Staphylococcus aureus α-Toxin: Nearly a Century of Intrigue

Staphylococcus aureus secretes a number of host-injurious toxins, among the most prominent of which is the small β-barrel pore-forming toxin α-hemolysin. Initially named based on its properties as a red blood cell lytic toxin, early studies suggested a far greater complexity of α-hemolysin action as nucleated cells also exhibited distinct responses to intoxication. The hemolysin, most aptly referred to as α-toxin based on its broad range of cellular specificity, has long been recognized as an important cause of injury in the context of both skin necrosis and lethal infection. The recent identification of ADAM10 as a cellular receptor for α-toxin has provided keen insight on the biology of toxin action during disease pathogenesis, demonstrating the molecular mechanisms by which the toxin causes tissue barrier disruption at host interfaces lined by epithelial or endothelial cells. This review highlights both the historical studies that laid the groundwork for nearly a century of research on α-toxin and key findings on the structural and functional biology of the toxin, in addition to discussing emerging observations that have significantly expanded our understanding of this toxin in S. aureus disease. The identification of ADAM10 as a proteinaceous receptor for the toxin not only provides a greater appreciation of truths uncovered by many historic studies, but now affords the opportunity to more extensively probe and understand the role of α-toxin in modulation of the complex interaction of S. aureus with its human host.     

Inhibition of β-glucuronidase by chlorinated hydroquinones and benzoquinones

An earlier study of the metabolism of pentachlorophenol has shown that a metabolite, tetrachloro-p-hydroquinone, possessed pronounced inhibitory action on the activity of -glucuronidase from bacterial origin. Several other chlorinated hydroquinones and benzoquinones have now been studied with regard to their ability to inhibit -glucuronidase of various origin in vitro and in vivo.All the studied chlorinated hydroquinones and benzoquinones were found to be potent inhibitors of -glucuronidase of bacterial origin. D-glucaric acid-1.4-lactone was included for comparison and was found to be less active than the other studied compounds. The inhibition was found to be competitive in nature.No inhibitory effect of the benzo- and hydroquinones studied in vitro or in vivo could be demonstrated on -glucuronidase from livers. The result calls for precaution when using bacterial -glucuronidase to split urinary conjugates of glucuronic acid.

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Zusammenfassung Eine frühere Studie des Metabolismus von Pentachlorphenol hat gezeigt, daß ein Metabolit, Tetrachlor-p-hydrochinon, eine ausgesprochene Hemmwirkung auf die Aktivität der Bakterien--Glucuronidase besitzt. Verschiedene andere chlorierte Hydrochinone und Benzochinone sind jetzt auf ihre Fähigkeit, -Glucuronidase anderen Ursprungs zu hemmen, in vitro und in vivo, untersucht worden.Alle die untersuchten chlorierten Hydrochinone und Benzochinone zeigten sich als starke Hemmer der Bakterien -Glucuronidase. D-Glucarsäure-1.4-Lakton wurde zum Vergleich einbezogen und wurde weniger aktiv als die anderen Verbindungen befunden. Die Hemmung war kompetitiver Art.Kein Hemmungseffekt von Hydro-oder Benzochinonen konnte in vitro oder in vivo auf Leber--Glucuronidase gezeigt werden. Das Resultat mahnt zur Vorsieht, wenn Bakterien -Glucuronidase zur Spaltung von Harnkonjugaten der Glucuronsäure angewandt wird.

     

Complicated course of facial cellulitis caused by Staphylococcus aureus in a 13-year-old boy with neutropenia — an adverse event analysis

Background

Facial cellulitis is a rare disease in children, associated with high risk of complications among immunocompromised patients.

Objective

A report on complicated facial cellulitis in a neutropenic teenager with risk factor analysis. Case report: A 13-year-old boy with neutropenia was taken to hospital. He initially complained of severe pain and redness of the nose — treated as an allergy. The skin condition deteriorated, a dermatologist diagnosed erysipelas and recommended amoxicillin. Deformation, oedema, erythema, blistering and oozing erosions of the nose, high C-reactive protein and neutropenia were found upon admission. An ultrasound scan revealed abscesses in the subcutaneous tissue. Intravenous penicillin and clindamycin were administered. Methicillin-sensitive Staphylococcus aureus was isolated from the skin lesions. The boy required multiple surgeries and granulocyte-colony stimulating factor therapy.

Conclusions

Facial cellulitis may be severe in immunodeficient patients. Delayed, inadequate empiric treatment and communication difficulties may increase the risk of complications.     

Inhibition of acetylcholine turnover in rat hippocampus by intraseptal injections of β-endorphin and morphine

Summary Intraseptal administration of morphine (70 nmol) or -endorphin (0.7 nmol) reduced the rate of acetylcholine (ACh) turnover (TR_ACh) in rat hippocampus but not in striatum or cortex. These intraseptal injections failed to modify the ACh content and did not elicit analgesia. Naltrexone (15 mol/kg, i.p.) completely antagonized the decrease of hippocampal TR_ACh elicited by the two opiate receptor agonists. Furthermore, intraseptal injections of naltrexone partially blocked the decrease in hippocampal TR_ACh induced by intraperitoneal administration of morphine (70 mol/kg, i.p.). These data suggest that opiate agonists decrease hippocampal TR_ACh by regulating septal cholinergic neurons, and that this effect is not associated with analgesia.     

Muropeptide signature of inhibitors of protein synthesis correlates with β-lactam synergism against methicillin-resistant Staphylococcus aureus

Quinupristin/dalfopristin (Q/D) and β-lactams interact positively against methicillin-resistant Staphylococcus aureus (MRSA). The effect extends to other inhibitors of protein synthesis, but not to inhibitors of polynucleotide synthesis or assembly, or to Q/D plus non-β-lactam cell wall inhibitors. Moreover, electron microscopy studies have correlated this effect with a thickened cell wall. In this study, we sought to determine whether inhibitors of protein synthesis might produce a specific peptidoglycan muropeptide signature that would correlate with their positive β-lactam interaction. The muropeptides of six S. aureus isolates (three methicillin-susceptible and three MRSA) were analysed using high-performance liquid chromatography and mass spectrometry. Exposure to 0.25× the minimum inhibitory concentration of inhibitors of protein synthesis consistently produced three main alterations irrespective of methicillin resistance: (i) an increase in peak 12 (a cyclic dimer of glycine-containing disaccharide–tetrapeptide); (ii) an increase in poorly resolved late-eluting materials; and (iii) a decrease in peak 1 (a disaccharide–pentapeptide). Eventually, the rate of autolysis was also decreased, supporting the structural alteration of the peptidoglycan. Other drug classes did not produce these anomalies. An increase in peak 12 was also observed in staphylococci treated with fosfomycin, which decreases expression of the native penicillin-binding protein (PBP) 2 and 4. Parallel blockage of normal PBPs with β-lactams abolished the anomalies, indicating that they resulted from altered function of native PBPs. This underlines the potential of inhibiting both protein synthesis and transpeptidation simultaneously and suggests that such a drug combination strategy might be efficaciously exploited.     

Inhibition by viozan of extravasation induced in rat trachea by capsaicin is mediated exclusively by β2-adrenoceptors

The mechanism by which 2(3H)-benzothiazolone, 4-hydroxy-7-[2-[[2-[[3-(2-phenylethoxy)propyl]-sulphonyl]ethyl]amino]ethyl]-monohydrochloride (AR-C68397AA; viozan), a dual dopamine D2/beta2-adrenoceptor agonist which has shown promise in the treatment of chronic obstructive pulmonary disease (COPD), inhibits the extravasation of plasma protein induced by capsaicin in the tracheas of Brown Norway rats has been re-evaluated. Viozan (10-30 microg/kg given intratracheally; i.t.) inhibited dose-dependently the extravasation of plasma protein tagged with Evans Blue into rat trachea induced by capsaicin (10 microg/kg i.t.). Similar effects were seen with the selective beta2-adrenoceptor agonist, salbutamol (3-10 microg/kg i.t.), but the selective dopamine D2 receptor agonist, quinagolide (10-30 microg/kg i.t.), was inactive. The effects of viozan and salbutamol were abolished by propranolol (3 mg/kg) given intraperitoneally (i.p.) but unaffected by sulpiride (3 mg/kg i.p.). Thus, in c,ontrast to claims in the literature, a functional response to dopamine D2 receptor activation in a preclinical model of oedema arising from sensory nerve fibre activation in the rat lung could not be demonstrated. Moreover, no qualitative difference could be demonstrated between the response to a dual D2/beta2-adrenoceptor agonist and a selective beta2-adrenoceptor agonist. The observations call into question whether a dual D2/beta2-adrenoceptor agonist such as viozan would bring added benefit over established selective beta2-adrenoceptor agonists in the therapy     

Staphylococcus aureus α-Toxin Triggers the Synthesis of B-Cell Lymphoma 3 by Human Platelets

The frequency and severity of bacteremic infections has increased over the last decade and bacterial endovascular infections (i.e., sepsis or endocarditis) are associated with high morbidity and mortality. Bacteria or secreted bacterial products modulate platelet function and, as a result, affect platelet accumulation at sites of vascular infection and inflammation. However, whether bacterial products regulate synthetic events in platelets is not known. In the present study, we determined if prolonged contact with staphylococcal α-toxin signals platelets to synthesize B-cell lymphoma (Bcl-3), a protein that regulates clot retraction in murine and human platelets. We show that α-toxin induced α(IIb)β(3)-dependent aggregation (EC(50) 2.98 μg/mL ± 0.64 μg/mL) and, over time, significantly altered platelet morphology and stimulated de novo accumulation of Bcl-3 protein in platelets. Adherence to collagen or fibrinogen also increased the expression of Bcl-3 protein by platelets. α-toxin altered Bcl-3 protein expression patterns in platelets adherent to collagen, but not fibrinogen. Pretreatment of platelets with inhibitors of protein synthesis or the mammalian Target of Rapamycin (mTOR) decreased Bcl-3 protein expression in α-toxin stimulated platelets. In conclusion, Staphylococcusaureus-derived α-toxin, a pore forming exotoxin, exerts immediate (i.e., aggregation) and prolonged (i.e., protein synthesis) responses in platelets, which may contribute to increased thrombotic events associated with gram-positive sepsis or endocarditis.     

Inhibition of atherosclerotic lesion development in the ApoE-/- mouse by a novel β-oxa polyunsaturated fatty acid

Recent findings that a novel polyunsaturated fatty acid, β-oxa 23:4n-6, inhibits adhesion molecule expression on vascular endothelial cells and leukocyte adhesion led us to examine its ability to inhibit the development of atherosclerosis in the apoE-deficient (apoE) mouse. The mice were kept on normal chow or a high-fat/high-cholesterol diet for various periods and treated with either vehicle or β-oxa 23:4n-6 by the intraperitoneal route. The hearts and aortae were isolated and lesion development at the aortic root was determined. Morphometric assessment revealed that lesion development was a function of compensatory aortic enlargement, suggesting that measurement of plaque size per se is the appropriate assessment of lesion size. Using this criterion, we found that atherosclerosis development was reduced in response to β-oxa 23:4n-6, plaque size by 74% and aortic cross-sectional area by 62%, under an optimized regime. The number of foam cells per unit tissue area in the lesions of β-oxa 23:4n-6-treated mice was significantly reduced by 37.5%. The blood levels of β-oxa23:4n-6 in these mice exceeded the concentrations previously found to inhibit adhesion molecule expression in cultured endothelial cells. These data show that β-oxa23:4n-6 protects against experimental atherosclerosis, most likely by reducing the number of infiltrating monocytes.     

Characterisation of the β-lactam resistance enzyme in Acanthamoeba castellanii

β-Lactams are well known as the best antibiotics for inhibiting the cross-linking between adjacent polysaccharide chains and peptides in the peptidoglycan layer of bacterial cell walls, causing bacterial cell lysis. There are no reports on the action of and resistance mechanisms to β-lactams in protozoa. Acanthamoeba castellanii is a free-living protozoan pathogen capable of causing blinding keratitis and fatal granulomatous encephalitis. When Acanthamoeba is exposed to harsh conditions, it differentiates into the cyst stage to avoid environmental stresses, such as drug treatment. In this study, it was shown that the mature encystation rate of A. castellanii is decreased by treatment with cefotaxime (CTX) and clavulanic acid (CLA); however, the drugs do not kill the amoeba. We hypothesise that β-lactam antibiotics may disturb synthesis of the double cell wall during the encystation process of Acanthamoeba. Interestingly, CTX is considered a powerful β-lactam, whereas CLA is considered a weak β-lactam but an efficient β-lactamase inhibitor. It was demonstrated that Acanthamoeba expresses β-lactamases to prevent inhibition of the encystation process by β-lactams. To reveal the functions of Acanthamoeba β-lactamases, a recombinant Acanthamoeba β-lactamase was produced in Escherichia coli that conferred resistance to β-lactams such as CTX, cefuroxime, penicillin and meropenem. Consequently, we suggest that Acanthamoeba produces enzymes similar to β-lactamases to avoid interference from the environment. Here we provide a new point of view on an important gene responsible for drug resistance and advocate for the development of more efficient treatment against Acanthamoeba infection.     

金黄色葡萄球菌对达托霉素临床耐药性的研究进展

达托霉素(daptomycin,DAP)是一种环脂肽类抗生素,DAP作用机制与其他许多抗生素不同。DAP通过扰乱细胞膜对氨基酸的转运,从而阻碍细菌细胞壁肽聚糖的磷壁(酸)脂质(LTA)的生物合成。DAP主要作用于病菌细胞膜,DAP具有在体外抗绝大多数革兰阳性菌的作用。最近国际病例报告显示,有较多患者在服用此药治疗过程中产生了DAP耐药性(DAP-R)。金黄色葡萄球菌对DAP可能存在多种耐药机制,对DAP耐药性的临床产生过程也较为复杂,预防对DAP的耐药发生和合理治疗耐DAP金黄色葡萄球菌感染就显得尤为重要。     

脂质体包裹的反义寡核苷酸逆转耐甲氧西林金黄色葡萄球菌耐药性的研究

目的：用人工合成磷脂二棕榈酰磷脂酰胆碱（dipalmitoyl phosphatidylcholine，DPPC），二肉豆蔻酰磷脂酰甘油（dimyristoyl phosphatidylglycerol，DMPG）制备反义寡核苷酸阴离子脂质体并研究脂质体包裹的抑制耐甲氧西林金黄色葡萄球菌（methicillin resistant staphylococcus aureus，MRSA）耐药基因表达信号传导通路中BlaRlmRNA表达的反义寡核苷酸（antisense phosphothioate oligodeoxynucleotides，AS-ODNs）对MRSA耐药性的影响。方法：设计合成AS-ODNs；薄膜分散冻干法制备其脂质体；透射电镜观察脂质体的形态；离心纯化脂质体并用紫外分光光度计测定包封率、渗漏率；振荡法检测体外释放度；平板克隆形成实验计数菌落数CFU；微量法测定细菌生长曲线。结果：反义寡核苷酸阴离子脂质体大小均匀，为圆球体，包封率为77．38％，冷冻条件下保存1月后渗漏率为0．18％，体外释放度实验表明24h后约60％的药物从脂质体中释放，反义寡核苷酸脂质体可显著抑制MRSA生长，脂质体包裹的不同剂量的AS-ODNs中MRSA的菌落形成单位（CFU）与空白对照组比较明显减少，具有剂量依赖性，且效果明显优于未被脂质体包裹的AS-ODNs。结论：采用薄膜分散冻干法制备反义寡核苷酸阴离子脂质体，包封率较高，质量稳定，反义寡核苷酸脂质体能逆转MRSA的耐药性，效果明显优于单用AS-ODNs，可作为反义寡核苷酸进入细菌的载体。     

耐甲氧西林金黄色葡萄球菌的研究进展

耐甲氧西林金黄色葡萄球菌(MRSA)已成为医院感染重要的致病菌,MR-SA引起的感染,因其耐药高、死亡率高及经济负担重,成为威胁全球公共卫生安全的严重问题.MRSA多重耐药现象日益严重.了解MRSA的现状,才能更好地及时治疗并且尽可能避免MRSA感染,因此本文对MRSA的流行现状、临床感染、治疗药物、预防传播及经济负担等最新研究现状进行概述.     

长春市金葡菌耐药状况及耐甲氧西林金葡菌基因分型

目的调查长春地区临床分离金葡菌的耐药状况及Panton—Valentine杀白细胞素（PVL）分布情况；确定耐甲氧西林金葡菌（MRSA）染色体及葡萄球菌me~盒式染色体（SCCmec）基因分型。方法琼脂稀释法测定苯唑西林等17种抗菌药物对2004年6月～2005年1月长春市3家教学医院临床标本分离的83株金葡菌的最低抑菌浓度（MIC）；聚合酶链式反应（PCR）进行金葡菌的PVL基因检测；脉冲场凝胶电泳（PFGE）对MRSA菌株作染色体同源性分析。多重PCR方法检测MRSA的SCCmec基因分型。结果83株金葡菌中MRSA12株（占14．5％）；金葡菌PVL的基因阳性7株（占8．4％）。MRSA对β-内酰胺类、红霉素、克林霉素、庆大霉素、四环素、氟喹诺酮类耐药率均超过90％，对氯霉素、利福平耐药率分别为8．3％、58．3％。未发现对糖肽类及复方磺胺甲嗯唑耐药的MRSA。甲氧西林敏感金葡菌（MSSA）对青霉素G、红霉素、克林霉素、四环素、庆大霉素耐药率分别为95．8％、67．6％、49．3％、45．1％、26．8％，对头孢菌素、氯霉素、利福平、氟喹诺酮类、复方磺胺甲曙唑耐药率均低于20％。MRSA的PFGE显示为A、B两种类型，以A型为主，占92％（11／12），三家医院均有分布。MRSA的SCCmec分型．Ⅲ型为主75％（9／12）。结论长春市MRSA发生率低于国内报道平均水平；MRSA为两种不同类型克隆株，在不同医院间存在克隆传播；未发现社区获得性MRSA菌株。     

耐甲氧西林金葡菌的研究进展

耐甲氧西林金葡菌已成为医院及社区感染的主要病原菌之一.经重组获得的mec复合体是其产生耐药性的结构基础,并通过产生PBP2a表达抗药性,而金葡菌耐药性表达及表达程度还受其内在的固有基因影响.本文就其流行病学、耐药机制及检测方法研究进展作一综述.     

脓液中金黄色葡萄球菌的耐药性监测

目的分析脓液中金黄色葡萄球菌（SA）的耐药性。方法对内蒙古自治区人民医院2009年1月至2013年3月临床分离的227株金黄色葡萄球菌进行分析,细菌鉴定和药敏试验采用法国梅里埃威泰科VITEK2Compact全自动细菌培养鉴定仪。结果脓液中SA的病区来源主要为外科系统,骨科和普外科占52．0％（118／227）,脓液中耐甲氧西林金黄色葡萄球菌（MRSA）的分离为34．4％（78／227）,低于本院文献报道各种标本MRSA的分离率66．0％（194／294）（P〈0．05）。脓液中SA对利奈唑胺、万古霉素、替考拉宁、奎奴普丁／达福普汀和呋喃妥因的耐药率均为0,MRSA对复方新诺明的耐药率低于对甲氧西林敏感的SA（MSSA）（P〈0．05）,对其他抗菌药物MRSA的耐药性高于MSSA（P〈0．05）。β-内酰胺酶阳性和阴性的SA对呋喃类药物和糖肽类药物的耐药率均为0,对青霉素G耐药率前者98．0％（198／202）高于后者68．0％（17／25）,差异有统计学意义（P〈0．05）,对其他抗菌药物的耐药率,前者略高于后者,但差异无统计学意义（P〉0．05）。结论脓液中MRSA的检出率和耐药性较高,临床应继续加强无菌区MRSA的感染控制。     

金黄色葡萄球菌分布及耐药性分析

目的调查金黄色葡萄球菌的临床分布及对常用抗菌药物的耐药性。方法收集首都医科大学附属北京潞河医院2014年1月至2016年12月从住院患者标本中分离出763株金黄色葡萄球菌,用全自动微生物分析仪进行鉴定及药敏实验,用WHONET 5.6软件对病原菌资料进行统计分析。结果金黄色葡萄球菌标本主要来自痰液(62.8%)、分泌物(24.8%)、血液(3.7%)和支气管灌洗液(3.7%)等临床标本,科室主要来自重症医学科(29.0%)、普外科(10.7%)、呼吸科(9.3%)、神经外科(8.5%)等科室。耐甲氧西林金黄色葡萄球菌(MRSA)共检出374株,2014年至2016年MRSA检出率分别为46.6%,58.1%和42.6%,MRSA对环丙沙星、左氧氟沙星、莫西沙星耐药率均大于80%,对四环素耐药率大于75%,对克林霉素、红霉素、利福平和庆大霉素耐药率分别在45%~55%,60%~70%,45%~85%和50%~70%,其中2015年检出2株对利奈唑胺耐药的金黄色葡萄球菌。结论临床分离的金黄色葡萄球菌耐药严重,应加强对其耐药性监测,同时根据药敏结果合理选用抗菌药物。     

MRSA表面标志物PBP2a的检出与苯唑西林MIC的相关性分析

目的研究MRSA表面标志物PBP2a与苯唑西林MIC的相关性。方法收集62株金黄色葡萄球菌临床分离株,通过乳胶凝集试验和全自动细菌分析仪分别检测青霉素结合蛋白2a(PBP2a)和苯唑西林MIC值。结果62株金葡中32株PBP2a检测阳性,30株PBP2a检测阴性。苯唑西林MIC≥4μg/ml31株,苯唑西林MIC≤2μg/ml31株。在苯唑西林MIC≥4μg/ml的31株MRSA中30株PBP2a检测均为阳性。结论金黄色葡萄球菌耐苯唑西林的耐药水平与PBA2a的检出有较好的相关性。     

Emerging drugs on methicillin-resistant Staphylococcus aureus

Introduction: Methicillin-resistant Staphylococcus aureus (MRSA) has proven to be a prominent pathogen in hospitals and in the community, which is capable of causing a variety of severe infections. Until now, there has been a limited antimicrobial armamentarium for use against MRSA, of which glycopeptides and linezolid are the main agents used.

Areas covered: This review assesses current treatment and the agents being developed for MRSA infections. A search was conducted in PubMed for English-language references published from 2000 to 2013, using combinations of the following terms: ‘MRSA', ‘MRSA therapy', ‘gram (+) infections therapy', ‘new antibiotics', ‘vancomycin', ‘staphylococcus resistance', ‘oritavancin', ‘ceftaroline', ‘linezolid' and ‘tigecycline'. The clinicalTrials website was also searched with keywords regarding the new antibiotic agents against MRSA infections.

Expert opinion: There are a number of new agents, the place of which in therapeutic regimens is yet to emerge. New glycopeptides, such as dalbavancin and oritavancin, with long half-lives, enabling once-weekly dosing, and oral agents, such as iclaprim, may provide a treatment approach for outpatient therapy. A decision must be made regarding the most suitable agent for an individual patient, the site of infection and the place of therapy.