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.

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.

Targeting staphylocoagulase with isoquercitrin protects mice from Staphylococcus aureus-induced pneumonia.

Staphylocoagulase (Coa) is a virulence factor of Staphylococcus aureus (S. aureus) that promotes blood coagulation by activating prothrombin to convert fibrinogen to fibrin. Coa plays a crucial role in disease pathogenesis and is a promising target for the treatment of S. aureus infections. Here, we identified that isoquercitrin, a natural flavonol compound, can markedly reduce the activity of Coa at concentrations that have no effect on bacterial growth. Mechanistic studies employing molecular dynamics simulation revealed that isoquercitrin binds to Coa by interacting with Asp-181 and Tyr-188, thereby affecting the binding of Coa to prothrombin. Importantly, in vivo studies showed that isoquercitrin treatment significantly reduced the bacterial burden, pathological damage, and inflammation of lung tissue and improved the percentage of survival of mice infected with S. aureus Newman strain. These data suggest that isoquercitrin is a promising inhibitor of Coa that can be used for the development of therapeutic drugs to combat S. aureus infections.Key Points• Staphylocoagulase plays a key role in the pathogenesis of S. aureus infection.• We identified that isoquercitrin is a direct inhibitor of staphylocoagulase.• Isoquercitrin treatment can significantly attenuate S. aureus virulence in vivo.

Inhibitory effects of Inula britannica extract fermented by Lactobacillus plantarum KCCM 11613P on coagulase activity and growth of Staphylococcus aureus including methicillin-resistant strains.

The aim of this study was to evaluate the antimicrobial efficacy of fermented Inula britannica extract (FIBE) against Staphylococcus aureus strains including methicillin-resistant S. aureus (MRSA). I. britannica extract was fermented by Lactobacillus plantarum KCCM 11613P, and the pathogenicity of S. aureus strains was determined via assessment of coagulase, DNase, and hemolytic activities. Epicatechin concentration increased from 4.38 to 6.05 µg/mg during fermentation (p < 0.01). FIBE treatment inhibited coagulase release from S. aureus to levels below the inhibitory concentration. FIBE promoted the release of intracellular nucleic acids and N-phenyl-1-naphthylamine absorption. In three S. aureus strains, damaged cells exhibited 21.58, 16.79, and 17.65% decreases in membrane potential induced by cell membrane depolarization, respectively (p < 0.05). Upon FIBE treatment in culture, the minimum inhibitory concentration of FIBE exerted a bacteriostatic effect. In conclusion, FIBE possesses antimicrobial properties, including inhibition of virulence factors, damage to cell membranes, and inhibition of bacterial growth. PRACTICAL APPLICATIONS: Methicillin-resistant Staphylococcus aureus (MRSA) is a serious concern in hospitals because of its known antibiotic resistance. Vancomycin and tigecycline are used for treating MRSA, but the appearance of vancomycin-intermediate and multidrug-resistant strains of these bacteria has created a demand for new antimicrobial agents. This study demonstrates the effective application of Inula britannica and fermentation technology for developing natural antimicrobial agents against methicillin-resistant Staphylococcus aureus.

Quercetin protects rats from catheter-related Staphylococcus aureus infections by inhibiting coagulase activity.

Coagulase (Coa) activity is essential for the virulence of Staphylococcus aureus (S aureus), one of the most important pathogenic bacteria leading to catheter-related bloodstream infections (CRBSI). We have demonstrated that the mutation of coagulase improved outcomes in disease models of S aureus CRBSI, suggesting that targeting Coa may represent a novel antiinfective strategy for CRBSI. Here, we found that quercetin, a natural compound that does not affect S aureus viability, could inhibit Coa activity. Chemical biological analysis revealed that the direct engagement of quercetin with the active site (residues Tyr187, Leu221 and His228) of Coa inhibited its activity. Furthermore, treatment with quercetin reduced the retention of bacteria on catheter surfaces, decreased the bacterial load in the kidneys and alleviated kidney abscesses in vivo. These data suggest that antiinfective therapy targeting Coa with quercetin may represent a novel strategy and provide a new leading compound with which to combat bacterial infections.

Targeting Coagulase Activity in Staphylococcus aureus Bacteraemia: A Randomized Controlled Single-Centre Trial of Staphylothrombin Inhibition.

BACKGROUND: Staphylococcus aureus (S. aureus) bacteraemia is frequent and carries a high morbidity and mortality. Coagulases secreted by S. aureus initiate blood coagulation by directly activating prothrombin. This pathogen-activated coagulation is insensitive to most antithrombotic drugs, with the exception of small molecule direct thrombin inhibitors (DTIs). DTIs inhibit the coagulase-prothrombin complex, or staphylothrombin, and improve outcome in preclinical models of S. aureus infection. OBJECTIVE: A single-centre, randomized, controlled feasibility and safety trial of staphylothrombin inhibition with DTIs in patients with S. aureus bacteraemia. PATIENTS AND METHODS: Consecutive eligible adult patients with S. aureus positive blood cultures in the University Hospitals Leuven (Belgium) were randomized 1:1 to DTI (oral dabigatran 110 mg twice daily or intravenous argatroban according to activated partial thromboplastin time [aPTT]) for 7 to 10 days, or subcutaneous enoxaparin 40 mg once daily. Primary outcomes were feasibility and safety of DTI in patients with S. aureus bacteraemia. Secondary outcomes include D-dimer evolution (day 0-4) as marker of coagulation activation; inflammatory and microbiological parameters; and clinical outcomes including metastatic infections. RESULTS: Thirty-one percent (94/303) of screened patients were enrolled. Dabigatran plasma levels inhibited staphylothrombin. Clinically relevant bleeding (5/47 vs. 5/47) and thrombotic (7/47 vs. 7/47) complications were similar in both groups. Coagulase inhibition with DTIs was associated with a trend towards faster D-dimer decrease at day 4 (-662 ± 249 ng/mL vs. -40 ± 213 ng/mL for DTI-treated patients vs. control; p = 0.06) and a numerically lower number of persistently positive blood cultures. No differences in inflammatory parameters or other clinical outcomes were observed. CONCLUSION: Targeting staphylothrombin with DTIs is feasible in a subset of S. aureus bacteraemic patients, with comparable safety to standard thromboprophylaxis. In future studies of staphylothrombin inhibition, feasibility can be further improved by rapid diagnostics and by strategies without concomitant anticoagulant effect.

Coagulase Activity by Staphylococcus aureus: A Potential Target for Therapy?

Staphylococcus aureus is a leading cause of skin and soft tissue infections, foreign body infections, and infective endocarditis. In case of endovascular infection with S. aureus, higher rates of cardiac valve destruction, embolic complications, severe sepsis, and death occur. The unique capacity of S. aureus to induce clotting has been known for over a century; however, its role in virulence has long been controversial. S. aureus secretes two coagulases, staphylocoagulase and von Willebrand factor binding protein that both activate prothrombin to generate fibrin. A better understanding of the molecular mechanisms as well as the new strategies to target the coagulases have highlighted their importance in S. aureus virulence. Coagulase activity is essential for the formation of S. aureus-fibrin-platelet microaggregates and for the homing of S. aureus to the vascular wall under flow. Absence or inhibition of S. aureus coagulase activity improved outcome in disease models of skin infection, sepsis, catheter infection, and endocarditis. Here, we review how the manipulation of the host's hemostatic system contributes to the disease-causing potential of S. aureus and discuss the S. aureus coagulases as promising targets for novel therapeutic strategies.

Effects of Tamarind (Tamarindus indicus Linn) seed extract on Russell's viper (Daboia russelli siamensis) venom.

Snake bite has been regarded as an important health problem in Myanmar since early 1960's. In the recent years, there has been growing interest in alternative therapies and therapeutic use of natural products, especially those derive from plants. In Myanmar and Indian traditional medicine, various plants have used as a remedy for treating snake bite. The present study was carried out to evaluate the effects of alcohol extract of Tamarind (Tamarindus indica Linn.) seed on some biologic properties of Russell's viper (Daboia russelli siamensis) venom (RVV). The Phospholipase A2 (PLA2) enzyme, coagulase enzyme and caseinolytic enzyme activities of Russell's viper venom (RVV) were reduced when mixed and incubated with the extract. When the RVV and the different amount of extracts were preincubated and injected intramuscularly into mice, all of them survived, but all the mice in the control group died. On the other hand, when RVV were injected first followed by the extract into mice, all of them died. If the extract was injected near the site where Russell's viper venom was injected, all the mice survived for more than 24 hours and the survival time prolonged but they all died within 96 hours. In conclusion, according to the results obtained, the extract neutralizes some biologic properties of the Russell's viper venom and prolonged the survival time if the extract was injected near the site where the Russell's viper venom was injected.

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.

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.

Subinhibitory concentrations of telithromycin, clarithromycin and azithromycin reduce methicillin-resistant Staphylococcus aureus coagulase in vitro and in vivo.

BACKGROUND: Subinhibitory levels of clarithromycin and azithromycin have been shown to reduce the activity of bacterial virulence factors, but few studies have examined the effects of subinhibitory levels of telithromycin. Here, we examined the effects of telithromycin, clarithromycin and azithromycin on methicillin-resistant Staphylococcus aureus (MRSA) coagulase in vitro. We also examined the effects of these antibiotics on bacterial survival in a murine model of pulmonary infection, in which the number of bacteria in the lung correlates with the coagulase titre. METHODS: The coagulase titre in MRSA strain NUMR101, a clinical isolate, was measured after a 16 h treatment with telithromycin, clarithromycin or azithromycin at the MIC (512 mg/L) and 1/2, 1/4, 1/8 and 1/16 of the MIC. In addition, we examined the effect of these drugs in a murine model of pulmonary infection induced by the intravenous injection of S. aureus enmeshed in agar beads. Treatment was started 1 day before infection and mice were treated once a day for 7 days by oral administration of 10 or 100 mg/kg telithromycin, clarithromycin or azithromycin, and the number of viable bacteria in the lungs was counted 24 h after the injection of the bacteria. RESULTS: The coagulase titres in mice treated with 1/8 of the MIC of telithromycin, clarithromycin and azithromycin and in the control were 8, 4, 8 and 32, respectively. In the mouse model of infection, the log cfu/lung (mean +/- SEM; n = 5 or 6) were 6.62 +/- 0.81, 4.79 +/- 0.41, 6.15 +/- 0.38 and 8.41 +/- 0.30 for mice treated with 100 mg/kg/day of telithromycin, clarithromycin and azithromycin and for controls, respectively (P < 0.05 for all groups versus control). CONCLUSIONS: Subinhibitory concentrations of telithromycin inhibit MRSA coagulase in vitro. In addition, the in vivo results indicate that pre-treatment with telithromycin, clarithromycin or azithromycin can reduce the bacterial load in a murine model of pulmonary infection.

Capsular polysaccharide masks clumping factor A-mediated adherence of Staphylococcus aureus to fibrinogen and platelets.

BACKGROUND: Clumping factor A (ClfA) is a Staphylococcus aureus cell wall-associated adhesin that mediates staphylococcal binding to fibrinogen and platelets. Our goals were to determine whether expression of capsular polysaccharide (CP) affected ClfA-mediated adherence of S. aureus and to assess whether the length of the ClfA repeat region influenced this interaction. METHODS: ClfA constructs with repeat regions of different lengths were introduced into isogenic S. aureus strains that expressed CP5, CP8, or no CP. S. aureus binding to fibrinogen was assessed in rabbit plasma and on fibrinogen-coated microtiter plates. Adherence of S. aureus strains to platelets was evaluated by flow cytometry and confocal microscopy. RESULTS: As the length of the ClfA repeat region increased, binding of acapsular S. aureus to fibrinogen-coated microtiter plates was enhanced. By contrast, encapsulated S. aureus expressing the full-length ClfA were poorly adherent. The acapsular S. aureus mutant strain showed a 2-fold increase in platelet binding, compared with the isogenic encapsulated strains. By contrast, platelet aggregation was unaffected by CP production. CONCLUSION: CP expression inhibits S. aureus ClfA-mediated binding to fibrinogen and platelets, and a full-length repeat region cannot overcome this inhibition. These findings have important implications for vaccine development, given that CP may mask surface adhesins.

The role of Staphylococcus aureus surface protein SasG in adherence and biofilm formation.

Staphylococcus aureus colonizes the moist squamous epithelium of the anterior nares. One of the adhesins likely to be responsible is the S. aureus surface protein G (SasG), which has sequence similarity with the proteins Pls (plasmin sensitive) of S. aureus and Aap (accumulation associated protein) of Staphylococcus epidermidis. Expression of SasG by a laboratory strain of S. aureus could not be detected by Western immunoblotting. To enable investigation of SasG, the gene was cloned into two expression vectors, the IPTG-inducible pMUTIN4 and the tetracycline-inducible pALC2073, and introduced into S. aureus. Expression of SasG masked the ability of exponentially grown S. aureus cells expressing protein A (Spa), clumping factor B (ClfB) and the fibronectin binding proteins A and B (FnBPA and FnBPB) to bind to IgG, cytokeratin 10 and fibronectin, respectively. SasG also masked binding to fibrinogen mediated by both ClfB and the FnBPs. Western immunoblotting showed no reduction in expression of the blocked adhesins following induction of SasG. SasG size variants with eight, six or five B repeats masked binding to the ligands, whereas variants with four, two or one repeats had no effect. SasG-expressing strains formed peritrichous fibrils (53.47+/-2.51 nm long) of varying density on the cell wall, which were labelled by immunogold negative staining with anti-SasG antibodies. SasG-expressing strains of S. aureus also formed biofilm independently of the polysaccharide intercellular adhesin (PIA). SasG variants with eight, six and five repeats formed biofilm, whereas variants with four, two or one repeats did not. It was concluded that the fibrillar nature of SasG explains its ability to mask binding of S. aureus microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) to their ligands and to promote formation of biofilm. In addition, the strong adhesion of SasG to desquamated nasal epithelial cells likely compensates for its blocking of the binding of S. aureus ClfB to cytokeratin 10, which is important in adhesion to squames by cells lacking SasG. Several clinical isolates expressed SasG at levels similar to those of SH1000 sasG : : pMUTIN4, indicating that the properties described in the laboratory strain SH1000 may be relevant in vivo.

Study of developed resistance due to antibiotic treatment of coagulase-negative Staphylococci.

Coagulase-negative Staphylococci (CoNS) are a major cause of postoperative infections. These infections are often associated with foreign material implants and/or a compromised immune system in the patient. Multiresistant strains are increasingly common in the hospital environment and there is concern that the infections will become difficult or impossible to treat. This report is based on a study of 75 patients, with postoperative infections caused by CoNS after thoracic surgery. All patients were treated with surgical revision and antibiotic therapy. One or more bacterial cultures were made in each case, and the resistance pattern of the CoNS found was determined. The goal of the study was to evaluate possible relationships between antibiotic therapy and the appearance of resistance to antibiotics in CoNS found. To describe this relationship, three models were constructed and analyzed by multiple logistic regression. The results indicate an increased resistance to beta-lactam antibiotics and clindamycin after the use of cephalosporins. Also, the use of vancomycin or vancomycin in combination with rifampicin or fusidic acid increases the risk for development of resistance to beta-lactam antibiotics, ciprofloxacin, fusidic acid, clindamycin, netilmycin, and rifampicin. The hypothesis that a combination of antibiotics will curtail the development of resistance was not supported in this study.

Effects of Helichrysum italicum extract on growth and enzymatic activity of Staphylococcus aureus.

Helichrysum italicum G. Don (Compositae) is a shrub commonly found in dry, sandy and stony areas of Mediterranean regions. This plant is known for its anti-inflammatory, anti-allergic and antimicrobial activity. The aim of this study was to evaluate the effect of the diethyl ether extract on growth of Staphylococcus aureus (ATCC 6538P, MRSA and MSSA isolates) and the influence of subminimum inhibitory concentrations (subMICs) on some enzymes which are considered virulence factors. The results indicate that the H. italicum extract had an inhibitory effect on S. aureus strains reducing both their growth and some of the enzymes such as coagulase, DNAse, thermonuclease and lipase. Helichrysum italicum extract could be a novel antimicrobial agent, less toxic to human skin and tissues, worthy of further studies.

[The ability of low-molecular heparin (Fraxiparin) to overcome the action of exogenous coagulases--a fundamental difference from nonfractionated heparin]. / Sposobnost' nizkomolekuliarnogo geparina (fraksiparina) preodolevat' deistvie ékzogennykh koagulaz--fundamental'noe otlichie ot nefraktsionirovannogo geparina.

A new previously unknown activity of the low molecular-weight heparin Fraxiparin (Sanofi) has been discovered. This is its ability to reduce the plasma clotting action of snake venom coagulases at final concentration of more than 12.5 anti-Xa U/ml, while the unfractionated heparin does not possess this property. The experiments demonstrated that Fraxiparin the action of Echis carinatus prothrombin-activating venom to a greater degree and Agkistrodon halys halys thrombin-like coagulase to a lesser degree. Unlike the unfractionated heparin, Fraxiparan also prevents the death of white rats from acute toxic hemocoagulant shock caused by the intravenous injection of DL100 Echis carinatus venom.

Effect of sub-inhibitory concentrations of antibiotics on the virulence of Staphylococcus aureus.

The production of virulence factors by various bacteria can be influenced by sub-inhibitory concentrations of antibiotics. The effect of six antibiotics on the production of representative extracellular enzymes and toxins produced by Staphylococcus aureus was investigated. The production of the virulence determinants coagulase, protein A, alpha and delta haemolysin was monitored in the presence of ciprofloxacin, enoxacin, chloramphenicol, gentamicin, tetracycline and methicillin. The protein synthesis inhibitors reduced the production of coagulase and protein A, and almost completely inhibited the production of the haemolysins. Haemolysin production was also reduced by ciprofloxacin and enoxacin, but these antibiotics had little effect on the production of coagulase and protein A. Methicillin stimulated the production of alpha and delta haemolysins but had no effect on the production of coagulase and protein A.

[Effect of surface-active agents on staphylococcal coagulase]. / Vliianie poverkhnostno-aktivnykh veshchestv na koagulazu stafilokokka.

The influence of catamine AB, sulfonol NP-3, sodium alkylsulfate homologues (C10-C16) and of syntanol DT-7 on the reaction of fibrin formation under the action of the partially purified coagulase was studied. Catamine and sulfonol inhibited the velocity of the reaction in the the concentrations over 0.002 and 0.01%, respectively. A reduction of the rate of reaction with catamine occurred chiefly as a result of the enzyme inactivation, whereas sulfonal influenced the intermediate products of the reaction. Inhibition of the rate of the reaction with the sodium alkylsulfate homologues was enhanced with the increase of the alkyl radical length and was the greatest for the tetradecyl sulfate sodium. Syntanol failed to influence the enzyme activity, but increased its amount in the staphylococcus culture on the medium with subbacteriostatic concentrations of sulfactants. Catamine, sulfonol and, to a lesser extent, syntanol retarded the coagulation process of human citrate plasma with pathogenic staphylococcus.