and the south rim of the catalytic site, whereas domain 2 of SC (D2, residues 147-325) occupies (pro)exosite I, the fibrinogen (Fbg) recognition exosite. Reversible conformational activation of ProT by SC-(1-325) was used to create novel analogs of ProT covalently labeled at the catalytic site with fluorescence probes. Analogs selected from screening 10 such derivatives were used to characterize quantitatively equilibrium binding of SC-(1-325) to ProT, competitive binding with native ProT, and SC domain interactions. The results support the conclusion that SC-(1-325) binds to a single site on fluorescein-labeled and native ProT with indistinguishable dissociation constants of 17-72 pM. The results obtained for isolated SC domains indicate that D2 binds ProT with approximately 130-fold greater affinity than D1, yet D1 binding accounts for the majority of the fluorescence enhancement that accompanies SC-(1-325) binding. The SC-(1-325).(pro)thrombin complexes and free thrombin showed little difference in substrate specificity for tripeptide substrates or with their natural substrate, Fbg. Lack of a significant effect of blockage of (pro)exosite I of (pro)thrombin by SC-(1-325) on Fbg cleavage indicates that a new Fbg substrate recognition exosite is expressed on the SC-(1-325).(pro)thrombin complexes. Our results provide new insight into the mechanism that mediates zymogen activation by this prototypical bacterial activator.

The staphylocoagulase family of zymogen activator and adhesion proteins

Staphylocoagulase (SC) secreted by Staphylococcus aureus is a potent non-proteolytic activator of the blood coagulation zymogen prothrombin and the prototype of a newly established zymogen activator and adhesion protein (ZAAP) family. The conformationally activated SC.prothrombin complex specifically cleaves fibrinogen to fibrin, which propagates the growth of bacteria-fibrin-platelet vegetations in acute bacterial endocarditis. Our recent 2.2 A X-ray crystal structures of an active SC fragment [SC(1-325)] bound to the prothrombin zymogen catalytic domain, prethrombin 2, demonstrated that SC(1-325) represents a new type of non-proteolytic activator with a unique fold. The observed insertion of the SC(1-325) N-terminus into the 'Ile 16' cleft of prethrombin 2, which triggers the activating conformational change, provided the first unambiguous structural evidence for the 'molecular sexuality' mechanism of non-proteolytic zymogen activation. Based on the SC(1-325) fold, a new family of bifunctional zymogen activator and adhesion proteins was identified that possess N-terminal domains homologous to SC(1-325) and C-terminal domains that mediate adhesion to plasma or extracellular matrix proteins. Further investigation of the ZAAP family may lead to new insights into the mechanisms of bacterial factors that hijack zymogens of the human blood coagulation and fibrinolytic systems to promote and disseminate endocarditis and other infectious diseases.

Efficacy of Quinupristin-Dalfopristin against Methicillin-Resistant Staphylococcus aureus and Vancomycin-Insensitive S. aureus in a Model of Hematogenous Pulmonary Infection

BACKGROUND

Quinupristin-dalfopristin (Q-D) is a mixture of quinupristin and dalfopristin, which are semisynthetic antibiotics of streptogramin groups B and A, respectively.

METHODS

We compared the effect of Q-D to that of vancomycin (VCM) in murine models of hematogenous pulmonary infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and VCM-insensitive S. aureus (VISA).

RESULTS

Treatment with Q-D resulted in a significant decrease in the number of viable bacteria in the lungs of mice in an MRSA infection model [Q-D 100 mg/kg, Q-D 10 mg/kg, VCM and control (mean +/- SEM): 2.99 +/- 0.44, 6.38 +/- 0.32, 5.75 +/- 0.43 and 8.40 +/- 0.14 log10 CFU/lung, respectively]. Compared with VCM, high-dose Q-D significantly reduced the number of bacteria detected in the VISA hematogenous infection model [Q-D 100 mg/kg, Q-D 10 mg/kg, VCM and control (mean +/- SEM): 5.17 +/- 0.52, 7.03 +/- 0.11, 7.10 +/- 0.49 and 7.18 +/- 0.36 log10 CFU/lung, respectively]. Histopathological examination confirmed the effect of Q-D.

CONCLUSION

Our results suggest that Q-D is potent and effective in the treatment of MRSA and VISA hematogenous pulmonary infections.

Glycopeptide resistance in Staphylococcus aureus: is it a real threat?

Following the discovery in 1992 that resistance to vancomycin could be transferred in vitro from a strain of Staphylococcus haemolyticus to Staphylococcus aureus, the threat that a similar event could happen in vivo has existed. In 1996, the threat became a reality in Japan followed by reports of low-level heteroresistant S. aureus from elsewhere in the world. However, the threat has not gone away; indeed it has become more intimidating within the past 2 years with the isolation of higher-level resistance to vancomycin transferred on a plasmid from Enterococcus faecalis. The mechanisms of resistance are different in each of the types of S. aureus with reduced susceptibility to the glycopeptides: in one hetero-vancomycin intermediate-susceptible S. aureus (hVISA) and vancomycin intermediate-susceptible S. aureus (VISA), cell wall biosynthesis is altered, hindering glycopeptide reaching its target, and in the other vancomycin-resistant S. aureus (VRSA) the target is altered. This review attempts to place into context the threat posed to patients by the appearance of strains of S. aureus more resistant to one of the key therapeutic agents used in our hospitals. It will do so by raising a number of important questions followed by the presentation of experimental evidence that may or may not provide answers that heighten or lower the threat.